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Characteristics of physical properties of the sliding and its surrounding layers in landslides caused by the 2018 Hokkaido Eastern Iburi Earthquake

Characteristics of physical properties of the sliding and its surrounding layers in landslides... A 6.6-M earthquake struck the Iburi region of Hokkaido, Japan, in 2018, triggering massive landslides. Most of these landslides were shallow and occurred mostly in the Atsuma and Abira towns. Ta-c and Ta-d tephra layers have been found in the Towa landslide at Atsuma from the Tarumai volcano, while Ta-d, En-a, and Spfa-1 tephra layers have been found in the Mizuho landslide at Abira from the Tarumai and Eniwa volcanos, as well as the Shikotsu caldera. Field observations from previous studies revealed that the sliding layers were located in the Ta-d and En-a layers at the Towa and Mizuho landslides, respectively. Unlike previous research on earthquake-induced landslides, which were investigated using mechanical properties, this study investigates the characteristics of physical properties, saturated permeability properties, and content of clay minerals on sliding and surrounding tephra layers. Results from this study reveal that the physical properties of sliding layers from two landslides demonstrated the same characteristics: non-plastic soil with a low density of soil particles, void ratio, and dry density; these characteristics could influence earthquake-induced landslides. It also reveals a relationship between the plasticity chart and the age of tephra mate- rials, including the relationship between the weathering process and density of soil particles and the dissimilarity in characteristics of saturated permeability properties in tephra materials. Keywords: Earthquake, Physical properties, Shallow landslide, Sliding layer, Tephra materials Introduction highest in Japan since the Meiji Era (1868–1912) (Osa- A 6.6-M earthquake struck the Iburi region of Hok- nai et  al. 2019). Most landslides were shallow and were kaido, Japan, at 03:08 local time (JST), on September mostly classified as planar and spoon types, both of which 18th, 2018, triggering multiple shallow landslides. The are similar to rainfall-induced landslides. Several deep- maximum earthquake intensity of seven occurred in seated dip-slipping type landslides were also exposed in Atsuma Town, triggering landslides across an area of the south-eastern part of the mountains (Osanai et  al. approximately 20  km behind Atsuma (Yamagishi and 2019; Yamagishi and Yamazaki 2018). The occurrence of Yamazaki 2018). According to an inventory of landslides landslides in Hokkaido is not frequent; similar seismic induced by major earthquakes, the number and total events occurred between 4600 and 2500 years ago (Kasai area of landslides triggered by this earthquake were the and Yamada 2019; Tajika et al. 2016). Furthermore, undis- turbed soil stratigraphy exposed in several landslide scars indicates that these slopes have been stable for more than *Correspondence: goto@yamanashi.ac.jp; goto.satoshi.jp@gmail.com 9000  years (Kasai and Yamada 2019). Kasai and Yamada Faculty of Engineering, Graduate Faculty of Interdisciplinary Research, (2019) also suggested that the combination of low-ele- University of Yamanashi, Kofu, Japan vation relief and tephra layers, which could move very Full list of author information is available at the end of the article © The Author(s) 2022. 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Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 2 of 13 easily in response to ground shaking, might have caused the distribution of tephra layers (Kimura et  al. 2016, unexpectedly large numbers and sizes of landslides when 2019), geomorphological setting (Higaki et  al. 2019), an intense earthquake struck this area. and strength characteristics of gravitational deformation A hypothesis has been presented to explain the numer- (Sato et al. 2017, 2019). Generally, observation of the slid- ous landslides in the Hokkaido Eastern Iburi Earthquake. ing layer on earthquake-induced landslides has been con- The hypothesis suggested that the typhoon on the pre - ducted on mechanical properties, such as observation of vious day could have led to the saturation of pumice monotonic and cyclic behavior in the sliding layer (Goto strata, which absorb large quantities of water. Hence, and Okada 2021). Unlike previous research on earth- this might have triggered a rapid increase in pore pres- quake-induced landslides, which were investigated using sure in the surficial soils during ground shaking, lead - mechanical properties, this study analyzes the physical ing to liquefaction and slope failure (Wang et  al. 2019). properties, saturated permeability properties, and con- However, the hourly intensity of the rainfall brought tent of clay minerals on sliding and surrounding tephra by the typhoon before the earthquake was lower and layers of landslides caused by the 2018 Hokkaido Eastern not enough to trigger a landslide. Zhang et  al. (2019) Iburi Earthquake. The physical properties of soil are also reported persistent rainfall in August, with cumulative observed in the sliding layer in tephra materials on heavy rainfall ranging between 101 and 120  mm, which con- rainfall-induced landslides (Istiyanti et  al. 2020), and tributed significantly to the occurrence of landslides dur - characteristics of tuff breccia-andesite in diverse mecha - ing the intense ground shaking of the Iburi earthquake. nisms of landslides (Istiyanti et al. 2021). They also observed crushed and liquefied pumice layers spread in the deposition area, resulting in the extension Research area of the upper sliding layer in the horizontal direction. The Figure 1 shows the two landslides selected as the research coseismic landslides were highly mobile and had a long- area: one in Atsuma, called the Towa landslide, and runout distance because they were crushed and liquefied another in Abira, called the Mizuho landslide. The dis - on the Ta-d layer (Li et al. 2020; Zhang et al. 2019). tance between the landslides was approximately 12.5 km. The Iburi region has thick tephra deposits from the The basement rocks for these landslides are marine con - eruptions of Mounts Tarumai (approximately 9  ka), glomerates from the Cenozoic, Neogene, Miocene, and Eniwa (approximately 20  ka), and the Shikotsu caldera late Langhian–Tortonian epochs (GSJ 2020); however, (40 ka) (Minato et al. 1972; Nakagawa et al. 2018; Yamag- tephra soils are covered in this area. Osanai et al. (2019) ishi and Yamazaki 2018). Wang et  al. (2019) presents reported that during the Hokkaido Eastern Iburi Earth- an inventory of 7837 coseismic landslides based on the quake, several landslides occurred in the middle reaches interpretation of the images, covering about 24 km of of the Atsuma River in Atsuma and the upper reaches of the disrupted area. Yamagishi and Yamazaki (2018) dis- the Shiabira River in Abira (Fig. 2). covered that tephra layers blanket the region with a depth In Atsuma, the complete tephra layers from Ta-a to of 4–12 m and standard penetration test values were less Spfa-1 were observed (Fig. 3). This observation indicated than 10  N, thus indicating that they are unconsolidated, that some tephra layers were derived from the Tarumai highly compressible, and crushable (Miura 2012). volcano, including Ta-a, b (0.3 ka), Ta-c (2.5 ka), and Ta-d Early observations (Yamagishi and Yamazaki 2018), (8.7–9.2 ka). Other tephra layers erupted from the Eniwa distribution of landslides (Kasai and Yamada 2019; Wang volcano and the