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Investigation of ground fissures at Kausaltar, Kathmandu by in-situ testing and spatial geographical mapping

Investigation of ground fissures at Kausaltar, Kathmandu by in-situ testing and spatial... On April 25th, 2015, the Gorkha earthquake jolted the central region of Nepal, causing extensive damage to buildings and grounds in the urban areas of Nepal. One embankment section of Kathmandu-Bhaktapur Road, crosses a small valley in the center of the Kathmandu Basin. The earthquake has caused this embankment to deform with its support- ing soil. Investigating the mechanism of this ground deformation from the geotechnical and geological viewpoints was deemed necessary to examine possible countermeasures. For this purpose, we conduct several in-situ tests such as microtremor measurements, standard penetration tests, and Multichannel Analysis of Surface Waves. These investi- gations make two soft soil layers emerge as a causative factor. The estimated 3D soil profile shows that the deformed ground overlaps the area where the weak soil layers are below the groundwater level. The 3D soil profile also suggests that groundwater lowering using existing wells can reduce the water-saturated area by 81%. Carbon dating shows that the causative layer formed before the Paleo-Kathmandu Lake dried up. Keywords: 2015 Gorkha earthquake, Kathmandu, Ground fissures, Standard penetration test, Multichannel analysis of surface waves, Spatial ground model Introduction within the subduction interface between the Indian plate The 2015 Nepal earthquake (M = 7.8), also called the underneath the Eurasian plate. Gorkha earthquake, was the worst natural disaster to OCHA (2015) estimated the death toll and the prop- hit Nepal since the 1934 Nepal–Bihar earthquake. Its erty loss caused by the Gorkha earthquake at 8891 and epicenter was located at Barpak, Gorkha (28.231° N, $7.1 billion, respectively; the latter is almost equivalent 84.731° E), as shown in Fig.  1a. The earthquake rupture to the annual national budget in Nepal. The govern - extended about 100  km to the east of the epicenter at a ment of Nepal (2015) reported two-thirds of all inju- strike of 295° (USGS 2015). The most recent earthquake ries within the Basin. The number of partially damaged of the same magnitude was the Nepal-Bihar earthquake structures was more than 511,000 throughout Nepal, in 1934. Nasu (1935) reported that the intense ground of which roughly 75,000 are located in the Kathmandu shaking was the primary cause of complete and partial Basin. These reports suggest that rapid urbanization has collapses of many buildings in three major cities in Nepal, increased the threat of earthquakes in the Kathmandu namely Kathmandu, Bhatgaon, and Patan. These major Basin. earthquakes occurred immediately below the Himalayas Many researchers, such as Chiaro et al. (2015), Shakya and Kawan (2016), McGowan et  al. (2017), and Wang et  al. (2016), described the structural or ground damage *Correspondence: shiga815@iis.u-tokyo.ac.jp in the Kathmandu Basin as follows; Institute of Industrial Science, Be-206, The University of Tokyo, 4-6-1, Komaba, Meguro, Tokyo 1538505, Japan Full list of author information is available at the end of the article © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 2 of 15 Fig. 1 Survey locations and local topography with ground offsets that appeared in Kausaltar and measurement by several investigation teams (Konagai et al. 2015; JICA 2015; Angster et al. 2015) a Entire Map with digital terrain model from JAXA b Regional Map with digital terrain model from JAXA c Local Map with overlaid on an aerial image from Google Earth Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 3 of 15 – The degree of building damage becomes more signifi - 10% probability of exceedance PGA within 50 years esti- cant toward the basin center. For example, the his- mated by JICA (2002) or Ram and Wang (2011). They torical architecture around Durbar Square (Fig.  1b) also pointed out that the local earthquake amplification suffered from complete collapse. In contrast, the characteristics of the Basin may have caused damage to damage to residential buildings was relatively low buildings. despite the fragility of common masonry structures. The thick lacustrine soil deposit is perhaps responsi - – Liquefaction traces were found at various locations, ble for long-period seismic motions. A deep borehole such as Jharuwarashi, Bungamati, and Nepal Engi- log obtained by Sakai et al. (2000) shows that a weak clay neering College, but damage to structures due to liq- layer called Kalimati formation lies between 15 and 40 m uefaction was limited. in depth. A series of magnetostratigraphic and paleonto- logical observations by Katel et  al. (1996) revealed that lacustrine formations stacking one on the other could be Several research reports pointed out that basin-spe- 600  m thick in the Basin. Sakai et  al. (2016) conducted cific seismic motion has caused damage to structures. a thorough sedimentary survey and carbon dating to For example, Takai et  al. (2016) obtained strong ground investigate several water-lowering events that geologists motions at one rocky site and three sedimentary soil believe occurred in the Paleo-Kathmandu Lake. They sites in the Kathmandu Basin and compared them with reported that although the cause of the lowering is still the seismic record at the USGS KATNP Station (USGS, unclear, there were at least two significant decreases in 2015), as shown in Fig.  1b. They found that horizontal the lake water level. They also concluded that the Paleo- components of long-period oscillation had substantial Kathmandu Lake dried up about 12,000 years ago. power to damage high-rise buildings at the sedimentary Although the ground in the other area of the Kath- soil site, as shown in Fig.  2. Some other papers, such as mandu Basin rarely deformed, a severe ground displace- Parajuli and Kiyono (2015), Bijukchhen et al. (2017), and ment occurred at Kausaltar, about 2  km southeast of Wang et  al. (2016), reported that long-period seismic Tribhuvan International Airport. Some cracks and fis - motions of 1 to 2 s were observed in the mainshock and sures as long as 400  m maximum appeared on a gently aftershocks, and these tremors mainly caused damage sloping alluvial hill. This paper discusses when the causa - to low-rise structures in the Kathmandu Basin. Sharma tive layers have formed, how the ground has deformed, et  al. (2017) showed that the PGA did not exceed the Fig. 2 Observed ground accelerations at one rock site (KTP), three sedimentary sites ( TVU, PTN, and THM) by Takai et al. (2016), and one sedimentary site (KATNP) by USGS (2015) (Reprinted from Takai et al. (2016)) Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 4 of 15 and future potential ground hazards through several in- situ testings, carbon dating, and GIS mapping. Study area Kausaltar (27.6745° N, 85.3607° E), about 2  km southeast of the Tribhuvan International Airport of Kathmandu, is a residential area spreading over ter- races constituting the upper part of the sedimentary sequence of the Kathmandu Basin (Fig.  1c). An about 500 m embankment section of the Kathmandu-Bhakta- pur Road, a part of Araniko Highway, crosses a small shallow swampy valley in the Basin diagonally. 200– 400  m long fissures associated with vertical ground offsets appeared diagonally across this road (Konagai et al. 2015). These fissures ran almost parallel, trending in NEE to SWW direction and slightly bent to the east after crossing the road. These fissures associated with Fig. 3 A sand-filled fissure that appeared on a wall of Trench-1 excavated by Angster et al. (2015) vertical offsets indicate that the soil mass on the north - western slope slumped as a whole and moved slightly towards the shallow and swampy valley, which runs Subedi and Acharya (2022) calculated the factor of almost parallel to these fissures. The most extended safety against liquefaction in the Kathmandu Basin and crack bordering the southeastern end of the deformed reported that the factor of safety around Kausalter was area was accompanied by the most prominent vertical less than 0.5 during the 2015 mainshock. offset reaching 2  m. Other shorter fissures appeared on the other side of the valley. Both sides of the val- Objective and methodology ley seem to have moved against each other, causing the Previous studies have presented important clues for middle part of the Highway section to be slightly bent discussing the causes of this ground deformation; the upwards. At the same time, only minor damage was clues include sand-filled fissures, the presence of shal - observed in the reinforced retaining walls and the earth low organic soil layer or clayey soil, etc. However, they embankment of Kathmandu-Bhaktapur Road (Sharma just provided us with information point-wise and did and Deng 2016). not consider the historical sedimentary environment in There are various theories for the cause of this ground Kausaltar. To cover a much wider extent of the deformed deformation in Kausaltar discussed by many research- ground and clarify how the causative layer formed, we ers. Sharma et  al. (2019) and Okamura et  al. (2015) conducted the following in-situ tests; reported a 2-m deep fissure associated with an about 1.5-m vertical scarp. Sharma et  al. (2019) have raised 1. Microtremor measurements, two causative soils: a lacustrine clay called Kalimati 2. Multi-channel analysis of surface wave (MASW), Clay and liquefiable sand. Angster et  al. (2015) exca - 3. Standard penetration test (SPT), vated a 2.5  m deep trench across the scarp and found 4. Real-Time kinematic global navigation satellite sys- a sand-filled fissure on the trench wall (Fig.  3). Moss tem survey (RTK-GNSS survey), and. et  al. (2015) first thought the causative soil was Kali - 5. Carbon dating. mati Clay. But seeing thin planner intrusions of sand exposed on the trench wall, they finally deduced the Integrating the obtained data sets on GIS, we created causative soil was the liquefiable sand. Maharjan (2017) a 3D hydrogeological model for the shallow part of the attributed the lateral spreading to cyclic shear soften- lacustrine soil deposit of Kausaltar. The groundwater ing of a silty clay lacustrine deposits. He also reported level and two soil layers were estimated through Inverse that a resident witnessed that the fissures had devel - Distance Weighting (IDW, hereafter). In addition, we oped longer and deeper during the Mw6.7 aftershock assumed an axisymmetric pumping model in a homoge- on May 12th, 2015. Tiwari et  al. (2018) conducted in- neous soil to discuss the effect of lowering the groundwa - situ sounding tests and numerical analyses. They found ter level through temporary wells. This section describes that the lacustrine clayey deposits had deficient shear these methods in detail. strength and were highly vulnerable to slope instability. Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 5 of 15 Microtremor measurement C (ω) = U (ω)U (ω) ij i j We conducted microtremor measurements in Kausal- tar and the downtown area of Kathmandu near the USGS where, U (ω) and U (ω) are Fourier Spectra of u (t) and i j i KATNP station at 27.7124° N, 85.3156° E. A seismometer u (t) , resp e ctively . (CV-374AV, Tokyo Sokushin Co. Ltd.) measures the three The phase components of this cross-spectrum C (ω) ij orthogonal components of the ambient ground motion. The are precisely the phase differences at all frequencies range of frequencies that this seismometer can record is between the two points i and j. u Th s, given C (ω) , we ij from 0.1 to 100 Hz. We measured ambient ground motions obtain the dispersive nature of the Rayleigh wave, and we at 7 points on the deformed ground on the northwestern can back-analyze the stiffness profile of the layered soil side of the Highway (BH-1 and BH-3 ~ 8 in Fig. 1c), 3 points medium (Haskell 1953 or Saito 2006). on the adjacent intact ground (BH-9, MT-1, and MT-2 in Fig. 1c), and 4 points next to the KATNP observatory. Standard penetration test We calculated the spectral ratios between the ambi- We conducted Standard Penetration Tests (SPT) at five ent ground motion’s horizontal and vertical components boreholes, BH-5, BH-6, BH-7, BH-8, and BH-9, follow- (H/V ratios) at these points by applying the 0.05  Hz ing JIS A1219 (Japan Standards Association 2013), in Parzen window in the frequency domain. The ratios are December 2016 and April 2017. Besides them, the Japan independent of the source distance and significantly con - International Agency (JICA 2015) drilled four more tribute to the site-specific effect evaluation. boreholes as a part of its rapid recovery project in August Nakamura (1989), Tokimatsu and Miyadera (1992), and 2015. At each borehole, a thick-walled sample tube was Lermo and Francisco (1994) considered that the H/V driven down by blows from a slide hammer with a mass ratio could be related to the ellipticity ratio of Rayleigh of 63.5 kg falling through a height of 760 mm. The sam - waves representing the intrinsic nature of the underly- pler is first driven to a depth of 15 cm below the bottom ing layered soil medium. When impedance contrasts of the pre-bored hole. Then, we count the blows (SPT-N between the soft surface soil and the underlying stiff bed value) required for the second, third and fourth 10 cm of stratum, a clear peak in the H/V spectral ratio can appear penetration. Previous studies have shown that the SPT-N at the natural frequency of the layered soil medium value can correlate with physical parameters such as (Tokimatsu and Miyadera 1992). The observation can shear wave velocity (Kokusho and Yoshida 1997), density explain this trend in that the horizontal component (H ) (Cubrinovski and Ishihara 1999), and internal friction reflects the response characteristics of the layered soil angle (Hatanaka and Uchida 1996). medium. In contrast, the vertical component (V ) retains the vibration characteristics of the bed stratum. Carbon dating Carbon dating is a method that provides objective age Multi‑channel analysis of surface waves estimates for carbon-based materials that originated Multi-channel Analysis of Surface Waves (MASW) was from living organisms. We have taken organic soil sam- performed along two lines (Lines 1 and 2 in Fig.  1c) on ples from various depths of the three boreholes (BH-7, the deformed ground to evaluate the shear wave velocity BH-8, and BH-9 in Fig. 1c) and the surface of a cut slope (v ) profile of the shallow layered soil. Lines 1 and 2 are (Fig.  1c), which was by chance excavated to construct a 72  m and 208  m long, respectively. The equipment used retaining wall near the shallow swampy valley. in this study, McSEIS-SW, OYO Corporation, allows us to There are three radioisotopes in carbon atoms; C, obtain an underground 2D Surface wave velocity struc- 13 14 C, and C. Scientists estimate that the ratio of these ture. The 24-bit resolution equipment records the ground radioisotopes in the atmosphere is almost constant, tremor at the minimum time interval of 0.0625 ms. –10 98.9:1.1:1.2 × 1.0 , because of the nitrogen formation The phase velocity of the Rayleigh wave that trav - by cosmic ray collisions and the beta decay of C itself. els horizontally through a layered soil medium dif- However, when samples move to an environment unaf- fers from frequency to frequency. Namely, the Rayleigh fected by cosmic rays, the percentage of C decreases. wave’s phase velocity dispersive nature reflects the lay - u Th s, knowing the C half-life of 5730 ± 40 years, we can ered structure of the soil medium. Following the algo- estimate when the organism died. rithm developed by Park et  al. (1999), we first compare We collaborated with the dating laboratory at the each pair of the ground tremor signals in the frequency University of Tokyo Museum. The samples were first domain through the cross-spectral density (CSD) analy- immersed in hydrochloric acid to remove contaminants sis. The cross-spectrum C (ω) of any arbitrary pair of ij and fulvic acid. Secondly, their carbon contents were ground tremor signals u (t) and u (t) is given by: i j Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 6 of 15 measured. When the measured carbon content exceeded common to carry out 3D seepage flow analysis. How - 10%, the carbon dioxide was vacuum-sealed with copper ever, due to remaining uncertainties in the underground oxide and sulfide in a double-sealed quartz glass tube and hydrological parameters, this study performed a pseudo- heated in an electric furnace to 850  °C for 3  h. Thirdly, 3D analysis using a much simpler model by Dupuit the carbon dioxide was purified using a vacuum line. The (1863). The basic formulation is as follows; collected carbon dioxide was then sealed inside a furnace R 2πh k tube with an iron catalyst and hydrogen and was reduced log = (H − h) r Q to carbon by heating the furnace tube at 650  °C for 6  h. Finally, we used an accelerator-mass-spectrometer to where R is the radius of the influence circle, r is the detect the amount of radioactive carbon. radius of a well, h is the thickness of a causative perme- able layer, k is the permeability coefficient, Q is the dis- RTK GNSS measurement charge from the well, H is the height of the static water To treat the in-situ geotechnical test results at each loca- table from the well bottom, and h is the height of water in tion as spatial information in GIS, highly accurate location the well from the well bottom. The radius of the influence information is required. Therefore, we measured latitude circle was calculated by using the empirical equation by and longitude by RTK (Real-Time Kinematic) positioning Kyrieleis and Sichardt (1930); using GNSS (Global Navigation Satellite System). GNSS is a method to determine the positional coordinates of a receiv- R = 3000s k ing station by launching several satellites into orbit. Each sat- where s is the amount of lowering and equal to H − h . ellite transmits radio waves containing the timing and orbital Based on Creager et  al. (1945), the permeability coeffi - information of the satellite. The receivers then use this data cient k is empirically given by; to determine location. RTK positioning is one of the GNSS- based interferometric positioning methods. It determines 2.2954 k = 0.0034(D ) the position coordinates by simultaneously receiving radio waves from satellites at base and rover stations to remove with D (mm) as the particle size for which 20% of the common errors such as multipath and satellite clock devia- material is finer. tion. RTK-GNSS enables us to determine locations vertically and horizontally with an accuracy of a few centimeters. Results and discussion Vibration characteristics Inverse distance weighting (IDW) Figure  4 shows the H/V spectral ratio obtained at each We use IDW as a spatial interpolation method given scat- location. This figure indicates that all H/V spectral ratios tered locations on the ground with known measured val- show relatively large values in a frequency range lower ues to estimate values at other unknown points. IDW than 1 Hz. As seen in Molnar et al. (2017); Pandey (2000), is easier to use than the Kriging method because IDW the relatively low dominant frequency may reflect the pres - employs a simple formula to calculate unknown values ence of a thick lacustrine deposit in the Paleo-Kathmandu at the prediction location. On the other hand, unlike the Lake. However, nothing shown in Fig.  4 seems to assure Kriging method, IDW does not assume a probability distri- the difference between the deformed and intact grounds. bution, and therefore, the estimation error is not available. Table 1 shows the dominant frequency of microtremor The value y(x) at a prediction location, x is calculated by at each location. As discussed in von Seht and Wohlen- available values y(x ) at known points x ( i = 0, 1, . . . , N ) i i berg (1999) and Delgado et  al. (2000), the spectral ratio as follows; has also been used to characterize qualitatively the sub- surface structure, especially the thickness of soft sedi- w (x)y(x ) i i i=0 ments. In a simplified two-layer ground structure, the y(x) = w (x) j wavelength of the shear wave at the lowest vibration j=0 mode, assuming the lower base layer as its fixed end, where, equals 1/4 of the layer thickness of the soft ground layer, L . Therefore, the dominant frequency f can be given by; s d w (x) = |x − x | s f = 4L One‑dimensional pumping model where v is the shear wave velocity of the upper soft When discussing the amount of pumping water or effec - ground layer. Table  1 shows that BH-1, BH-3, and BH-8 tive stress due to lowering the groundwater level, it is have relatively low dominant frequencies among the Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 7 of 15 Fig. 4 Microtremor H/V spectra at the observation sites in the undeformed area, the less-deformed area in Kausaltar, and near the KATNP observatory frequency shows that the softer surface layers are Table 1 Dominant frequency at the observation sites thicker or have smaller v as we come closer to the High- Deformed area Less deformed area Referenced area way. However, since the dominant frequencies near the Name Dominant Name Dominant Name Dominant KATNP observatory are roughly the same, we cannot frequency frequency frequency argue the damage extent based only on those frequencies. BH-1 0.16 BH-9 0.34 USGS-1 0.18 Figure  5 compares the variation of amplitude ratio in BH-3 0.59 MT-1 0.29 USGS-2 0.15 the frequency domain with the average Fourier spectrum BH-4 0.15 MT-2 0.52 USGS-3 0.21 of microtremors near the KATNP observatory as the reference. The red and black lines are for the deformed BH-5 0.56 USGS-4 0.26 and intact grounds in Kausaltar, respectively. The spike BH-6 0.33 that appears at 40  Hz is probably due to an unexpected BH-7 0.54 external or internal noise of the seismograph. It is per- BH-8 0.20 haps premature to deduce the essential nature of the ground at Kausaltar only from Fig.  5 without knowing measured locations in the deformed area. These points the real picture of the source of ambient microtremors are close to the eastern or western slopes of the High- in the Basin. However, compared with the area near the way, where the worst damage was. The low dominant Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 8 of 15 5.0 BH-3 Horizontal Components BH-3 Vertical Components 4.0 MT-2 Horizontal Components MT-2 Vertical Components 3.0 2.0 1.0 0.0 0.11 10 Freqency(Hz) Fig. 5 Variation of frequency-domain amplitude ratio at BH-3 and MT-2 with the Fourier spectrum of the microtremor observed at USGS-3 as the reference Fig. 6 Spatial distribution of v obtained through Multichannel Analysis of Surface Waves Subsurface soil profile KATNP observatory, the ground at Kausaltar is more Spatial distribution of shear wave velocity easily shaken over the frequency range larger than 5 Hz. Line 1 and Line 2 in Fig.  1c cross several ground fis - This tendency is more apparent in the seriously deformed sures diagonally. Figure  6 shows the estimated spatial area. Ratio between the Fourier spectra of ambient ground motions at Kausaltar and USGS KATNP observatory Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 9 of 15 distribution of shear wave velocity. The blue color shows peat and organic soils tend to have lower internal friction higher shear wave velocity values, while the red color angles at the same density. Tsushima and Oikawa (1982) shows lower shear wave velocity values. reported that undrained shear strength decreases with Rix  and Leipski (1991) concluded that the best over- increasing moisture content. Thus, the relative height of all accuracy and resolution in spectral analysis of sur- the organic soil layer to the groundwater level can indi- face waves was obtained when the maximum wavelength cate whether it softened or not. is one to two times the maximum desired depth of the A silty sand layer with almost the same v value as the shear wave velocity profile. Based on the above conclu - deeper low v layer was identified at 4–8  m beneath the sion, Park et  al. (1999) recommended using the half- ground surface. Some part of this layer was below the wavelength (maximum offset of seismic sensors) as a aquifer level. Several samples containing very thin tabu- reasonable depth. Therefore, the measurable depth in this lar sand-filled fissures were found, suggesting the pres - survey is about 12  m. The inverse analysis of the shear ence of a liquefiable layer beneath them. Many laboratory wave velocity profile is usually performed using the ini - tests show that liquefaction resistance is reduced when tial estimation for the ground depth of about one-third the soil’s non-plastic content is high (Polito and II 2001; of the wavelength. We made the initial estimation from Carraro et al. 2003). Therefore, the relative position of the the SPT-N values at the nearby boreholes. The initial soft layer to the groundwater level is vital in determining estimates of the shear-wave-velocity profile from differ - the causative layer. ent sets of SPT-N values can cause the final assessment of the velocity profile to differ, particularly for the deeper GIS analysis ground. We have deduced the upper surfaces of the above-men- Looking at the shallow part of the ground in Fig.  6, a tioned organic layer, the silty sand layer, and the ground- low v zone (1) spreads 3 to 5  m underground over the water level using the IDW method. The organic soil entire stretch of both Line 1 and 2. The value of v is layer lies mainly on the valley’s eastern slope, crossed around 140 m/s at 2 to 4 m below the ground surface in by the Highway (BH-7, 8, and 9). Part of the organic soil Line 1. The borehole (BH-5), projected on Line 1 as the also appears on the surface of the western valley slope, arrow in Fig.  6, is located almost on the extension of the where we took samples for carbon-dating. However, the fractures. The estimated soil profile along Line 1 shows deduced 0.5 m to 1 m thick organic soil layer is not seem- that v is greater than 180 m/s over 5 to 8 m depths along ingly causative because the organic layer lies above the the borehole. In contrast, a shallower and softer soil layer deduced groundwater surface (Fig. 8b). Moreover, exten- with v =160  m/s spread towards the valley side from sive fissures appeared even in the area where we found the borehole. A low shear wave velocity layer of 110 to no organic soil layer in BH-5 and BH-6. It is thus unlikely 130  m/s lies at 2 to 4  m below the ground surface along that this soil layer is responsible for the extensive lateral Line 2 in Fig.  6. One more slightly lower shear wave spreading. velocity layer of 140  m/s at 5 to 8  m below the ground The height difference between the upper surface of the surface straddles the two significant fractures. These aquifer and the lower surface of the silty sand layer was two soft layers can be considered possible causes of the obtained at each borehole in the target area, and spatial fissures. variation of the height difference was deduced as shown in Fig.  8b. It stands out that the orange area where the SPT silty sand beneath the aquifer overlaps the area of fis - Figure  7 shows the soil classifications and SPT N-value sures associated with vertical ground offsets (white lines). distributions for all boreholes. SPT N-value can be cor- Though the aquifer level may fluctuate occasionally, this related with the hardness of the soil. N-values are at most fact strongly suggests that the deeper silty sand layer ten over the almost entire stretches of BH-7, BH-8, and beneath the aquifer could have been the primary cause of BH-9. These boreholes are closer to the swampy val - the lateral spreading. ley than the others. Groundwater levels in BH-5, BH-6, BH-7, and BH-8, shown by broken blue lines in Fig.  7, Possible countermeasure lie between 4.4 and 7.3  m underground. We found no To prevent the water-saturated silty sand layer from groundwater table in BH-9. softening in a future earthquake, we propose ground- We also found organic soils above the groundwater water lowering using locally available wells as a practi- level from the extracted core samples. The depths of cal measure. The Google Earth satellite image obtained these organic soils were consistent with the depths of on November 11th, 2015, shows 70 houses in the the upper low v layers. Several research reports, such deformed area; all these houses presumably have wells. as Huat (2006) and Blanco-Canqui et  al. (2005), showed We also assume that 14 extra wells will be excavated in Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 10 of 15 Fig. 7 Soil classifications and SPT N-value distributions at 5 boreholes. Blue dotted lines show the initial water level of each borehole after reaching that depth open spaces. Figure  9 again shows the height difference consolidation. For example, Yasuda and Hashimoto between the upper surface of the aquifer and the lower (2016) reported that the maximum subsidence of 7.8 cm surface of the silty sand layer. In this figure, however, was reached in Japan due to groundwater pumping as a the upper surface of the aquifer is assumed to be 1.75 m measure against liquefaction. The sandy soil layer sus - higher than what we observed to be on the safe side of pected to have liquefied in the earthquake contains fine the discussion, considering the seasonal fluctuation of substances, which may cause slow dissipation of excess the aquifer level. pore water pressure and thus require more time to set- As shown in Fig.  10, when 4.2  m /day of water is tle. Further studies will be required to implement this withdrawn at each well, the area overlying the water- measure. 4 2 saturated silty sand layer decreases from 2.9 × 10  m to 3 2 5.6 × 10  m . Carbon dating Lowering the groundwater level is an effective way to Carbon dating revealed that organic soil lies around increase effective stress in soils and reduce the likeli - 1.9  m, 5.5  m to 6.0  m, and 3.0  m beneath the ground hood of liquefaction occurrence. However, it has some surface at BH-7, BH-8, and BH-9. Table  2 shows the disadvantages, such as ground subsidence due to soil depths of the organic soils, the calibrated soil ages, and Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 11 of 15 Fig. 8 Difference between the upper surface of the aquifer and the upper surface of two suspicious layers in Kausaltar. a Organic layer b Silty sand layer Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 12 of 15 Fig. 9 Difference between the upper surface of the aquifer and the lower surface of the silty sand layer in Kausaltar (before lowering groundwater level) the estimation errors. Figure 11 also shows the calibrated caused an embankment section of the Kathmandu- ages of the organic soil samples and their elevations. Bhaktapur Road (Highway) to deform with its support- The estimated age varies from BC 9,300 to BC 13,100. ing soil. Extensive 200–400  m long fissures traversed These periods overlap when the Paleo Kathmandu Lake the embankment diagonally, and the ground spread has been drying around BC 10,500 (Sakai et  al. 2016). laterally toward a shallow swampy valley. We have Several samples were taken at different depths along conducted field surveys and studied the potentially BH-8 and BH-9. The shallower the samples are, the older causative factors. Here are the conclusions: are the estimated ages. Perhaps, it is because shallower carbon-fixing flora exposed to air earlier than deeper 1. H/V ratios obtained at several points near the dam- flora as the Paleo-Kathmandu Lake dried up. The result aged Highway embankment exhibited peaks at low suggests that the strata below the organic soil layers, such frequencies. They suggested that the soft surface as the causative silty soil, were significantly influenced by layer can be thicker as we come closer to the High- the initial depositional environment of the Paleo Kath- way. mandu Lake. Strata with similar mechanical properties 2. Multi-channel Analysis of Surface Waves showed may spread wide in the Kathmandu Basin. the presence of two soft soil layers. One spreads 2 to 4  m underground over the entire stretch of the tar- get area, while the other spreads 5  m underground, Conclusion mainly on the lower side of the swath of ground fis - The 2015 Gorkha earthquake caused extensive damage sures. Standard Penetration Tests (SPT) also revealed in the rugged mountain areas and the flat Kathmandu the presence of two weak layers; a shallower weak Basin. The collapse of masonry structures and local - organic soil layer 2 to 5 m deep and a deeper soft silty ized soil liquefaction featured the damage reported sand layer 5 to 8 m deep beneath the ground surface. in the Basin. Among them, the ground deforma- tion near Kausaltar was unique. The earthquake has Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 13 of 15 Fig. 10 Difference between the upper surface of the aquifer and the lower surface of the silty sand layer in Kausaltar (After lowering groundwater level) Table 2 Obtained ages of organic soils found at BH-7, BH-8, BH-9, and the cut slope Name Depth (m) Calibrated age ± Error (BC) Cut slope 9751 294 BH-7 − 1.83 ~ − 1.90 9538 217 BH-8 − 5.32 ~ − 5.44 10,583 108 − 5.43 ~ − 5.50 10,215 211 − 5.65 ~ − 5.78 10,042 157 − 5.81 ~ − 5.97 11,181 65 BH-9 − 2.84 ~ − 3.00 12,815 309 − 3.20 ~ − 3.40 10,364 203 Fig. 11 Relation diagram between calibrated age and elevation of organic soil sample 3. The deeper silty sand layer beneath the aquifer over - laps the area of lateral spreading associated with extensive fissures. Though the aquifer level may fluc - could have formed when the Paleo-Kathmandu Lake tuate occasionally, this fact strongly suggests that the was drying up. Thus, weak soil layers like those found deeper silty sand layer beneath the aquifer could have at Kausaltar can spread wide in the Kathmandu been the primary cause of the lateral spreading. Basin. 4. Carbon dating for organic soil samples taken from boreholes indicated that these organic soil layers Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 14 of 15 Declarations The third finding suggests that groundwater lowering using locally available wells will increase effective stress Competing interests in soils and thus reduce the likelihood of liquefaction The authors declare that they have no competing interests. occurrence in future earthquakes. This measure may Author details cause some side effects, such as ground subsidence due Institute of Industrial Science, Be-206, The University of Tokyo, 4-6-1, Komaba, to soil consolidation. Further studies will be required to Meguro, Tokyo 1538505, Japan. International Consortium on Landslides, 138-1, Tanaka-Asukai, Kyoto, Sakyo 6068226, Japan. Ear th I nvestigation figure out if this measure is feasible. and Solution, Nepal Pvt. Ltd, Kirtipur-2, Kathmandu, Nepal. Depar tment of Civil and Environmental Engineering, 805, Building No.1 of Mechanical Con- struction, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, List of symbols Niigata 9402188, Japan. SPT: Standard penetration test; MASW: Multi-channel analysis of surface wave; KATNP: Kathmandu, Nepal observatory of the United States geological survey; Received: 1 October 2021 Accepted: 3 May 2022 JICA: Japan international cooperation agency; USGS: United States geologi- cal survey; OCHA: United Nations office for the coordination of humanitarian affairs; PGA: Peak ground acceleration; GIS: Geographic information system; RTK-GNSS: Real-time kinematic global navigation satellite system; IDW: Inverse distance weighting; BH: Borehole; JIS: Japanese institute of standards; u (t): References Horizontal displacement; u (t): Vertical displacement; t : Time; u (t): Displace- v x Angster S, Fielding EJ, Wesnousky S, Pierce I, Chamlagain D, Gautam D, Upreti ment in x-axis direction; u (t): Displacement in y-axis direction; : Frequency; y f BN, Kumahara Y, Nakata T (2015) Field reconnaissance after the April 25th : Horizontal fourier spectrum; : Vertical fourier spectrum; : Dis- H(f ) V (f ) u (f ) 2015 M 78 Gorkha earthquake. Seismol Res Lett 85:1506–1513 placement at point i; : Fourier spectrum at point i; : Cross-spectrum C (f ) U (f ) ij Association JS (2013) JIS A1219:2013 Method for standard penetration test. of point i and point j; x: Position vector; y(x): Scalar physical quantity at Bijukchhen S, Takai N, Shigefuji M, Ichiyanagi M, Sasatani T (2017) Strong position x; w(x): Weight by distance; R: Radius of influence circle; r : Radius of motion characteristics and visual damage assessment around seismic well; h : Thickness of a causative permeable layer; k: Permeability coefficient; : 0 Q stations in Kathmandu after the 2015 Gorkha, Nepal earthquake. Earthq Discharge from well; H: Height of static water table from well bottom; h: Height Spectr 33(1_suppl):219–242. https:// doi. org/ 10. 