Shikotsu caldera. The En-a and Spfa-1 et  al. 2019),  characteristics of landslides (Osanai et  al. layers are tephra layers that erupted from the Eniwa vol- 2019), and clay mineral content (Chigira et  al. 2018; cano (19–21  ka) and Shikotsu caldera (approximately Koyasu et  al. 2020)  have all been studied in this study 40  ka), respectively. Tephra deposits in the Towa land- region (Chigira et al. 2018; Koyasu et al. 2020). The slid - slide were derived from the Tarumai volcano, includ- ing layer of landslides triggered by the Hokkaido Eastern ing Ta-c and Ta-d tephra layers. Generally, Ta-d directly Iburi Earthquake was predominantly formed near the overlies the basement complex on slopes along the main bottoms of layers consisting of volcanic ash and pum- channel of the Atsuma River (Osanai et  al. 2019). Fur- ice from the Tarumai volcano (Ta-d); it was also formed thermore, tephra deposits in the Mizuho landslide were in other tephra layers, such as the En-a layer (Kasai and derived from the Tarumai volcano (Ta-d), Eniwa volcano Yamada 2019; Nakagawa et  al. 2018; Osanai et  al. 2019). (En-a), and Shikotsu caldera (Spfa-1) tephra layers. Furu- Ta-d layers were presumed vulnerable to ground shak- kawa and Nakagawa (2010) and Soya and Sato (1980) ing, which reduces cohesion (Kasai and Yamada 2019). reported that buried humus (kuroboku soil) layers are Studies on heavy rainfall-induced landslides in tephra sandwiched between Ta-b and Ta-c and Ta-c and Ta-d. have also been observed in the prediction of shallow The topsoil layer is generally composed of alternate lay - landslides (Goto and Kimura 2019; Wakai et  al. 2019), ers of pyroclastic fall deposits and buried humus, with a Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 3 of 13 Fig. 1 Location and geological map of research areas (Geology Survey of Japan 2020) thickness of approximately 2.5–3.5 m in the middle of the larger particle size than the Ta-d L layer; Li et al. (2020) slope. This study shows a thin kuroboku layer (0.06 m) as observed that the Ta-d layer decreases top-down. How- the topsoil in the Towa landslide. ever, Tajika et  al. (2016) reported different events in Figure  4 shows the layering of the Towa and Mizuho the Ta-d layer, when the Ta-d U and Ta-d L layers were landslides. The tephra layers from the Tarumai and lithic fragments and pumice fall deposits, respectively. Eniwa volcanos were divided into two sub-layers: upper Similar to the tephra layers from the Towa landslide, (U) and lower (L). In the Towa landslide, the Ta-c layer the Loam (En-a) and En-a layers in the Mizuho land- was divided into Ta-c U and Ta-c L layers because the slide were divided into two parts. Furthermore, differ - Ta-c L layer was located near the weathered Ta-d layer ent particles size was observed in the En-a layer at the and could obtain different characteristics from the Ta-c Mizuho landslide. The En-a U layer had a finer particle U layer. Different particles size was observed in the size than the En-a L layer. Ta-d layer at the Towa landslide. The Ta-d U layer had a Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 4 of 13 Fig. 2 Photo satellite of Atsuma Town (a), Abira Town (b) before and after earthquake, and topographic map on research areas before an earthquake (Geospatial Information Authority of Japan 2020) meter in the exposed soil layer. Furthermore, previous Research methods research observed a discontinuity between the strength This study includes field measurements and laboratory and soil hardness (Tokunaga and Goto 2017). Disturbed tests. For the field measurement, soil stratigraphic was and undisturbed samples were collected from the field; observed, and soil hardness was measured. Soil layers moreover, the undisturbed samples were collected from were exposed by scraping the surface to observe soil the center of each soil layer to observe their saturated stratigraphic, as shown in Fig.  4. The tephra layers in permeability properties in this study. the Towa landslide were scraped in the stage pattern Laboratory tests were conducted to observe the physi- because of the condition of the field. Soil hardness was cal properties, saturated permeability properties, and measured by inserting a Yamanaka-type soil hardness content of clay minerals on tephra materials. The tests for Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 5 of 13 Physical properties of tephra layers The particle size distribution curve (Fig.  6) shows two types of tephra materials: well-graded and poor-graded soil material. Kuroboku, Ta-c L, and Loam (En-a) layers from the Towa landslide, as well as Loam (En-a) U, Loam (En-a) L, and Loam (Spfa-1) layers from the Mizuho landslide contain well-graded soil material. Furthermore, Ta-c U, weathered Ta-d, Ta-d U, and Ta-d L layers from the Towa landslide and weathered Ta-d, En-a U, and En-a L layers from the Mizuho landslide are tephra materials with poor-graded soil material. Tephra layers trigger complex and peculiar geotechni- cal engineering challenges in all regions (Miura 2012), and poor-graded soils are more susceptible to soil lique- faction than well-graded soils (Holtz and Kovacs 1981). Fig. 3 The tephra layers from Ta-a until Spfa-1 which located nearby Moreover, pumice grains in tephra have many open voids the research area (Minato et al. 1972; Nakagawa et al. 2018; Yamagishi within a single grain, and when they are sheared, these and Yamazaki 2018) (Photos taken on September 2019) voids are initially closed with the fracturing of void walls, then grain fragments float in squeezed water (Chigira and Suzuki 2016). Therefore, because the sliding layers the physical properties were conducted according to the (Ta-d L and En-a) with poor-graded soil material have laboratory testing standards of Geomaterials Vol. 1 (JGS many open voids, these layers easily collapse during the 2015). Additionally, a particle size distribution test on earthquake. the tephra layer was performed by sieve and sedimenta- The physical properties of the tephra layers in the Towa tion analyses on all tephra layers, except the weathered and Mizuho landslides (Fig. 5a, b) indicated a dissimilar- Ta-d and En-a L layers from the Mizuho landslide. Sieve ity between sliding layers. The density of soil particles on analysis in this study only observed these layers. The test tephra layers in the Towa and Mizuho landslides indi- for the saturated permeability properties was performed cated that the sliding layers show a low density of soil according to the methods for obtaining the saturated per- particles. Arthurs (2010) reported that the low density of meability of soils presented by Daiki (DIK-4012). Clay soil particles on tephra layers made it easier for materi- minerals on tephra layers were also observed using X-ray als to move in landslides, which tended to create longer diffraction (XRD) tests which were performed according runout distances than similar landslides in denser soils. to the randomly oriented powder mounts, ethylene glycol This study observed the low density of soil particles on treatment, and heat treatment methods from the United weathered Ta-d in the Towa and Mizuho landslides. States Geological Survey (USGS). The weathering process in the weathered Ta-d layer was rapid, allowing the density of soil particle value to decrease. Therefore, the density of soil particles could Results and discussion be related to the sliding layer and weathering process in Field observations tephra materials. The sliding layers from field observation were located in The physical properties of the tephra layers (Fig.  5a, b) the Ta-d and En-a layers