1193/ 04291 6eqs0 74m of water in the well from well bottom; s: Amount of lowering; D : Particle size Blanco-Canqui H, Lal R, Owens LB, Post WM, Izaurralde RC (2005) Strength for which 20% of the material is finer.; : Dominant frequency; v : Shear wave f s properties and organic carbon of soils in the North Appalachian region. velocity; L : Layer thickness of the upper soft ground layer. Soil Sci Soc Am J 69(3):663–673. https:// doi. org/ 10. 2136/ sssaj 2004. 0254 Carraro JAH, Bandini P, Salgado R (2003) Liquefaction resistance of clean and Acknowledgements non-plastic silty sands based on cone penetration resistance. J Geotech The author’s special thanks go to Mr. Masashi Ogawa, Mr. Shinya Machida, and Geoenviron Eng 129(11):965–976. https:// doi. org/ 10. 1061/ (ASCE) 1090- Mr. Makoto Oyama, at the Embassy of Japan, Kathmandu, Nepal. We would 0241(2003) 129: 11(965) also like to thank Professor Tara Nidhi Bhattarai, and Prof. Danda Pani Adhikari, Chiaro G, Kiyota T, Pokhrel RM, Goda K, Katagiri T, Sharma K (2015) Reconnais- Department of Geology, Tribhuvan University, for sharing valuable information sance report on geotechnical and structural damage caused by the 2015 on the local situation. Our thanks also go to Dr. Akira Nakamura, Mr. Kazuki Gorkha earthquake, Nepal. Soils Found 55(5):1030–1043. https:// doi. org/ Shimada, and Mr. Sanumasa Kazui, Infrastructure and Peacebuilding Depart- 10. 1016/j. sandf. 2015. 09. 006 ment, Japan International Cooperation Agency, who have kindly provided Creager WP, Justin JD, Hinds J (1945) Earth, rock-fill, steel and timber dams. Eng the authors with essential pieces of information regarding damage caused by Dams III:648–649 the 2015 Gorkha Earthquake as well as every convenience for field surveys. Cubrinovski M, Ishihara K (1999) Empirical correlation between SPT N-value Furthermore, we wish to acknowledge Dr. Minoru Yoneda, Dr. Takayuki Omori, and relative density for sandy soils. Soils Found 39(5):61–71. https:// doi. and Mr. Hiromasa Ozaki, Laboratory of Radiocarbon Dating, The University org/ 10. 3208/ sandf. 39.5_ 61 of Tokyo, for providing us with ages of soil samples containing soil samples Delgado J, Casado CL, Giner J, Estevez A, Cuenca A, Molina S (2000) Micro- organic matters through carbon dating. The authors also would like to express tremors as a geophysical exploration tool: applications and limitations. their sincere gratitude to Mr. Shogo Aoyama for conducting the borehole Pure Appl Geophys 157(9):1445–1462. https:// doi. org/ 10. 1007/ PL000 drilling and physical tests. Finally, the authors wish to thank the tremendous help given by Dr. Alessandra Mayumi Nakata Kaiami, Mr. Hikaru Tomita, and Dunod Gautam D, de Magistris FS, Fabbrocino G (2017) Soil liquefaction in Mr. Bhandari Basant in the field investigations. Kathmandu valley due to April 25th 2015 Gorkha, Nepal earthquake. Soil Dyn Earthq Eng 97:37–47. https:// doi. org/ 10. 1016/j. soild yn. 2017. 03. 001 Author contributions Dupuit J (1863) Études théoriques et pratiques sur le mouvement des eaux MS analyzed and interpreted all of the site-investigation data regarding the dans les canaux découverts et à travers les terrains perméabls: avec des borehole log and microtremors. KK showed the overall direction of the study considérations relatives au régime des grandes eaux, au débouché à leur and took the lead of the project. RMP made a geological interpretation of the donner, et à la marche des alluvions dans les rivières à fond mobile data. TK discussed microtremor features. All authors read and approved the Government of Nepal (2015) Nepal disaster risk reduction portal. URL http:// final manuscript. www. drrpo rtal. gov. np/ Hashash Y, Tiwari B, Moss R, Asimaki D, Clahan K, Kieffer D, Dreger D, MacDon- Funding ald A, Madugo C, Mason B, Pehlivan M, Rayamajhi D, Acharya I, Adhikari This study was partially supported by the Grant-in-Aid for Scientific Research B (2015) Geotechnical field reconnaissance: Gorkha (Nepal) earthquake (A) “Extraction of hidden and unstable landslide masses and their risk assess- of April 25th 2015 and related shaking sequence. Geotechnical Extreme ment,” the Japan Society for the Promotion of Science, No. 16H02744 (Leader: Event Reconnaisance GEER Association Report No. GEER-040 Kazuo Konagai). Haskell NA (1953) The dispersion of surface waves on multilayered media. Bull Seismol Soc Am 43(1):17–34 Availability of data and materials Hatanaka M, Uchida A (1996) Empirical correlation between penetration resist- The datasets used and analyzed in this study are available and can be pro- ance and internal friction angle of sandy soils. Soils Found 36(4):1– vided by the corresponding author upon request. 9. https:// doi. org/ 10. 3208/ sandf. 36.4_1 Huat BB (2006) Deformation and shear strength characteristics of some tropi- cal peat and organic soils. Pertanika J Sci Technol 14(1–2):61–74 Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 15 of 15 JICA (2002) The study of earthquake disaster mitigation in the Kathmandu Gorkha (Nepal) earthquake. Eng Fail Anal 59:161–184. https:// doi. org/ 10. Valley, Kingdom of Nepal. Final Report I-IV1016/j. engfa ilanal. 2015. 10. 003 JICA (2015) The Project on Urban Transport Improvement for Kathmandu Val- Sharma K, Deng L (2016) Geotechnical engineering aspect of the 2015 Gorkha, ley in Federal Democratic Republic of Nepal. URL https:// openj icare port. Nepal Earthquake. In: Proceedings of the 1st international symposium on jica. go. jp/ pdf/ 12289 674. pdf soil dynamics and geotechnical sustainability Katel TP, Upreti BN, Pokharel GS (1996) Engineering properties of fine grained Sharma K, Subedi M, Parajuli RR, Pokharel B (2017) Eec ff ts of surface geology soils of Kathmandu Valley. J Nepal Geol Soc 13:121–138. https:// doi. org/ and topography on the damage severity during the 2015 Nepal Gorkha 10. 3126/ jngs. v14i0. 32401 earthquake. Lowl Technol Int 18:269–282 Kokusho T, Yoshida Y (1997) SPT N-value and S-wave velocity for gravelly soils Sharma K, Deng L, Khadka D (2019) Reconnaissance of liquefaction case stud- with different grain size distribution. Soils Found 37(4):105–113. https:// ies in 2015 Gorkha (Nepal) earthquake and assessment of liquefaction doi. org/ 10. 3208/ sandf. 37.4_ 105 susceptibility. Int J Geotech Eng 13:326–338. https:// doi. org/ 10. 1080/ Konagai K, Pokhrel RM, Matsubara H, Shiga M (2015) Geotechnical aspect of 19386 362. 2017. 13503 38 the damage caused by the April 25th. JSCE J Disaster FactSheets Subedi M, Acharya IP (2022) Liquefaction hazard assessment and ground Kyrieleis W, Sichardt W (1930) Grundwasserabsenkung bei fundierungsar- failure probability analysis in the Kathmandu Valley of Nepal. Geoenviron beiten. Julius Springer, Berlin Disasters. https:// doi. org/ 10. 1186/ s40677- 021- 00203-0 Lermo J, Francisco J (1994) Chávez-García; are microtremors useful in site Takai N, Shigefuji M, Rajaure S, Bijukchhen S, Ichiyanagi M, Dhital MR, Sasatani response evaluation. Bull Seismol Soc Am 84(5):1350–1364. https:// doi. T (2016) Strong ground motion in the Kathmandu Valley during the 2015 org/ 10. 1785/ BSSA0 84005 1350 Gorkha, Nepal, earthquake. Earth Planets Sp 68(1):1–8. https:// doi. org/ 10. Maharjan M (2017) Liquefaction in Kathmandu Valley during 2015 Gorkha 1186/ s40623- 016- 0383-7 (Nepal) earthquake. In: 16th World conference on earthquake engineer- Tiwari B, Pradel D, Ajmera B, Yamashiro B, Khadka D (2018) Landslide move- ing 16WCEE 2017 ment at Lokanthali during the 2015 earthquake in Gorkha Nepal. J Geo- McGowan SM, Jaiswal KS, Wald DJ (2017) Using structural damage statistics to tech Geoenviron Eng 144(3):05018001. https:// doi. org/ 10. 1061/ (ASCE) GT. derive macroseismic intensity within the Kathmandu valley for the 2015 1943- 5606. 00018 42 M7. 8 Gorkha, Nepal earthquake. Tectonophys 714-715:158–172. https:// Tokimatsu K, Miyadera Y (1992) Characteristics of Rayleigh waves in micro- doi. org/ 10. 1016/j. tecto. 2016. 08. 002 tremors and their relation to underground structures. J Struct Constr Eng Molnar S, Onwuemeka J, Adhikari S (2017) Rapid post-earthquake micro- 439:81–87 tremor measurements for site amplification and shear wave velocity Tsushima M, Oikawa H (1982) Shear strength and dilatancy of peat. Soils profiling in Kathmandu, Nepal. Earthq Spectra. https:// doi. org/ 10. 1193/ Found 22(2):133–141. https:// doi. org/ 10. 3208/ sandf 1972. 22.2_ 133 12191 6EQS2 45M USGS (2015) M7.8 Nepal Earthquake of 25 April 2015. http:// earth quake. usgs. Moss RE, Thompson EM, Kieffer DS, Tiwari B, Hashash YM, Acharya I, Adhikari gov/ earth quakes/ eqarc hives/ poster/ 2015/ Nepal Summa ry. pdf BR, Asimaki D, Clahan KB, Collins BD (2015) Geotechnical effects of the von Seht MI, Wohlenberg J (1999) Microtremor measurements used to map 2015 magnitude 7.8 Gorkha, Nepal, earthquake and aftershocks. Seismol thickness of soft sediments. Bull Seismol Soc Am 89(1):250–259. https:// Res Lett 86(6):1514–1523. https:// doi. org/ 10. 1785/ 02201 50158doi. org/ 10. 1785/ BSSA0 89001 0250 Nakamura Y (1989) A method for dynamic characteristics estimation of Wang F, Miyajima M, Dahal R (2016) Eec ff ts of topographic and geological subsurface using microtremor on the ground surface. Q Rep Railw Tech features on building damage caused by 2015.4.25 Mw7.8 Gorkha earth- Res Inst 30:25–33 quake in Nepal: a preliminary investigation report. Geoenviron Disasters OCHA (2015) Humanitarian Bulletin Nepal Earthquake Issue 04 (Final Issue). 3:7–7. https:// doi. org/ 10. 1186/ s40677- 016- 0040-2 URL: https://reliefweb.int/report/nepal/humanitarian-bulletin-nepal- Yasuda S, Hashimoto T (2016) New project to prevent liquefaction-induced earthquake-issue-04-final-issue-1-30-september-2015 damage in a wide existing residential area by lowering the ground water Okamura M, Bhandary NP, Mori S, Marasini N, Hazarika H (2015) Report on a table. Soil Dyn Earthq Eng 91:246–259. https:// doi. org/ 10. 1016/j. soild yn. reconnaissance survey of damage in Kathmandu caused by the 2015 2016. 09. 029 Gorkha Nepal earthquake. Soils Found 55(5):1015–1029. https://doi. org/10.1016/j.sandf.2015.09.005 Publisher’s Note Pandey M (2000) Ground response of Kathmandu valley on the basis of micro- Springer Nature remains neutral with regard to jurisdictional claims in pub- tremors. In: Proceedings of the 12th World Conference on Earthquake lished maps and institutional affiliations. Engineering. Parajuli RR, Kiyono J (2015) Ground motion characteristics of the 2015 Gorkha earthquake, survey of damage to stone masonry structures and structural field tests. Front Built Environ. https:// doi. org/ 10. 3389/ fbuil. 2015. 00023 Park C, Miller R, Xia J (1999) Multichannel analysis of surface waves (MASW ). Geophysics. https:// doi. org/ 10. 1190/1. 14445 90 Polito CP, Martin II JR (2001) Eec ff ts of non-plastic fines on the liquefaction resistance of sands. J Geotech Geoenviron Eng 127(5):408–415. https:// doi. org/ 10. 1061/ (ASCE) 1090- 0241(2001) 127: 5(408) Ram TD, Wang G (2011) Probabilistic seismic hazard analysis in Nepal. Earthq Engrg Engrg Vib 12:577–586. https:// doi. org/ 10. 3126/ jiee. v2i1. 36676 Rix GJ, Leipski EA (1991) Accuracy and resolution of surface wave inversion. In: Proceedings of recent advances in instrumentation, data acquisition and testing in soil dynamics Saito M (2006) Fast calculation of the Jacobian of surface wave phase velocity. Butsuri-Tansa/geophys Explor 59(4):381–388. https:// doi. org/ 10. 3124/ segj. 59. 381 Sakai H, Fujii R, Kuwahara Y, Noi H (2000) Climatic changes and tectonic events recorded in the Paleo-Kathmandu lake sediment. J Geogr 109(5):759– 769. https:// doi. org/ 10. 5026/ jgeog raphy. 109. 759 Sakai H, Fujii R, Sugimoto M, Setoguchi R, Paudel MR (2016) Two times lower- ing of lake water at around 48 and 38 ka, caused by possible earthquakes, recorded in the Paleo-Kathmandu lake, central Nepal Himalaya. Earth Planets Sp 68(1):1–10. https:// doi. org/ 10. 1186/ s40623- 016- 0413-5 Shakya M, Kawan CK (2016) Reconnaissance based damage survey of build- ings in Kathmandu valley: an aftermath of 7.8 Mw, April 25th 2015 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Investigation of ground fissures at Kausaltar, Kathmandu by in-situ testing and spatial geographical mapping