at the Towa and Mizuho land- indicated that the plasticity index of the sliding layer in slides, respectively. Figure  5a, b show the soil hardness the Towa and Mizuho landslides is non-plastic soil. The measurements during field observations. The soil hard - non-plastic sliding layer showed that the sliding layer is ness in the Towa landslide indicates that the Ta-c U layer stiff soil, which could influence earthquake-induced land - has the lowest average value of soil hardness, whereas the slides. The liquid and plastic limit test results are also Ta-d U layer has the highest average value of soil hard- used in the plasticity chart, which classifies the soil mate - ness. Additionally, the soil hardness in the Mizuho land- rials (Fig.  7), denoted by different colors, while sliding slide shows that the Loam (Spfa-1) layer has the lowest layers on each area are denoted by white circles with dif- average value of soil hardness, whereas the weathered ferent colored outlines. The plotted data on the plasticity En-a layer has the highest average value of soil hardness. chart compares the tephra materials from landslides with However, there was no significant difference in the soil tephra materials from Aso volcanic mountain (Istiyanti hardness of the sliding layer of both landslides. et al. 2020). Istiyanti et al. (2020) revealed that kuroboku and scoria have different characteristics, whereas the Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 6 of 13 Fig. 4 Plan section and cross section on research areas; a Towa landslide, b Mizuho landslide (Geospatial Information Authority of Japan 2020) Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 7 of 13 Fig. 5 Soil stratigraphy on the field, soil hardness, physical properties, and saturated permeability properties values in research area with dotted lines indicate sliding layer by field observation; a Towa landslide, b Mizuho landslide sliding layers (N3-4 kuroboku (L) layers) have the high- while those of earthquake-induced landslides on tephra est plasticity index and liquid limit values and are plotted at Hokkaido have non-plastic soil. in the kuroboku group on the plasticity chart. Therefore, Furthermore, the plasticity chart divided the tephra the sliding layers of heavy rainfall-induced landslides on materials from the Towa and Mizuho landslides into tephra at Aso volcanic mountains have high plasticity, three types: inorganic silts of medium compressibility and organic silts, inorganic silts of high compressibility Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 8 of 13 Fig. 6 Particle size distribution curves of tephra materials organic clays, and non-plastic (NP). The kuroboku the older tephra materials probably have higher liquid and Ta-c L layers from the Towa landslide, including limit and plasticity index values, if the tephra materials the Loam (En-a) U and Loam (En-a) L layers from the are very old, they probably do not have plasticity values, Mizuho landslide, are inorganic silts of medium com- i.e., they belong to the NP soil. Unfortunately, a different pressibility and organic silts with lower liquid limit and result was obtained for the Ta-c U layer, which belongs plasticity index values. Furthermore, weathered Ta-d, to the NP soil, although the Ta-c U layer was not an old Ta-d U, and Loam (En-a) layers from the Towa landslide tephra material. and weathered Ta-d layer from the Mizuho landslide are inorganic silts of high compressibility and organic clays Saturated permeability properties with higher liquid limit and plasticity index values. The Figure  5a, b show the saturated permeability properties NP group consists of Ta-c U and Ta-d L layers from the of the tephra materials. This study measured the satu - Towa landslide and En-a U, En-a L, and Loam (Spfa-1) rated permeability properties of each tephra layer from layers from the Mizuho landslide. the Towa landslide and on the En-a U, En-a L, and Loam The plotted data on the plasticity chart also shows three (Spfa-1) layers from the Mizuho landslide. A significant groups of tephra materials: scoria (N2 scoria: 1.5  ka and peculiarity was observed in the Ta-d U layer of the Towa OJS scoria: 3.6 ka), kuroboku, and Ta-d (8.7–9.2 ka); the landslide. The Ta-d U layer exhibited the highest water chart is possibly related to the age of the tephra materials. content, coefficient of saturated permeability, and void The scoria group with the youngest age has lower liquid ratio with the lowest dry density value. The different limit and plasticity index values than the Ta-d group. The characteristics of saturated permeability in the Ta-d U Ta-c L layer (2.5 ka) was also included in the scoria group layer could be related to the different events in the Ta-d because it is almost similar to the scoria. Moreover, the layer. Different characteristics of saturated permeability oldest tephra material, the En-a layer, was NP. This study were also observed between the sliding and the under assumed that young tephra materials probably have layers. The dissimilarity in the void ratio and dry density lower liquid limit and plasticity index values; although indicated that the sliding layers have a loose structure. Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 9 of 13 Fig. 7 Ellipse pattern from plotted data of tephra materials in Aso volcanic mountains (Istiyanti et al. 2020) and plotted data of tephra materials from Hokkaido on plasticity chart Although the pore water pressure did not affect the land - Characteristics of soil physical properties on the sliding slides, the loose structure on the sliding layers could have layer influenced the landslides. During the earthquake, sliding The sliding layer on earthquake-induced landslides is a layers with loose structures easily collapse. Chang et  al. NP soil with a low density of soil particles, void ratio, and (2020) reported that loose materials accumulated on the dry density. The physical properties of the sliding layer slopes are more likely to fail during an earthquake. showed that the sliding layer is a stiff soil with a loose Furthermore, the relationship between the void ratio structure. Furthermore, the sliding layer on earthquake- and the coefficient of saturated permeability (Fig.  8) indi- induced landslides has a halloysite, which could have cated the dissimilarity in tephra layers. Although Ta-d affected the layer during the earthquake. This is because layers from the Towa landslide have several void ratios, the presence of the halloysite indicates that it is poten- the Ta-c, En-a, and Loam layers have a narrow range of tially weak, which explains the appearance of shrinkage void ratios. The Ta-d U and En-a layers from the Towa cracks (Moon et al. 2015). and Mizuho landslides have a considerable coefficient of Therefore, the characteristics of the sliding layer on saturated permeability, respectively. Shimizu and Ono tephra materials in earthquake-induced landslides are (2016) determined the saturated permeability proper- stiff soil with a loose structure, and the halloysite con - ties of tephra layers from the Aso volcanic mountain area tent in the sliding layer triggers shrinkage and cracks and reported that the hydraulic conductivity at the layer in the layer. During the earthquake, the loose structure below the sliding layer in heavy rainfall-induced land- and cracks on the sliding layer could not handle the driv- slides was decreased, and the difference in hydraulic con - ing force, i.e., the mass of the upper layers, causing the ductivity affects the tephra layer. Because the landslides landslide. in this study were triggered by an earthquake, no differ - ences in hydraulic conductivity were found between the sliding and under layers. Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 10 of 13 Fig. 8 Correlation between coefficient of permeability (m/s) and void ratio Content of clay minerals and halloysite (kaolinite group). Furthermore, the En-a The USGS  (2001) classified clay minerals into seven layer contains illite, chlorite, montmorillonite (smectite groups in its laboratory manual for XRD:chlorite, illite, group), and kaolinite group (dickite and halloysite). kaolinite, mixed-layer clays, smectite, sepiolite, palygor- There was no significant difference in the content of skite, and vermiculite. The clay minerals in the tephra lay - clay minerals in the tephra layers of the Mizuho land- ers from the Towa landslide generally contained smectite slide. Additionally, the Ta-d L layer from the Towa land- clay minerals (Fig.  9a). Kuroboku layers contain chlorite, slide contained a halloysite, whereas other tephra layers illite–smectite, and montmorillonite (smectite group). in the Towa landslide did not. Chigira et  al. (2018) and Furthermore, the Ta-c U, Ta-c L, and Loam (En-a) layers Koyasu et al. (2020) confirmed the presence of halloysite contain montmorillonite (smectite group). The weath - in tephra layers. Chigira et  al. (2018) confirmed that the ered Ta-d layer contains chlorite and montmorillonite sliding layer is at the Ta-d layer, which has a halloysite, (smectite group), and the Ta-d L layer contains halloysite and that a large amount of water is contained within the (kaolinite group) and montmorillonite (smectite group). halloysite formation. Surprisingly, this peak was not observed in the Ta-d U layer. Conclusion The clay minerals in the tephra layers from the Miz - According to previous studies, the physical properties uho landslide generally contained smectite and kaolinite of sliding layers from two landslides revealed the same clay minerals (Fig.  9b). The weathered Ta-d layer con - characteristics, NP soil with low density of soil parti- tains illite, chlorite, smectite group (montmorillonite and cles, void ratio, and dry density, and these characteristics smectite), and kaolinite group (dickite and halloysite). could influence earthquake-induced landslides. Further - The Loam (En-a) U layer contains illite, chlorite, mont - more, the sliding layer contains halloysite, which could morillonite (smectite group), and halloysite (kaolinite have caused cracks. This study revealed that the charac - group). The Loam (En-a) L layer contains illite, chlorite, teristics of physical properties influence the sliding layer. illite-montmorillonite, montmorillonite (smectite group), During the earthquake, the loose structure and cracks in Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 11 of 13 Fig. 9 Clay minerals on tephra materials from Towa and Mizuho landslides Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 12 of 13 Received: 31 January 2022 Accepted: 30 September 2022 the sliding layer could not handle the driving force, which is the mass of the upper layers, thereby triggering the landslide. The physical and saturated permeability properties References of the Towa landslide also indicated different charac - Arthurs JM (2010) The nature of sensitivity in rhyolitic pyroclastic soils from teristics of the Ta-d U layer. This phenomenon could be New Zealand. Dissertation, University of Auckland Chang M, Zhou Y, Zhou C, Hales TC (2020) Coseismic landslide induced by because the different events that formed the particle size the 2018 M 6.6 Iburi, Japan, Earthquake: spatial distribution, key factors on the Ta-d U layer were more significant than those of weight, and susceptibility regionalization. Landslides. https:// doi. org/ 10. the other tephra layers. Additionally, there is a possible 1007/ s10346- 020- 01522-3 Chigira M, Suzuki T (2016) Prediction of earthquake-induced landslides of relationship between the age of the tephra materials and pyroclastic fall deposits. In: Aversa S et al (eds) Landslides and engineered the plasticity index. Young tephra materials have lower slopes. Experience, theory, and practice. Associazione Geotecnica Italiana, liquid limit and plasticity index values than older tephra Rome, pp 93–100 Chigira M, Tajika J, Ishimaru S (2018) Formation beds of sliding surface-weath- materials. Furthermore, if the tephra materials are very ering and clay minerals. Hokkaido University Press, Sapporo (in Japanese old, they are probably included in the NP soil. The dis - with English abstract) similarity between the characteristics of the saturated Daiki (DIK-4012) (n.d) Manual for soil permeability analysis using an instrument with four points (in Japanese) permeability properties was also observed in the tephra Furukawa R, Nakagawa M (2010) Geological map of Tarumae volcano. https:// layers. This study also indicates the relationship between gbank. gsj. jp/ volca no/ Act_ Vol/ tarum ae/ index-e. html. Accessed Oct 2020 the weathering process and the density of soil particles. Geology Survey of Japan. https:// gbank. gsj. jp/ geona vi/ geona vi. php. Accessed Oct 2020 Unfortunately, there was no significant difference in the Geospatial Information Authority of Japan. https:// maps. gsi. go. jp/. Accessed sliding layer of tephra materials at earthquake-induced Oct 2020 landslides in terms of soil hardness value and clay min- Goto S, Kimura T (2019) Introduction of the special issue on “Toward the prediction of shallow landslides induced by heavy rainfalls on tephra- eral content. covered slopes.” J Jpn Landslide Soc 56:211–217. https:// doi. org/ 10. 3313/ jls. 56. 211 (in Japanese) Acknowledgements Goto S, Okada K (2021) Monotonic and cyclic behaviour of tephra layer The field observations in this study were made possible with the participation landslide at Takanodai from the 2016 Kumamoto earthquake. In: Tiwari of Geotechnical Laboratory members from the University of Yamanashi. B, Sassa K, Bobrowsky PT, Takara K (eds) Understanding and reducing landslide disaster risk. WLF 2020. ICL contribution to landslide disaster risk Author contributions reduction. Springer, Cham. https:// doi. org/ 10. 1007/ 978-3- 030- 60706-7_ MLI and SG visited the landslide sites and selected a location to expose the soil materials, collected samples, and conducted a field investigation to Higaki D, Li X, Hayashi I, Tsou C, Kimura T, Hayashi S, Sato G, Goto S (2019) measure soil hardness. MLI performed physical properties, saturated perme- Geomorphological setting of shallow landslides by heavy rainfall on ability, and XRD tests. MLI and SG analyzed and interpreted the soil behavior tephra-covered slopes of Aso volcano, southwest Japan. J Jpn Landslide regarding the materials at the landslide sites. Both authors read and approved Soc 56:218–226. https:// doi. org/ 10. 3313/ jls. 56. 218 (in Japanese with the final manuscript. English abstract) Holtz RD, Kovacs WD (1981) An introduction to geotechnical engineering. Funding Prentice Hall, Englewood Cliffs Part of this study was carried out with the support of the Japan Society for the Istiyanti ML, Goto S, Kimura T, Sato G, Hayashi S, Wakai A, Higaki D (2020) Promotion of Science Grants-in-Aid for Scientific Research (B) 17H03303 for Sliding layer estimation of shallow landslides on Aso volcanic mountains 2017-2019. in Japan based on tephra layer-physical properties of soil. Geoenviron Disasters 7:28. https:// doi. org/ 10. 1186/ s40677- 020- 00163-x Availability of data and materials Istiyanti ML, Goto S, Ochiai H (2021) Characteristics of tuff breccia-andesite The datasets used and/or analyzed during the study were obtained from the in diverse mechanisms of landslides in Oita Prefecture, Kyushu, Japan. corresponding author upon request. Geoenviron Disasters. https:// doi. org/ 10. 1186/ s40677- 021- 00176-0 Kasai M, Yamada T (2019) Topographic effects on the frequency-size Declarations distribution of landslides triggered by the Hokkaido Eastern Iburi Earthquake in 2018. Earth Planets Space 71:89. https:// doi. org/ 10. 1186/ Ethics approval and consent to participate s40623- 019- 1069-8 Not applicable. Kimura T, Goto S, Sato G, Wakai A, Doshida S (2016) Thickness distribution of pyroclastic fall layers on outer slopes of the caldera rim, Izu Oshima Consent for publication Volcano. J Jpn Landslide Soc 53(2):43–49. https:// doi. org/ 10. 3313/ jls. 53. 43 Submission of an article implies that the work described has not been pub- (in Japanese with English abstract) lished previously, that it is not under consideration for publication elsewhere. Kimura T, Goto S, Sato G, Wakai A, Hayashi S, Higaki D (2019) Evaluation of The publication is approved by all authors and tacitly or explicitly by the landslide susceptibility by slope stability analysis using an estimated responsible authorities where the work was carried out. If accepted, it will not distribution of tephra deposits—a case study in the northeastern part of be published elsewhere in the same form, in English, or any other language, Aso caldera. J Jpn Landslide Soc 56:240–249. https:// doi. org/ 10. 3313/ jls. including electronically without the written consent of the copyright holder. 56. 240 (in Japanese with English abstract) Koyasu H, Ishimaru S, Wang G, Furuya G, Watanabe N, Cai F, Uchimura T, Kimura Competing interests T (2020) Geological and geotechnical characteristics of sliding layers of The authors declare that they have no competing interests. landslides introduced by the 2018 Hokkaido Eastern Iburi earthquake. http:// www. dpri. kyoto-u. ac. jp/ hapyo/ 20/ pdf/ D32. pdf. Accessed Nov Author details 1 2 Bandung, West Java, Indonesia. Faculty of Engineering, Graduate Faculty of Interdisciplinary Research, University of Yamanashi, Kofu, Japan. Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 13 of 13 Li R, Wang F, Zhang S (2020) Controlling role of Ta-d pumice on the coseismic Publisher’s Note landslides triggered by 2018 Hokkaido Eastern Iburi Earthquake. 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In: Volcanic rocks and soils—proceedings of the international workshop on volcanic rocks and soils, pp 3–21. https:// doi. org/ 10. 1201/ b18897-1 Nakagawa M, Amma-Miyasaka M, Tomijima C, Matsumoto A, Hase R (2018) Eruption sequence of the 46 ka caldera-forming eruption of Shikotsu Volcano, inferred from stratigraphy of proximal deposits at South of Lake Shikotsu, Japan. J Geogr 127(2):247–271. https:// doi. org/ 10. 5026/ jgeog raphy. 127. 247 (in Japanese with English abstract) Osanai N, Yamada T, Hayashi S, Kastura S, Furuichi T, Yanai S, Murakami Y, Miyazaki T, Tanioka Y, Takiguchi S, Miyazaki M (2019) Characteristics of landslides caused by the 2018 Hokkaido Eastern Iburi Earthquake. Land- slides 16:1517–1528. https:// doi. org/ 10. 1007/ s10346- 019- 01206-7 Sato G, Goto S, Kimura T, Hayashi S, Istiyanti ML, Komori J (2017) Gravitational deformation as a precursor of the shallow landslide within tephra- covered slope deposits in the Aso caldera, Japan. J Jpn Landslide Soc 54(5):199–204. https:// doi. org/ 10. 3313/ jls. 54. 199 (in Japanese with English abstract) Sato G, Wakai A, Goto S, Kimura T (2019) Strength characteristics of gravitation- ally deformed slope deposits of tephra and kuroboku soils in the Aso cal- dera, Japan—application of revised vane-shear-cone test for estimating shear strength. J Jpn Landslide Soc 56:250–253. https:// doi. org/ 10. 3313/ jls. 56. 250 (in Japanese with English abstract) Shimizu O, Ono M (2016) Relationship of tephra stratigraphy and hydraulic conductivity with slide depth in rainfall-induced shallow landslides in Aso Volcano. Jpn Landslides 13(3):577–582. https:// doi. org/ 10. 1007/ s10346- 015- 0666-2 Soya T, Sato H (1980) Geology of the Chitose District Quadrangle Series 1: 50,000. Geol. Surv. Japan, pp 92 Tajika J, Ohtsu S, Inui T (2016) Interior structure and sliding process of landslide body composed of stratified pyroclastic fall deposits at the Apporo 1 archaeological site, southeastern margin of the Ishikari Lowland, Hok- kaido, North Japan. J Geol Soc Jpn 122(1):23–35 (in Japanese with English abstract) The Japanese Geotechnical Society (2015) Japanese Geotechnical Society Standards-Laboratory testing standards of geomaterials, vol 1 Tokunaga S, Goto S (2017) Study on measurement of strength discontinuity by digitized Yamanaka soil hardness tester for shallow landslide site at Aso volcano. 52nd Japan Society for Geotechnical Nagoya, July 2017, pp 1935–1936 (in Japanese) US Geological Survey (2001) A laboratory manual for X-ray powder diffraction. https:// pubs. usgs. gov/ of/ 2001/ of01- 041/ index. htm. Accessed July 2020 Wakai A, Hori K, Watanabe A, Cai F, Fukazu H, Goto S, Kimura T (2019) A simple prediction model for shallow groundwater level rise in natural slopes based on finite element solutions. J Jpn Landslide Soc 56:227–239. https:// doi. org/ 10. 3313/ jls. 56. 227 (in Japanese with English abstract) Wang F, Fan X, Yunus AP, Subramanian SS, Alonso-Rodriguez A, Dai L, Xu Q, Huang R (2019) Coseismic landslides triggered by the 2018 Hokkaido, Japan (M 6.6), earthquake: spatial distribution, controlling factors, and possible failure mechanism. Landslides 16:1551–1566. https:// doi. org/ 10. 1007/ s10346- 019- 01187-7 Yamagishi H, Yamazaki F (2018) Landslides by the 2018 Hokkaido Iburi-Tobu Earthquake on September 6. Landslides 15:2521–2524. https:// doi. org/ 10. 1007/ s10346- 018- 1092-z Zhang S, Li R, Wang F, Iio A (2019) Characteristics of landslides triggered by the 2018 Hokkaido Eastern Iburi earthquake, Northern Japan. Landslides 16:1691–1708. https:// doi. org/ 10. 1007/ s10346- 019- 01207-6 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Characteristics of physical properties of the sliding and its surrounding layers in landslides caused by the 2018 Hokkaido Eastern Iburi Earthquake

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Abstract

A 6.6-M earthquake struck the Iburi region of Hokkaido, Japan, in 2018, triggering massive landslides. Most of these landslides were shallow and occurred mostly in the Atsuma and Abira towns. Ta-c and Ta-d tephra layers have been found in the Towa landslide at Atsuma from the Tarumai volcano, while Ta-d, En-a, and Spfa-1 tephra layers have been found in the Mizuho landslide at Abira from the Tarumai and Eniwa volcanos, as well as the Shikotsu caldera. Field observations from previous studies revealed that the sliding layers were located in the Ta-d and En-a layers at the Towa and Mizuho landslides, respectively. Unlike previous research on earthquake-induced landslides, which were investigated using mechanical properties, this study investigates the characteristics of physical properties, saturated permeability properties, and content of clay minerals on sliding and surrounding tephra layers. Results from this study reveal that the physical properties of sliding layers from two landslides demonstrated the same characteristics: non-plastic soil with a low density of soil particles, void ratio, and dry density; these characteristics could influence earthquake-induced landslides. It also reveals a relationship between the plasticity chart and the age of tephra mate- rials, including the relationship between