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Abstract

On April 25th, 2015, the Gorkha earthquake jolted the central region of Nepal, causing extensive damage to buildings and grounds in the urban areas of Nepal. One embankment section of Kathmandu-Bhaktapur Road, crosses a small valley in the center of the Kathmandu Basin. The earthquake has caused this embankment to deform with its support- ing soil. Investigating the mechanism of this ground deformation from the geotechnical and geological viewpoints was deemed necessary to examine possible countermeasures. For this purpose, we conduct several in-situ tests such as microtremor measurements, standard penetration tests, and Multichannel Analysis of Surface Waves. These investi- gations make two soft soil layers emerge as a causative factor. The estimated 3D soil profile shows that the deformed ground overlaps the area where the weak soil layers are below the groundwater level. The 3D soil profile also suggests that groundwater lowering using existing wells can reduce the water-saturated area by 81%. Carbon dating shows that the causative layer formed before the Paleo-Kathmandu Lake dried up. Keywords: 2015 Gorkha earthquake, Kathmandu, Ground fissures, Standard penetration test, Multichannel analysis of surface waves, Spatial ground model Introduction within the subduction interface between the Indian plate The 2015 Nepal earthquake (M = 7.8), also called the underneath the Eurasian plate. Gorkha earthquake, was the worst natural disaster to OCHA (2015) estimated the death toll and the prop- hit Nepal since the 1934 Nepal–Bihar earthquake. Its erty loss caused by the Gorkha earthquake at 8891 and epicenter was located at Barpak, Gorkha (28.231° N, $7.1 billion, respectively; the latter is almost equivalent 84.731° E), as shown in Fig.  1a. The earthquake rupture to the annual national budget in Nepal. The govern - extended about 100  km to the east of the epicenter at a ment of Nepal (2015) reported two-thirds of all inju- strike of 295° (USGS 2015). The most recent earthquake ries within the Basin. The number of partially damaged of the same magnitude was the Nepal-Bihar earthquake structures was more than 511,000 throughout Nepal, in 1934. Nasu (1935) reported that the intense ground of which roughly 75,000 are located in the Kathmandu shaking was the primary cause of complete and partial Basin. These reports suggest that rapid urbanization has collapses of many buildings in three major cities in Nepal, increased the threat of earthquakes in the Kathmandu namely Kathmandu, Bhatgaon, and Patan. These major Basin. earthquakes occurred immediately below the Himalayas Many researchers, such as Chiaro et al. (2015), Shakya and Kawan (2016), McGowan et  al. (2017), and Wang et  al. (2016), described the structural or ground damage *Correspondence: shiga815@iis.u-tokyo.ac.jp in the Kathmandu Basin as follows; Institute of Industrial Science, Be-206, The University of Tokyo, 4-6-1, Komaba, Meguro, Tokyo 1538505, Japan Full list of author information is available at the end of the article © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 2 of 15 Fig. 1 Survey locations and local topography with ground offsets that appeared in Kausaltar and measurement by several investigation teams (Konagai et al. 2015; JICA 2015; Angster et al. 2015) a Entire Map with digital terrain model from JAXA b Regional Map with digital terrain model from JAXA c Local Map with overlaid on an aerial image from Google Earth Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 3 of 15 – The degree of building damage becomes more signifi - 10% probability of exceedance PGA within 50 years esti- cant toward the basin center. For example, the his- mated by JICA (2002) or Ram and Wang (2011). They torical architecture around Durbar Square (Fig.  1b) also pointed out that the local earthquake amplification suffered from complete collapse. In contrast, the characteristics of the Basin may have caused damage to damage to residential buildings was relatively low buildings. despite the fragility of common masonry structures. The thick lacustrine soil deposit is perhaps responsi - – Liquefaction traces were found at various locations, ble for long-period seismic motions. A deep borehole such as Jharuwarashi, Bungamati, and Nepal Engi- log obtained by Sakai et al. (2000) shows that a weak clay neering College, but damage to structures due to liq- layer called Kalimati formation lies between 15 and 40 m uefaction was limited. in depth. A series of magnetostratigraphic and paleonto- logical observations by Katel et  al. (1996) revealed that lacustrine formations stacking one on the other could be Several research reports pointed out that basin-spe- 600  m thick in the Basin. Sakai et  al. (2016) conducted cific seismic motion has caused damage to structures. a thorough sedimentary survey and carbon dating to For example, Takai et  al. (2016) obtained strong ground investigate several water-lowering events that geologists motions at one rocky site and three sedimentary soil believe occurred in the Paleo-Kathmandu Lake. They sites in the Kathmandu Basin and compared them with reported that although the cause of the lowering is still the seismic record at the USGS KATNP Station (USGS, unclear, there were at least two significant decreases in 2015), as shown in Fig.  1b. They found that horizontal the lake water level. They also concluded that the Paleo- components of long-period oscillation had substantial Kathmandu Lake dried up about 12,000 years ago. power to damage high-rise buildings at the sedimentary Although the ground in the other area of the Kath- soil site, as shown in Fig.  2. Some other papers, such as mandu Basin rarely deformed, a severe ground displace- Parajuli and Kiyono (2015), Bijukchhen et al. (2017), and ment occurred at Kausaltar, about 2  km southeast of Wang et  al. (2016), reported that long-period seismic Tribhuvan International Airport. Some cracks and fis - motions of 1 to 2 s were observed in the mainshock and sures as long as 400  m maximum appeared on a gently aftershocks, and these tremors mainly caused damage sloping alluvial hill. This paper discusses when the causa - to low-rise structures in the Kathmandu Basin. Sharma tive layers have formed, how the ground has deformed, et  al. (2017) showed that the PGA did not exceed the Fig. 2 Observed ground accelerations at one rock site (KTP), three sedimentary sites ( TVU, PTN, and THM) by Takai et al. (2016), and one sedimentary site (KATNP) by USGS (2015) (Reprinted from Takai et al. (2016)) Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 4 of 15 and future potential ground hazards through several in- situ testings, carbon dating, and GIS mapping. Study area Kausaltar (27.6745° N, 85.3607° E), about 2  km southeast of the Tribhuvan International Airport of Kathmandu, is a residential area spreading over ter- races constituting the upper part of the sedimentary sequence of the Kathmandu Basin (Fig.  1c). An about 500 m embankment section of the Kathmandu-Bhakta- pur Road, a part of Araniko Highway, crosses a small shallow swampy valley in the Basin diagonally. 200– 400  m long fissures associated with vertical ground offsets appeared diagonally across this road (Konagai et al. 2015). These fissures ran almost parallel, trending in NEE to SWW direction and slightly bent to the east after crossing the road. These fissures associated with Fig. 3 A sand-filled fissure that appeared on a wall of Trench-1 excavated by Angster et al. (2015) vertical offsets indicate that the soil mass on the north - western slope slumped as a whole and moved slightly towards the shallow and swampy valley, which runs Subedi and Acharya (2022) calculated the factor of almost parallel to these fissures. The most extended safety against liquefaction in the Kathmandu Basin and crack bordering the southeastern end of the deformed reported that the factor of safety around Kausalter was area was accompanied by the most prominent vertical less than 0.5 during the 2015 mainshock. offset reaching 2  m. Other shorter fissures appeared on the other side of the valley. Both sides of the val- Objective and methodology ley seem to have moved against each other, causing the Previous studies have presented important clues for middle part of the Highway section to be slightly bent discussing the causes of this ground deformation; the upwards. At the same time, only minor damage was clues include sand-filled fissures, the presence of shal - observed in the reinforced retaining walls and the earth low organic soil layer or clayey soil, etc. However, they embankment of Kathmandu-Bhaktapur Road (Sharma just provided us with information point-wise and did and Deng 2016). not consider the historical sedimentary environment in There are various theories for the cause of this ground Kausaltar. To cover a much wider extent of the deformed deformation in Kausaltar discussed by many research- ground and clarify how the causative layer formed, we ers. Sharma et  al. (2019) and Okamura et  al. (2015) conducted the following in-situ tests; reported a 2-m deep fissure associated with an about 1.5-m vertical scarp. Sharma et  al. (2019) have raised 1. Microtremor measurements, two causative soils: a lacustrine clay called Kalimati 2. Multi-channel analysis of surface wave (MASW), Clay and liquefiable sand. Angster et  al. (2015) exca - 3. Standard penetration test (SPT), vated a 2.5  m deep trench across the scarp and found 4. Real-Time kinematic global navigation satellite sys- a sand-filled fissure on the trench wall (Fig.  3). Moss tem survey (RTK-GNSS survey), and. et  al. (2015) first thought the causative soil was Kali - 5. Carbon dating. mati Clay. But seeing thin planner intrusions of sand exposed on the trench wall, they finally deduced the Integrating the obtained data sets on GIS, we created causative soil was the liquefiable sand. Maharjan (2017) a 3D hydrogeological model for the shallow part of the attributed the lateral spreading to cyclic shear soften- lacustrine soil deposit of Kausaltar. The groundwater ing of a silty clay lacustrine deposits. He also reported level and two soil layers were estimated through Inverse that a resident witnessed that the fissures had devel - Distance Weighting (IDW, hereafter). In addition, we oped longer and deeper during the Mw6.7 aftershock assumed an axisymmetric pumping model in a homoge- on May 12th, 2015. Tiwari et  al. (2018) conducted in- neous soil to discuss the effect of lowering the groundwa - situ sounding tests and numerical analyses. They found ter level through temporary wells. This section describes that the lacustrine clayey deposits had deficient shear these methods in detail. strength and were highly vulnerable to slope instability. Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 5 of 15 Microtremor measurement C (ω) = U (ω)U (ω) ij i j We conducted microtremor measurements in Kausal- tar and the downtown area of Kathmandu near the USGS where, U (ω) and U (ω) are Fourier Spectra of u (t) and i j i KATNP station at 27.7124° N, 85.3156° E. A seismometer u (t) , resp e ctively . (CV-374AV, Tokyo Sokushin Co. Ltd.) measures the three The phase components of this cross-spectrum C (ω) ij orthogonal components of the ambient ground motion. The are precisely the phase differences at all frequencies range of frequencies that this seismometer can record is between the two points i and j. u Th s, given C (ω) , we ij from 0.1 to 100 Hz. We measured ambient ground motions obtain the dispersive nature of the Rayleigh wave, and we at 7 points on the deformed ground on the northwestern can back-analyze the stiffness profile of the layered soil side of the Highway (BH-1 and BH-3 ~ 8 in Fig. 1c), 3 points medium (Haskell 1953 or Saito 2006). on the adjacent intact ground (BH-9, MT-1, and MT-2 in Fig. 1c), and 4 points next to the KATNP observatory. Standard penetration test We calculated the spectral ratios between the ambi- We conducted Standard Penetration Tests (SPT) at five ent ground motion’s horizontal and vertical components boreholes, BH-5, BH-6, BH-7, BH-8, and BH-9, follow- (H/V ratios) at these points by applying the 0.05  Hz ing JIS A1219 (Japan Standards Association 2013), in Parzen window in the frequency domain. The ratios are December 2016 and April 2017. Besides them, the Japan independent of the source distance and significantly con - International Agency (JICA 2015) drilled four more tribute to the site-specific effect evaluation. boreholes as a part of its rapid recovery project in August Nakamura (1989), Tokimatsu and Miyadera (1992), and 2015. At each borehole, a thick-walled sample tube was Lermo and Francisco (1994) considered that the H/V driven down by blows from a slide hammer with a mass ratio could be related to the ellipticity ratio of Rayleigh of 63.5 kg falling through a height of 760 mm. The sam - waves representing the intrinsic nature of the underly- pler is first driven to a depth of 15 cm below the bottom ing layered soil medium. When impedance contrasts of the pre-bored hole. Then, we count the blows (SPT-N between the soft surface soil and the underlying stiff bed value) required for the second, third and fourth 10 cm of stratum, a clear peak in the H/V spectral ratio can appear penetration. Previous studies have shown that the SPT-N at the natural frequency of the layered soil medium value can correlate with physical parameters such as (Tokimatsu and Miyadera 1992). The observation can shear wave velocity (Kokusho and Yoshida 1997), density explain this trend in that the horizontal component (H ) (Cubrinovski and Ishihara 1999), and internal friction reflects the response characteristics of the layered soil angle (Hatanaka and Uchida 1996). medium. In contrast, the vertical component (V ) retains the vibration characteristics of the bed stratum. Carbon dating Carbon dating is a method that provides objective age Multi‑channel analysis of surface waves estimates for carbon-based materials that originated Multi-channel Analysis of Surface Waves (MASW) was from living organisms. We have taken organic soil sam- performed along two lines (Lines 1 and 2 in Fig.  1c) on ples from various depths of the three boreholes (BH-7, the deformed ground to evaluate the shear wave velocity BH-8, and BH-9 in Fig. 1c) and the surface of a cut slope (v ) profile of the shallow layered soil. Lines 1 and 2 are (Fig.  1c), which was by chance excavated to construct a 72  m and 208  m long, respectively. The equipment used retaining wall near the shallow swampy valley. in this study, McSEIS-SW, OYO Corporation, allows us to There are three radioisotopes in carbon atoms; C, obtain an underground 2D Surface wave velocity struc- 13 14 C, and C. Scientists estimate that the ratio of these ture. The 24-bit resolution equipment records the ground radioisotopes in the atmosphere is almost constant, tremor at the minimum time interval of 0.0625 ms. –10 98.9:1.1:1.2 × 1.0 , because of the nitrogen formation The phase velocity of the Rayleigh wave that trav - by cosmic ray collisions and the beta decay of C itself. els horizontally through a layered soil medium dif- However, when samples move to an environment unaf- fers from frequency to frequency. Namely, the Rayleigh fected by cosmic rays, the percentage of C decreases. wave’s phase velocity dispersive nature reflects the lay - u Th s, knowing the C half-life of 5730 ± 40 years, we can ered structure of the soil medium. Following the algo- estimate when the organism died. rithm developed by Park et  al. (1999), we first compare We collaborated with the dating laboratory at the each pair of the ground tremor signals in the frequency University of Tokyo Museum. The samples were first domain through the cross-spectral density (CSD) analy- immersed in hydrochloric acid to remove contaminants sis. The cross-spectrum C (ω) of any arbitrary pair of ij and fulvic acid. Secondly, their carbon contents were ground tremor signals u (t) and u (t) is given by: i j Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 6 of 15 measured. When the measured carbon content exceeded common to carry out 3D seepage flow analysis. How - 10%, the carbon dioxide was vacuum-sealed with copper ever, due to remaining uncertainties in the underground oxide and sulfide in a double-sealed quartz glass tube and hydrological parameters, this study performed a pseudo- heated in an electric furnace to 850  °C for 3  h. Thirdly, 3D analysis using a much simpler model by Dupuit the carbon dioxide was purified using a vacuum line. The (1863). The basic formulation is as follows; collected carbon dioxide was then sealed inside a furnace R 2πh k tube with an iron catalyst and hydrogen and was reduced log = (H − h) r Q to carbon by heating the furnace tube at 650  °C for 6  h. Finally, we used an accelerator-mass-spectrometer to where R is the radius of the influence circle, r is the detect the amount of radioactive carbon. radius of a well, h is the thickness of a causative perme- able layer, k is the permeability coefficient, Q is the dis- RTK GNSS measurement charge from the well, H is the height of the static water To treat the in-situ geotechnical test results at each loca- table from the well bottom, and h is the height of water in tion as spatial information in GIS, highly accurate location the well from the well bottom. The radius of the influence information is required. Therefore, we measured latitude circle was calculated by using the empirical equation by and longitude by RTK (Real-Time Kinematic) positioning Kyrieleis and Sichardt (1930); using GNSS (Global Navigation Satellite System). GNSS is a method to determine the positional coordinates of a receiv- R = 3000s k ing station by launching several satellites into orbit. Each sat- where s is the amount of lowering and equal to H − h . ellite transmits radio waves containing the timing and orbital Based on Creager et  al. (1945), the permeability coeffi - information of the satellite. The receivers then use this data cient k is empirically given by; to determine location. RTK positioning is one of the GNSS- based interferometric positioning methods. It determines 2.2954 k = 0.0034(D ) the position coordinates by simultaneously receiving radio waves from satellites at base and rover stations to remove with D (mm) as the particle size for which 20% of the common errors such as multipath and satellite clock devia- material is finer. tion. RTK-GNSS enables us to determine locations vertically and horizontally with an accuracy of a few centimeters. Results and discussion Vibration characteristics Inverse distance weighting (IDW) Figure  4 shows the H/V spectral ratio obtained at each We use IDW as a spatial interpolation method given scat- location. This figure indicates that all H/V spectral ratios tered locations on the ground with known measured val- show relatively large values in a frequency range lower ues to estimate values at other unknown points. IDW than 1 Hz. As seen in Molnar et al. (2017); Pandey (2000), is easier to use than the Kriging method because IDW the relatively low dominant frequency may reflect the pres - employs a simple formula to calculate unknown values ence of a thick lacustrine deposit in the Paleo-Kathmandu at the prediction location. On the other hand, unlike the Lake. However, nothing shown in Fig.  4 seems to assure Kriging method, IDW does not assume a probability distri- the difference between the deformed and intact grounds. bution, and therefore, the estimation error is not available. Table 1 shows the dominant frequency of microtremor The value y(x) at a prediction location, x is calculated by at each location. As discussed in von Seht and Wohlen- available values y(x ) at known points x ( i = 0, 1, . . . , N ) i i berg (1999) and Delgado et  al. (2000), the spectral ratio as follows; has also been used to characterize qualitatively the sub- surface structure, especially the thickness of soft sedi- w (x)y(x ) i i i=0 ments. In a simplified two-layer ground structure, the y(x) = w (x) j wavelength of the shear wave at the lowest vibration j=0 mode, assuming the lower base layer as its fixed end, where, equals 1/4 of the layer thickness of the soft ground layer, L . Therefore, the dominant frequency f can be given by; s d w (x) = |x − x | s f = 4L One‑dimensional pumping model where v is the shear wave velocity of the upper soft When discussing the amount of pumping water or effec - ground layer. Table  1 shows that BH-1, BH-3, and BH-8 tive stress due to lowering the groundwater level, it is have relatively low dominant frequencies among the Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 7 of 15 Fig. 4 Microtremor H/V spectra at the observation sites in the undeformed area, the less-deformed area in Kausaltar, and near the KATNP observatory frequency shows that the softer surface layers are Table 1 Dominant frequency at the observation sites thicker or have smaller v as we come closer to the High- Deformed area Less deformed area Referenced area way. However, since the dominant frequencies near the Name Dominant Name Dominant Name Dominant KATNP observatory are roughly the same, we cannot frequency frequency frequency argue the damage extent based only on those frequencies. BH-1 0.16 BH-9 0.34 USGS-1 0.18 Figure  5 compares the variation of amplitude ratio in BH-3 0.59 MT-1 0.29 USGS-2 0.15 the frequency domain with the average Fourier spectrum BH-4 0.15 MT-2 0.52 USGS-3 0.21 of microtremors near the KATNP observatory as the reference. The red and black lines are for the deformed BH-5 0.56 USGS-4 0.26 and intact grounds in Kausaltar, respectively. The spike BH-6 0.33 that appears at 40  Hz is probably due to an unexpected BH-7 0.54 external or internal noise of the seismograph. It is per- BH-8 0.20 haps premature to deduce the essential nature of the ground at Kausaltar only from Fig.  5 without knowing measured locations in the deformed area. These points the real picture of the source of ambient microtremors are close to the eastern or western slopes of the High- in the Basin. However, compared with the area near the way, where the worst damage was. The low dominant Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 8 of 15 5.0 BH-3 Horizontal Components BH-3 Vertical Components 4.0 MT-2 Horizontal Components MT-2 Vertical Components 3.0 2.0 1.0 0.0 0.11 10 Freqency(Hz) Fig. 5 Variation of frequency-domain amplitude ratio at BH-3 and MT-2 with the Fourier spectrum of the microtremor observed at USGS-3 as the reference Fig. 6 Spatial distribution of v obtained through Multichannel Analysis of Surface Waves Subsurface soil profile KATNP observatory, the ground at Kausaltar is more Spatial distribution of shear wave velocity easily shaken over the frequency range larger than 5 Hz. Line 1 and Line 2 in Fig.  1c cross several ground fis - This tendency is more apparent in the seriously deformed sures diagonally. Figure  6 shows the estimated spatial area. Ratio between the Fourier spectra of ambient ground motions at Kausaltar and USGS KATNP observatory Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 9 of 15 distribution of shear wave velocity. The blue color shows peat and organic soils tend to have lower internal friction higher shear wave velocity values, while the red color angles at the same density. Tsushima and Oikawa (1982) shows lower shear wave velocity values. reported that undrained shear strength decreases with Rix  and Leipski (1991) concluded that the best over- increasing moisture content. Thus, the relative height of all accuracy and resolution in spectral analysis of sur- the organic soil layer to the groundwater level can indi- face waves was obtained when the maximum wavelength cate whether it softened or not. is one to two times the maximum desired depth of the A silty sand layer with almost the same v value as the shear wave velocity profile. Based on the above conclu - deeper low v layer was identified at 4–8  m beneath the sion, Park et  al. (1999) recommended using the half- ground surface. Some part of this layer was below the wavelength (maximum offset of seismic sensors) as a aquifer level. Several samples containing very thin tabu- reasonable depth. Therefore, the measurable depth in this lar sand-filled fissures were found, suggesting the pres - survey is about 12  m. The inverse analysis of the shear ence of a liquefiable layer beneath them. Many laboratory wave velocity profile is usually performed using the ini - tests show that liquefaction resistance is reduced when tial estimation for the ground depth of about one-third the soil’s non-plastic content is high (Polito and II 2001; of the wavelength. We made the initial estimation from Carraro et al. 2003). Therefore, the relative position of the the SPT-N values at the nearby boreholes. The initial soft layer to the groundwater level is vital in determining estimates of the shear-wave-velocity profile from differ - the causative layer. ent sets of SPT-N values can cause the final assessment of the velocity profile to differ, particularly for the deeper GIS analysis ground. We have deduced the upper surfaces of the above-men- Looking at the shallow part of the ground in Fig.  6, a tioned organic layer, the silty sand layer, and the ground- low v zone (1) spreads 3 to 5  m underground over the water level using the IDW method. The organic soil entire stretch of both Line 1 and 2. The value of v is layer lies mainly on the valley’s eastern slope, crossed around 140 m/s at 2 to 4 m below the ground surface in by the Highway (BH-7, 8, and 9). Part of the organic soil Line 1. The borehole (BH-5), projected on Line 1 as the also appears on the surface of the western valley slope, arrow in Fig.  6, is located almost on the extension of the where we took samples for carbon-dating. However, the fractures. The estimated soil profile along Line 1 shows deduced 0.5 m to 1 m thick organic soil layer is not seem- that v is greater than 180 m/s over 5 to 8 m depths along ingly causative because the organic layer lies above the the borehole. In contrast, a shallower and softer soil layer deduced groundwater surface (Fig. 8b). Moreover, exten- with v =160  m/s spread towards the valley side from sive fissures appeared even in the area where we found the borehole. A low shear wave velocity layer of 110 to no organic soil layer in BH-5 and BH-6. It is thus unlikely 130  m/s lies at 2 to 4  m below the ground surface along that this soil layer is responsible for the extensive lateral Line 2 in Fig.  6. One more slightly lower shear wave spreading. velocity layer of 140  m/s at 5 to 8  m below the ground The height difference between the upper surface of the surface straddles the two significant fractures. These aquifer and the lower surface of the silty sand layer was two soft layers can be considered possible causes of the obtained at each borehole in the target area, and spatial fissures. variation of the height difference was deduced as shown in Fig.  8b. It stands out that the orange area where the SPT silty sand beneath the aquifer overlaps the area of fis - Figure  7 shows the soil classifications and SPT N-value sures associated with vertical ground offsets (white lines). distributions for all boreholes. SPT N-value can be cor- Though the aquifer level may fluctuate occasionally, this related with the hardness of the soil. N-values are at most fact strongly suggests that the deeper silty sand layer ten over the almost entire stretches of BH-7, BH-8, and beneath the aquifer could have been the primary cause of BH-9. These boreholes are closer to the swampy val - the lateral spreading. ley than the others. Groundwater levels in BH-5, BH-6, BH-7, and BH-8, shown by broken blue lines in Fig.  7, Possible countermeasure lie between 4.4 and 7.3  m underground. We found no To prevent the water-saturated silty sand layer from groundwater table in BH-9. softening in a future earthquake, we propose ground- We also found organic soils above the groundwater water lowering using locally available wells as a practi- level from the extracted core samples. The depths of cal measure. The Google Earth satellite image obtained these organic soils were consistent with the depths of on November 11th, 2015, shows 70 houses in the the upper low v layers. Several research reports, such deformed area; all these houses presumably have wells. as Huat (2006) and Blanco-Canqui et  al. (2005), showed We also assume that 14 extra wells will be excavated in Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 10 of 15 Fig. 7 Soil classifications and SPT N-value distributions at 5 boreholes. Blue dotted lines show the initial water level of each borehole after reaching that depth open spaces. Figure  9 again shows the height difference consolidation. For example, Yasuda and Hashimoto between the upper surface of the aquifer and the lower (2016) reported that the maximum subsidence of 7.8 cm surface of the silty sand layer. In this figure, however, was reached in Japan due to groundwater pumping as a the upper surface of the aquifer is assumed to be 1.75 m measure against liquefaction. The sandy soil layer sus - higher than what we observed to be on the safe side of pected to have liquefied in the earthquake contains fine the discussion, considering the seasonal fluctuation of substances, which may cause slow dissipation of excess the aquifer level. pore water pressure and thus require more time to set- As shown in Fig.  10, when 4.2  m /day of water is tle. Further studies will be required to implement this withdrawn at each well, the area overlying the water- measure. 4 2 saturated silty sand layer decreases from 2.9 × 10  m to 3 2 5.6 × 10  m . Carbon dating Lowering the groundwater level is an effective way to Carbon dating revealed that organic soil lies around increase effective stress in soils and reduce the likeli - 1.9  m, 5.5  m to 6.0  m, and 3.0  m beneath the ground hood of liquefaction occurrence. However, it has some surface at BH-7, BH-8, and BH-9. Table  2 shows the disadvantages, such as ground subsidence due to soil depths of the organic soils, the calibrated soil ages, and Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 11 of 15 Fig. 8 Difference between the upper surface of the aquifer and the upper surface of two suspicious layers in Kausaltar. a Organic layer b Silty sand layer Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 12 of 15 Fig. 9 Difference between the upper surface of the aquifer and the lower surface of the silty sand layer in Kausaltar (before lowering groundwater level) the estimation errors. Figure 11 also shows the calibrated caused an embankment section of the Kathmandu- ages of the organic soil samples and their elevations. Bhaktapur Road (Highway) to deform with its support- The estimated age varies from BC 9,300 to BC 13,100. ing soil. Extensive 200–400  m long fissures traversed These periods overlap when the Paleo Kathmandu Lake the embankment diagonally, and the ground spread has been drying around BC 10,500 (Sakai et  al. 2016). laterally toward a shallow swampy valley. We have Several samples were taken at different depths along conducted field surveys and studied the potentially BH-8 and BH-9. The shallower the samples are, the older causative factors. Here are the conclusions: are the estimated ages. Perhaps, it is because shallower carbon-fixing flora exposed to air earlier than deeper 1. H/V ratios obtained at several points near the dam- flora as the Paleo-Kathmandu Lake dried up. The result aged Highway embankment exhibited peaks at low suggests that the strata below the organic soil layers, such frequencies. They suggested that the soft surface as the causative silty soil, were significantly influenced by layer can be thicker as we come closer to the High- the initial depositional environment of the Paleo Kath- way. mandu Lake. Strata with similar mechanical properties 2. Multi-channel Analysis of Surface Waves showed may spread wide in the Kathmandu Basin. the presence of two soft soil layers. One spreads 2 to 4  m underground over the entire stretch of the tar- get area, while the other spreads 5  m underground, Conclusion mainly on the lower side of the swath of ground fis - The 2015 Gorkha earthquake caused extensive damage sures. Standard Penetration Tests (SPT) also revealed in the rugged mountain areas and the flat Kathmandu the presence of two weak layers; a shallower weak Basin. The collapse of masonry structures and local - organic soil layer 2 to 5 m deep and a deeper soft silty ized soil liquefaction featured the damage reported sand layer 5 to 8 m deep beneath the ground surface. in the Basin. Among them, the ground deforma- tion near Kausaltar was unique. The earthquake has Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 13 of 15 Fig. 10 Difference between the upper surface of the aquifer and the lower surface of the silty sand layer in Kausaltar (After lowering groundwater level) Table 2 Obtained ages of organic soils found at BH-7, BH-8, BH-9, and the cut slope Name Depth (m) Calibrated age ± Error (BC) Cut slope 9751 294 BH-7 − 1.83 ~ − 1.90 9538 217 BH-8 − 5.32 ~ − 5.44 10,583 108 − 5.43 ~ − 5.50 10,215 211 − 5.65 ~ − 5.78 10,042 157 − 5.81 ~ − 5.97 11,181 65 BH-9 − 2.84 ~ − 3.00 12,815 309 − 3.20 ~ − 3.40 10,364 203 Fig. 11 Relation diagram between calibrated age and elevation of organic soil sample 3. The deeper silty sand layer beneath the aquifer over - laps the area of lateral spreading associated with extensive fissures. Though the aquifer level may fluc - could have formed when the Paleo-Kathmandu Lake tuate occasionally, this fact strongly suggests that the was drying up. Thus, weak soil layers like those found deeper silty sand layer beneath the aquifer could have at Kausaltar can spread wide in the Kathmandu been the primary cause of the lateral spreading. Basin. 4. Carbon dating for organic soil samples taken from boreholes indicated that these organic soil layers Shiga et al. Geoenvironmental Disasters (2022) 9:11 Page 14 of 15 Declarations The third finding suggests that groundwater lowering using locally available wells will increase effective stress Competing interests in soils and thus reduce the likelihood of liquefaction The authors declare that they have no competing interests. occurrence in future earthquakes. This measure may Author details cause some side effects, such as ground subsidence due Institute of Industrial Science, Be-206, The University of Tokyo, 4-6-1, Komaba, to soil consolidation. Further studies will be required to Meguro, Tokyo 1538505, Japan. International Consortium on Landslides, 138-1, Tanaka-Asukai, Kyoto, Sakyo 6068226, Japan. Ear th I nvestigation figure out if this measure is feasible. and Solution, Nepal Pvt. Ltd, Kirtipur-2, Kathmandu, Nepal. Depar tment of Civil and Environmental Engineering, 805, Building No.1 of Mechanical Con- struction, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, List of symbols Niigata 9402188, Japan. SPT: Standard penetration test; MASW: Multi-channel analysis of surface wave; KATNP: Kathmandu, Nepal observatory of the United States geological survey; Received: 1 October 2021 Accepted: 3 May 2022 JICA: Japan international cooperation agency; USGS: United States geologi- cal survey; OCHA: United Nations office for the coordination of humanitarian affairs; PGA: Peak ground acceleration; GIS: Geographic information system; RTK-GNSS: Real-time kinematic global navigation satellite system; IDW: Inverse distance weighting; BH: Borehole; JIS: Japanese institute of standards; u (t): References Horizontal displacement; u (t): Vertical displacement; t : Time; u (t): Displace- v x Angster S, Fielding EJ, Wesnousky S, Pierce I, Chamlagain D, Gautam D, Upreti ment in x-axis direction; u (t): Displacement in y-axis direction; : Frequency; y f BN, Kumahara Y, Nakata T (2015) Field reconnaissance after the April 25th : Horizontal fourier spectrum; : Vertical fourier spectrum; : Dis- H(f ) V (f ) u (f ) 2015 M 78 Gorkha earthquake. Seismol Res Lett 85:1506–1513 placement at point i; : Fourier spectrum at point i; : Cross-spectrum C (f ) U (f ) ij Association JS (2013) JIS A1219:2013 Method for standard penetration test. of point i and point j; x: Position vector; y(x): Scalar physical quantity at Bijukchhen S, Takai N, Shigefuji M, Ichiyanagi M, Sasatani T (2017) Strong position x; w(x): Weight by distance; R: Radius of influence circle; r : Radius of motion characteristics and visual damage assessment around seismic well; h : Thickness of a causative permeable layer; k: Permeability coefficient; : 0 Q stations in Kathmandu after the 2015 Gorkha, Nepal earthquake. Earthq Discharge from well; H: Height of static water table from well bottom; h: Height Spectr 33(1_suppl):219–242. https:// doi. org/ 10. 