the weathering process and density of soil particles and the dissimilarity in characteristics of saturated permeability properties in tephra materials. Keywords: Earthquake, Physical properties, Shallow landslide, Sliding layer, Tephra materials Introduction highest in Japan since the Meiji Era (1868–1912) (Osa- A 6.6-M earthquake struck the Iburi region of Hok- nai et  al. 2019). Most landslides were shallow and were kaido, Japan, at 03:08 local time (JST), on September mostly classified as planar and spoon types, both of which 18th, 2018, triggering multiple shallow landslides. The are similar to rainfall-induced landslides. Several deep- maximum earthquake intensity of seven occurred in seated dip-slipping type landslides were also exposed in Atsuma Town, triggering landslides across an area of the south-eastern part of the mountains (Osanai et  al. approximately 20  km behind Atsuma (Yamagishi and 2019; Yamagishi and Yamazaki 2018). The occurrence of Yamazaki 2018). According to an inventory of landslides landslides in Hokkaido is not frequent; similar seismic induced by major earthquakes, the number and total events occurred between 4600 and 2500 years ago (Kasai area of landslides triggered by this earthquake were the and Yamada 2019; Tajika et al. 2016). Furthermore, undis- turbed soil stratigraphy exposed in several landslide scars indicates that these slopes have been stable for more than *Correspondence: goto@yamanashi.ac.jp; goto.satoshi.jp@gmail.com 9000  years (Kasai and Yamada 2019). Kasai and Yamada Faculty of Engineering, Graduate Faculty of Interdisciplinary Research, (2019) also suggested that the combination of low-ele- University of Yamanashi, Kofu, Japan vation relief and tephra layers, which could move very 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/. Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 2 of 13 easily in response to ground shaking, might have caused the distribution of tephra layers (Kimura et  al. 2016, unexpectedly large numbers and sizes of landslides when 2019), geomorphological setting (Higaki et  al. 2019), an intense earthquake struck this area. and strength characteristics of gravitational deformation A hypothesis has been presented to explain the numer- (Sato et al. 2017, 2019). Generally, observation of the slid- ous landslides in the Hokkaido Eastern Iburi Earthquake. ing layer on earthquake-induced landslides has been con- The hypothesis suggested that the typhoon on the pre - ducted on mechanical properties, such as observation of vious day could have led to the saturation of pumice monotonic and cyclic behavior in the sliding layer (Goto strata, which absorb large quantities of water. Hence, and Okada 2021). Unlike previous research on earth- this might have triggered a rapid increase in pore pres- quake-induced landslides, which were investigated using sure in the surficial soils during ground shaking, lead - mechanical properties, this study analyzes the physical ing to liquefaction and slope failure (Wang et  al. 2019). properties, saturated permeability properties, and con- However, the hourly intensity of the rainfall brought tent of clay minerals on sliding and surrounding tephra by the typhoon before the earthquake was lower and layers of landslides caused by the 2018 Hokkaido Eastern not enough to trigger a landslide. Zhang et  al. (2019) Iburi Earthquake. The physical properties of soil are also reported persistent rainfall in August, with cumulative observed in the sliding layer in tephra materials on heavy rainfall ranging between 101 and 120  mm, which con- rainfall-induced landslides (Istiyanti et  al. 2020), and tributed significantly to the occurrence of landslides dur - characteristics of tuff breccia-andesite in diverse mecha - ing the intense ground shaking of the Iburi earthquake. nisms of landslides (Istiyanti et al. 2021). They also observed crushed and liquefied pumice layers spread in the deposition area, resulting in the extension Research area of the upper sliding layer in the horizontal direction. The Figure 1 shows the two landslides selected as the research coseismic landslides were highly mobile and had a long- area: one in Atsuma, called the Towa landslide, and runout distance because they were crushed and liquefied another in Abira, called the Mizuho landslide. The dis - on the Ta-d layer (Li et al. 2020; Zhang et al. 2019). tance between the landslides was approximately 12.5 km. The Iburi region has thick tephra deposits from the The basement rocks for these landslides are marine con - eruptions of Mounts Tarumai (approximately 9  ka), glomerates from the Cenozoic, Neogene, Miocene, and Eniwa (approximately 20  ka), and the Shikotsu caldera late Langhian–Tortonian epochs (GSJ 2020); however, (40 ka) (Minato et al. 1972; Nakagawa et al. 2018; Yamag- tephra soils are covered in this area. Osanai et al. (2019) ishi and Yamazaki 2018). Wang et  al. (2019) presents reported that during the Hokkaido Eastern Iburi Earth- an inventory of 7837 coseismic landslides based on the quake, several landslides occurred in the middle reaches interpretation of the images, covering about 24 km of of the Atsuma River in Atsuma and the upper reaches of the disrupted area. Yamagishi and Yamazaki (2018) dis- the Shiabira River in Abira (Fig. 2). covered that tephra layers blanket the region with a depth In Atsuma, the complete tephra layers from Ta-a to of 4–12 m and standard penetration test values were less Spfa-1 were observed (Fig. 3). This observation indicated than 10  N, thus indicating that they are unconsolidated, that some tephra layers were derived from the Tarumai highly compressible, and crushable (Miura 2012). volcano, including Ta-a, b (0.3 ka), Ta-c (2.5 ka), and Ta-d Early observations (Yamagishi and Yamazaki 2018), (8.7–9.2 ka). Other tephra layers erupted from the Eniwa distribution of landslides (Kasai and Yamada 2019; Wang volcano and the Shikotsu caldera. The En-a and Spfa-1 et  al. 2019),  characteristics of landslides (Osanai et  al. layers are tephra layers that erupted from the Eniwa vol- 2019), and clay mineral content (Chigira et  al. 2018; cano (19–21  ka) and Shikotsu caldera (approximately Koyasu et  al. 2020)  have all been studied in this study 40  ka), respectively. Tephra deposits in the Towa land- region (Chigira et al. 2018; Koyasu et al. 2020). The slid - slide were derived from the Tarumai volcano, includ- ing layer of landslides triggered by the Hokkaido Eastern ing Ta-c and Ta-d tephra layers. Generally, Ta-d directly Iburi Earthquake was predominantly formed near the overlies the basement complex on slopes along the main bottoms of layers consisting of volcanic ash and pum- channel of the Atsuma River (Osanai et  al. 2019). Fur- ice from the Tarumai volcano (Ta-d); it was also formed thermore, tephra deposits in the Mizuho landslide were in other tephra layers, such as the En-a layer (Kasai and derived from the Tarumai volcano (Ta-d), Eniwa volcano Yamada 2019; Nakagawa et  al. 2018; Osanai et  al. 2019). (En-a), and Shikotsu caldera (Spfa-1) tephra layers. Furu- Ta-d layers were presumed vulnerable to ground shak- kawa and Nakagawa (2010) and Soya and Sato (1980) ing, which reduces cohesion (Kasai and Yamada 2019). reported that buried humus (kuroboku soil) layers are Studies on heavy rainfall-induced landslides in tephra sandwiched between Ta-b and Ta-c and Ta-c and Ta-d. have also been observed in the prediction of shallow The topsoil layer is generally composed of alternate lay - landslides (Goto and Kimura 2019; Wakai et  al. 2019), ers of pyroclastic fall deposits and buried humus, with a Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 3 of 13 Fig. 1 Location and geological map of research areas (Geology Survey of Japan 2020) thickness of approximately 2.5–3.5 m in the middle of the larger particle size than the Ta-d L layer; Li et al. (2020) slope. This study shows a thin kuroboku layer (0.06 m) as observed that the Ta-d layer decreases top-down. How- the topsoil in the Towa landslide. ever, Tajika et  al. (2016) reported different events in Figure  4 shows the layering of the Towa and Mizuho the Ta-d layer, when the Ta-d U and Ta-d L layers were landslides. The tephra layers from the Tarumai and lithic fragments and pumice fall deposits, respectively. Eniwa volcanos were divided into two sub-layers: upper Similar to the tephra layers from the Towa landslide, (U) and lower (L). In the Towa landslide, the Ta-c layer the Loam (En-a) and En-a layers in the Mizuho land- was divided into Ta-c U and Ta-c L layers because the slide were divided into two parts. Furthermore, differ - Ta-c L layer was located near the weathered Ta-d layer ent particles size was observed in the En-a layer at the and could obtain different characteristics from the Ta-c Mizuho landslide. The En-a U layer had a finer particle U layer. Different particles size was observed in the size than the En-a L layer. Ta-d layer at the Towa landslide. The Ta-d U layer had a Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 4 of 13 Fig. 2 Photo satellite of Atsuma Town (a), Abira Town (b) before and after earthquake, and topographic map on research areas before an earthquake (Geospatial Information Authority of Japan 2020) meter in the exposed soil layer. Furthermore, previous Research methods research observed a discontinuity between the strength This study includes field measurements and laboratory and soil hardness (Tokunaga and Goto 2017). Disturbed tests. For the field measurement, soil stratigraphic was and undisturbed samples were collected from the field; observed, and soil hardness was measured. Soil layers moreover, the undisturbed samples were collected from were exposed by scraping the surface to observe soil the center of each soil layer to observe their saturated stratigraphic, as shown in Fig.  4. The tephra layers in permeability properties in this study. the Towa landslide were scraped in the stage pattern Laboratory tests were conducted to observe the physi- because of the condition of the field. Soil hardness was cal properties, saturated permeability properties, and measured by inserting a Yamanaka-type soil hardness content of clay minerals on tephra materials. The tests for Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 5 of 13 Physical properties of tephra layers The particle size distribution curve (Fig.  6) shows two types of tephra materials: well-graded and poor-graded soil material. Kuroboku, Ta-c L, and Loam (En-a) layers from the Towa landslide, as well as Loam (En-a) U, Loam (En-a) L, and Loam (Spfa-1) layers from the Mizuho landslide contain well-graded soil material. Furthermore, Ta-c U, weathered Ta-d, Ta-d U, and Ta-d L layers from the Towa landslide and weathered Ta-d, En-a U, and En-a L layers from the Mizuho landslide are tephra materials with poor-graded soil material. Tephra layers trigger complex and peculiar geotechni- cal engineering challenges in all regions (Miura 2012), and poor-graded soils are more susceptible to soil lique- faction than well-graded soils (Holtz and Kovacs 1981). Fig. 3 The tephra layers from Ta-a until Spfa-1 which located nearby Moreover, pumice grains in tephra have many open voids the research area (Minato et al. 1972; Nakagawa et al. 2018; Yamagishi within a single grain, and when they are sheared, these and Yamazaki 2018) (Photos taken on September 2019) voids are initially closed with the fracturing of void walls, then grain fragments float in squeezed water (Chigira and Suzuki 2016). Therefore, because the sliding layers the physical properties were conducted according to the (Ta-d L and En-a) with poor-graded soil material have laboratory testing standards of Geomaterials Vol. 1 (JGS many open voids, these layers easily collapse during the 2015). Additionally, a particle size distribution test on earthquake. the tephra layer was performed by sieve and sedimenta- The physical properties of the tephra layers in the Towa tion analyses on all tephra layers, except the weathered and Mizuho landslides (Fig. 5a, b) indicated a dissimilar- Ta-d and En-a L layers from the Mizuho landslide. Sieve ity between sliding layers. The density of soil particles on analysis in this study only observed these layers. The test tephra layers in the Towa and Mizuho landslides indi- for the saturated permeability properties was performed cated that the sliding layers show a low density of soil according to the methods for obtaining the saturated per- particles. Arthurs (2010) reported that the low density of meability of soils presented by Daiki (DIK-4012). Clay soil particles on tephra layers made it easier for materi- minerals on tephra layers were also observed using X-ray als to move in landslides, which tended to create longer diffraction (XRD) tests which were performed according runout distances than similar landslides in denser soils. to the randomly oriented powder mounts, ethylene glycol This study observed the low density of soil particles on treatment, and heat treatment methods from the United weathered Ta-d in the Towa and Mizuho landslides. States Geological Survey (USGS). The weathering process in the weathered Ta-d layer was rapid, allowing the density of soil particle value to decrease. Therefore, the density of soil particles could Results and discussion be related to the sliding layer and weathering process in Field observations tephra materials. The sliding layers from field observation were located in The physical properties of the tephra layers (Fig.  5a, b) the Ta-d and En-a layers at the Towa and Mizuho land- indicated that the plasticity index of the sliding layer in slides, respectively. Figure  5a, b show the soil hardness the Towa and Mizuho landslides is non-plastic soil. The measurements during field observations. The soil hard - non-plastic sliding layer showed that the sliding layer is ness in the Towa landslide indicates that the Ta-c U layer stiff soil, which could influence earthquake-induced land - has the lowest average value of soil hardness, whereas the slides. The liquid and plastic limit test results are also Ta-d U layer has the highest average value of soil hard- used in the plasticity chart, which classifies the soil mate - ness. Additionally, the soil hardness in the Mizuho land- rials (Fig.  7), denoted by different colors, while sliding slide shows that the Loam (Spfa-1) layer has the lowest layers on each area are denoted by white circles with dif- average value of soil hardness, whereas the weathered ferent colored outlines. The plotted data on the plasticity En-a layer has the highest average value of soil hardness. chart compares the tephra materials from landslides with However, there was no significant difference in the soil tephra materials from Aso volcanic mountain (Istiyanti hardness of the sliding layer of both landslides. et al. 2020). Istiyanti et al. (2020) revealed that kuroboku and scoria have different characteristics, whereas the Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 6 of 13 Fig. 4 Plan section and cross section on research areas; a Towa landslide, b Mizuho landslide (Geospatial Information Authority of Japan 2020) Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 7 of 13 Fig. 5 Soil stratigraphy on