1193/ 04291 6eqs0 74m of water in the well from well bottom; s: Amount of lowering; D : Particle size Blanco-Canqui H, Lal R, Owens LB, Post WM, Izaurralde RC (2005) Strength for which 20% of the material is finer.; : Dominant frequency; v : Shear wave f s properties and organic carbon of soils in the North Appalachian region. velocity; L : Layer thickness of the upper soft ground layer. Soil Sci Soc Am J 69(3):663–673. https:// doi. org/ 10. 2136/ sssaj 2004. 0254 Carraro JAH, Bandini P, Salgado R (2003) Liquefaction resistance of clean and Acknowledgements non-plastic silty sands based on cone penetration resistance. J Geotech The author’s special thanks go to Mr. Masashi Ogawa, Mr. Shinya Machida, and Geoenviron Eng 129(11):965–976. https:// doi. org/ 10. 1061/ (ASCE) 1090- Mr. Makoto Oyama, at the Embassy of Japan, Kathmandu, Nepal. We would 0241(2003) 129: 11(965) also like to thank Professor Tara Nidhi Bhattarai, and Prof. Danda Pani Adhikari, Chiaro G, Kiyota T, Pokhrel RM, Goda K, Katagiri T, Sharma K (2015) Reconnais- Department of Geology, Tribhuvan University, for sharing valuable information sance report on geotechnical and structural damage caused by the 2015 on the local situation. Our thanks also go to Dr. Akira Nakamura, Mr. Kazuki Gorkha earthquake, Nepal. Soils Found 55(5):1030–1043. https:// doi. org/ Shimada, and Mr. Sanumasa Kazui, Infrastructure and Peacebuilding Depart- 10. 1016/j. sandf. 2015. 09. 006 ment, Japan International Cooperation Agency, who have kindly provided Creager WP, Justin JD, Hinds J (1945) Earth, rock-fill, steel and timber dams. Eng the authors with essential pieces of information regarding damage caused by Dams III:648–649 the 2015 Gorkha Earthquake as well as every convenience for field surveys. Cubrinovski M, Ishihara K (1999) Empirical correlation between SPT N-value Furthermore, we wish to acknowledge Dr. Minoru Yoneda, Dr. Takayuki Omori, and relative density for sandy soils. Soils Found 39(5):61–71. https:// doi. and Mr. Hiromasa Ozaki, Laboratory of Radiocarbon Dating, The University org/ 10. 3208/ sandf. 39.5_ 61 of Tokyo, for providing us with ages of soil samples containing soil samples Delgado J, Casado CL, Giner J, Estevez A, Cuenca A, Molina S (2000) Micro- organic matters through carbon dating. The authors also would like to express tremors as a geophysical exploration tool: applications and limitations. their sincere gratitude to Mr. Shogo Aoyama for conducting the borehole Pure Appl Geophys 157(9):1445–1462. https:// doi. org/ 10. 1007/ PL000 drilling and physical tests. Finally, the authors wish to thank the tremendous help given by Dr. Alessandra Mayumi Nakata Kaiami, Mr. Hikaru Tomita, and Dunod Gautam D, de Magistris FS, Fabbrocino G (2017) Soil liquefaction in Mr. Bhandari Basant in the field investigations. Kathmandu valley due to April 25th 2015 Gorkha, Nepal earthquake. Soil Dyn Earthq Eng 97:37–47. https:// doi. org/ 10. 1016/j. soild yn. 2017. 03. 001 Author contributions Dupuit J (1863) Études théoriques et pratiques sur le mouvement des eaux MS analyzed and interpreted all of the site-investigation data regarding the dans les canaux découverts et à travers les terrains perméabls: avec des borehole log and microtremors. KK showed the overall direction of the study considérations relatives au régime des grandes eaux, au débouché à leur and took the lead of the project. RMP made a geological interpretation of the donner, et à la marche des alluvions dans les rivières à fond mobile data. TK discussed microtremor features. All authors read and approved the Government of Nepal (2015) Nepal disaster risk reduction portal. URL http:// final manuscript. www. drrpo rtal. gov. np/ Hashash Y, Tiwari B, Moss R, Asimaki D, Clahan K, Kieffer D, Dreger D, MacDon- Funding ald A, Madugo C, Mason B, Pehlivan M, Rayamajhi D, Acharya I, Adhikari This study was partially supported by the Grant-in-Aid for Scientific Research B (2015) Geotechnical field reconnaissance: Gorkha (Nepal) earthquake (A) “Extraction of hidden and unstable landslide masses and their risk assess- of April 25th 2015 and related shaking sequence. Geotechnical Extreme ment,” the Japan Society for the Promotion of Science, No. 16H02744 (Leader: Event Reconnaisance GEER Association Report No. GEER-040 Kazuo Konagai). Haskell NA (1953) The dispersion of surface waves on multilayered media. Bull Seismol Soc Am 43(1):17–34 Availability of data and materials Hatanaka M, Uchida A (1996) Empirical correlation between penetration resist- The datasets used and analyzed in this study are available and can be pro- ance and internal friction angle of sandy soils. Soils Found 36(4):1– vided by the corresponding author upon request. 9. https:// doi. org/ 10. 3208/ sandf. 36.4_1 Huat BB (2006) Deformation and shear strength characteristics of some tropi- cal peat and organic soils. Pertanika J Sci Technol 14(1–2):61–74 Shiga  et al. Geoenvironmental Disasters (2022) 9:11 Page 15 of 15 JICA (2002) The study of earthquake disaster mitigation in the Kathmandu Gorkha (Nepal) earthquake. Eng Fail Anal 59:161–184. https:// doi. org/ 10. Valley, Kingdom of Nepal. Final Report I-IV1016/j. engfa ilanal. 2015. 10. 003 JICA (2015) The Project on Urban Transport Improvement for Kathmandu Val- Sharma K, Deng L (2016) Geotechnical engineering aspect of the 2015 Gorkha, ley in Federal Democratic Republic of Nepal. URL https:// openj icare port. Nepal Earthquake. In: Proceedings of the 1st international symposium on jica. go. jp/ pdf/ 12289 674. pdf soil dynamics and geotechnical sustainability Katel TP, Upreti BN, Pokharel GS (1996) Engineering properties of fine grained Sharma K, Subedi M, Parajuli RR, Pokharel B (2017) Eec ff ts of surface geology soils of Kathmandu Valley. J Nepal Geol Soc 13:121–138. https:// doi. org/ and topography on the damage severity during the 2015 Nepal Gorkha 10. 3126/ jngs. v14i0. 32401 earthquake. Lowl Technol Int 18:269–282 Kokusho T, Yoshida Y (1997) SPT N-value and S-wave velocity for gravelly soils Sharma K, Deng L, Khadka D (2019) Reconnaissance of liquefaction case stud- with different grain size distribution. Soils Found 37(4):105–113. https:// ies in 2015 Gorkha (Nepal) earthquake and assessment of liquefaction doi. org/ 10. 3208/ sandf. 37.4_ 105 susceptibility. Int J Geotech Eng 13:326–338. https:// doi. org/ 10. 1080/ Konagai K, Pokhrel RM, Matsubara H, Shiga M (2015) Geotechnical aspect of 19386 362. 2017. 13503 38 the damage caused by the April 25th. JSCE J Disaster FactSheets Subedi M, Acharya IP (2022) Liquefaction hazard assessment and ground Kyrieleis W, Sichardt W (1930) Grundwasserabsenkung bei fundierungsar- failure probability analysis in the Kathmandu Valley of Nepal. Geoenviron beiten. Julius Springer, Berlin Disasters. https:// doi. org/ 10. 1186/ s40677- 021- 00203-0 Lermo J, Francisco J (1994) Chávez-García; are microtremors useful in site Takai N, Shigefuji M, Rajaure S, Bijukchhen S, Ichiyanagi M, Dhital MR, Sasatani response evaluation. Bull Seismol Soc Am 84(5):1350–1364. https:// doi. T (2016) Strong ground motion in the Kathmandu Valley during the 2015 org/ 10. 1785/ BSSA0 84005 1350 Gorkha, Nepal, earthquake. Earth Planets Sp 68(1):1–8. https:// doi. org/ 10. Maharjan M (2017) Liquefaction in Kathmandu Valley during 2015 Gorkha 1186/ s40623- 016- 0383-7 (Nepal) earthquake. In: 16th World conference on earthquake engineer- Tiwari B, Pradel D, Ajmera B, Yamashiro B, Khadka D (2018) Landslide move- ing 16WCEE 2017 ment at Lokanthali during the 2015 earthquake in Gorkha Nepal. J Geo- McGowan SM, Jaiswal KS, Wald DJ (2017) Using structural damage statistics to tech Geoenviron Eng 144(3):05018001. https:// doi. org/ 10. 1061/ (ASCE) GT. derive macroseismic intensity within the Kathmandu valley for the 2015 1943- 5606. 00018 42 M7. 8 Gorkha, Nepal earthquake. Tectonophys 714-715:158–172. https:// Tokimatsu K, Miyadera Y (1992) Characteristics of Rayleigh waves in micro- doi. org/ 10. 1016/j. tecto. 2016. 08. 002 tremors and their relation to underground structures. J Struct Constr Eng Molnar S, Onwuemeka J, Adhikari S (2017) Rapid post-earthquake micro- 439:81–87 tremor measurements for site amplification and shear wave velocity Tsushima M, Oikawa H (1982) Shear strength and dilatancy of peat. Soils profiling in Kathmandu, Nepal. Earthq Spectra. https:// doi. org/ 10. 1193/ Found 22(2):133–141. https:// doi. org/ 10. 3208/ sandf 1972. 22.2_ 133 12191 6EQS2 45M USGS (2015) M7.8 Nepal Earthquake of 25 April 2015. http:// earth quake. usgs. Moss RE, Thompson EM, Kieffer DS, Tiwari B, Hashash YM, Acharya I, Adhikari gov/ earth quakes/ eqarc hives/ poster/ 2015/ Nepal Summa ry. pdf BR, Asimaki D, Clahan KB, Collins BD (2015) Geotechnical effects of the von Seht MI, Wohlenberg J (1999) Microtremor measurements used to map 2015 magnitude 7.8 Gorkha, Nepal, earthquake and aftershocks. Seismol thickness of soft sediments. Bull Seismol Soc Am 89(1):250–259. https:// Res Lett 86(6):1514–1523. https:// doi. org/ 10. 1785/ 02201 50158doi. org/ 10. 1785/ BSSA0 89001 0250 Nakamura Y (1989) A method for dynamic characteristics estimation of Wang F, Miyajima M, Dahal R (2016) Eec ff ts of topographic and geological subsurface using microtremor on the ground surface. Q Rep Railw Tech features on building damage caused by 2015.4.25 Mw7.8 Gorkha earth- Res Inst 30:25–33 quake in Nepal: a preliminary investigation report. Geoenviron Disasters OCHA (2015) Humanitarian Bulletin Nepal Earthquake Issue 04 (Final Issue). 3:7–7. https:// doi. org/ 10. 1186/ s40677- 016- 0040-2 URL: https://reliefweb.int/report/nepal/humanitarian-bulletin-nepal- Yasuda S, Hashimoto T (2016) New project to prevent liquefaction-induced earthquake-issue-04-final-issue-1-30-september-2015 damage in a wide existing residential area by lowering the ground water Okamura M, Bhandary NP, Mori S, Marasini N, Hazarika H (2015) Report on a table. Soil Dyn Earthq Eng 91:246–259. https:// doi. org/ 10. 1016/j. soild yn. reconnaissance survey of damage in Kathmandu caused by the 2015 2016. 09. 029 Gorkha Nepal earthquake. Soils Found 55(5):1015–1029. https://doi. org/10.1016/j.sandf.2015.09.005 Publisher’s Note Pandey M (2000) Ground response of Kathmandu valley on the basis of micro- Springer Nature remains neutral with regard to jurisdictional claims in pub- tremors. In: Proceedings of the 12th World Conference on Earthquake lished maps and institutional affiliations. Engineering. Parajuli RR, Kiyono J (2015) Ground motion characteristics of the 2015 Gorkha earthquake, survey of damage to stone masonry structures and structural field tests. Front Built Environ. https:// doi. org/ 10. 3389/ fbuil. 2015. 00023 Park C, Miller R, Xia J (1999) Multichannel analysis of surface waves (MASW ). Geophysics. https:// doi. org/ 10. 1190/1. 14445 90 Polito CP, Martin II JR (2001) Eec ff ts of non-plastic fines on the liquefaction resistance of sands. J Geotech Geoenviron Eng 127(5):408–415. https:// doi. org/ 10. 1061/ (ASCE) 1090- 0241(2001) 127: 5(408) Ram TD, Wang G (2011) Probabilistic seismic hazard analysis in Nepal. Earthq Engrg Engrg Vib 12:577–586. https:// doi. org/ 10. 3126/ jiee. v2i1. 36676 Rix GJ, Leipski EA (1991) Accuracy and resolution of surface wave inversion. In: Proceedings of recent advances in instrumentation, data acquisition and testing in soil dynamics Saito M (2006) Fast calculation of the Jacobian of surface wave phase velocity. Butsuri-Tansa/geophys Explor 59(4):381–388. https:// doi. org/ 10. 3124/ segj. 59. 381 Sakai H, Fujii R, Kuwahara Y, Noi H (2000) Climatic changes and tectonic events recorded in the Paleo-Kathmandu lake sediment. J Geogr 109(5):759– 769. https:// doi. org/ 10. 5026/ jgeog raphy. 109. 759 Sakai H, Fujii R, Sugimoto M, Setoguchi R, Paudel MR (2016) Two times lower- ing of lake water at around 48 and 38 ka, caused by possible earthquakes, recorded in the Paleo-Kathmandu lake, central Nepal Himalaya. Earth Planets Sp 68(1):1–10. https:// doi. org/ 10. 1186/ s40623- 016- 0413-5 Shakya M, Kawan CK (2016) Reconnaissance based damage survey of build- ings in Kathmandu valley: an aftermath of 7.8 Mw, April 25th 2015

Journal

Geoenvironmental DisastersSpringer Journals

Published: May 16, 2022

Keywords: 2015 Gorkha earthquake; Kathmandu; Ground fissures; Standard penetration test; Multichannel analysis of surface waves; Spatial ground model

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