the field, soil hardness, physical properties, and saturated permeability properties values in research area with dotted lines indicate sliding layer by field observation; a Towa landslide, b Mizuho landslide sliding layers (N3-4 kuroboku (L) layers) have the high- while those of earthquake-induced landslides on tephra est plasticity index and liquid limit values and are plotted at Hokkaido have non-plastic soil. in the kuroboku group on the plasticity chart. Therefore, Furthermore, the plasticity chart divided the tephra the sliding layers of heavy rainfall-induced landslides on materials from the Towa and Mizuho landslides into tephra at Aso volcanic mountains have high plasticity, three types: inorganic silts of medium compressibility and organic silts, inorganic silts of high compressibility Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 8 of 13 Fig. 6 Particle size distribution curves of tephra materials organic clays, and non-plastic (NP). The kuroboku the older tephra materials probably have higher liquid and Ta-c L layers from the Towa landslide, including limit and plasticity index values, if the tephra materials the Loam (En-a) U and Loam (En-a) L layers from the are very old, they probably do not have plasticity values, Mizuho landslide, are inorganic silts of medium com- i.e., they belong to the NP soil. Unfortunately, a different pressibility and organic silts with lower liquid limit and result was obtained for the Ta-c U layer, which belongs plasticity index values. Furthermore, weathered Ta-d, to the NP soil, although the Ta-c U layer was not an old Ta-d U, and Loam (En-a) layers from the Towa landslide tephra material. and weathered Ta-d layer from the Mizuho landslide are inorganic silts of high compressibility and organic clays Saturated permeability properties with higher liquid limit and plasticity index values. The Figure  5a, b show the saturated permeability properties NP group consists of Ta-c U and Ta-d L layers from the of the tephra materials. This study measured the satu - Towa landslide and En-a U, En-a L, and Loam (Spfa-1) rated permeability properties of each tephra layer from layers from the Mizuho landslide. the Towa landslide and on the En-a U, En-a L, and Loam The plotted data on the plasticity chart also shows three (Spfa-1) layers from the Mizuho landslide. A significant groups of tephra materials: scoria (N2 scoria: 1.5  ka and peculiarity was observed in the Ta-d U layer of the Towa OJS scoria: 3.6 ka), kuroboku, and Ta-d (8.7–9.2 ka); the landslide. The Ta-d U layer exhibited the highest water chart is possibly related to the age of the tephra materials. content, coefficient of saturated permeability, and void The scoria group with the youngest age has lower liquid ratio with the lowest dry density value. The different limit and plasticity index values than the Ta-d group. The characteristics of saturated permeability in the Ta-d U Ta-c L layer (2.5 ka) was also included in the scoria group layer could be related to the different events in the Ta-d because it is almost similar to the scoria. Moreover, the layer. Different characteristics of saturated permeability oldest tephra material, the En-a layer, was NP. This study were also observed between the sliding and the under assumed that young tephra materials probably have layers. The dissimilarity in the void ratio and dry density lower liquid limit and plasticity index values; although indicated that the sliding layers have a loose structure. Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 9 of 13 Fig. 7 Ellipse pattern from plotted data of tephra materials in Aso volcanic mountains (Istiyanti et al. 2020) and plotted data of tephra materials from Hokkaido on plasticity chart Although the pore water pressure did not affect the land - Characteristics of soil physical properties on the sliding slides, the loose structure on the sliding layers could have layer influenced the landslides. During the earthquake, sliding The sliding layer on earthquake-induced landslides is a layers with loose structures easily collapse. Chang et  al. NP soil with a low density of soil particles, void ratio, and (2020) reported that loose materials accumulated on the dry density. The physical properties of the sliding layer slopes are more likely to fail during an earthquake. showed that the sliding layer is a stiff soil with a loose Furthermore, the relationship between the void ratio structure. Furthermore, the sliding layer on earthquake- and the coefficient of saturated permeability (Fig.  8) indi- induced landslides has a halloysite, which could have cated the dissimilarity in tephra layers. Although Ta-d affected the layer during the earthquake. This is because layers from the Towa landslide have several void ratios, the presence of the halloysite indicates that it is poten- the Ta-c, En-a, and Loam layers have a narrow range of tially weak, which explains the appearance of shrinkage void ratios. The Ta-d U and En-a layers from the Towa cracks (Moon et al. 2015). and Mizuho landslides have a considerable coefficient of Therefore, the characteristics of the sliding layer on saturated permeability, respectively. Shimizu and Ono tephra materials in earthquake-induced landslides are (2016) determined the saturated permeability proper- stiff soil with a loose structure, and the halloysite con - ties of tephra layers from the Aso volcanic mountain area tent in the sliding layer triggers shrinkage and cracks and reported that the hydraulic conductivity at the layer in the layer. During the earthquake, the loose structure below the sliding layer in heavy rainfall-induced land- and cracks on the sliding layer could not handle the driv- slides was decreased, and the difference in hydraulic con - ing force, i.e., the mass of the upper layers, causing the ductivity affects the tephra layer. Because the landslides landslide. in this study were triggered by an earthquake, no differ - ences in hydraulic conductivity were found between the sliding and under layers. Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 10 of 13 Fig. 8 Correlation between coefficient of permeability (m/s) and void ratio Content of clay minerals and halloysite (kaolinite group). Furthermore, the En-a The USGS  (2001) classified clay minerals into seven layer contains illite, chlorite, montmorillonite (smectite groups in its laboratory manual for XRD:chlorite, illite, group), and kaolinite group (dickite and halloysite). kaolinite, mixed-layer clays, smectite, sepiolite, palygor- There was no significant difference in the content of skite, and vermiculite. The clay minerals in the tephra lay - clay minerals in the tephra layers of the Mizuho land- ers from the Towa landslide generally contained smectite slide. Additionally, the Ta-d L layer from the Towa land- clay minerals (Fig.  9a). Kuroboku layers contain chlorite, slide contained a halloysite, whereas other tephra layers illite–smectite, and montmorillonite (smectite group). in the Towa landslide did not. Chigira et  al. (2018) and Furthermore, the Ta-c U, Ta-c L, and Loam (En-a) layers Koyasu et al. (2020) confirmed the presence of halloysite contain montmorillonite (smectite group). The weath - in tephra layers. Chigira et  al. (2018) confirmed that the ered Ta-d layer contains chlorite and montmorillonite sliding layer is at the Ta-d layer, which has a halloysite, (smectite group), and the Ta-d L layer contains halloysite and that a large amount of water is contained within the (kaolinite group) and montmorillonite (smectite group). halloysite formation. Surprisingly, this peak was not observed in the Ta-d U layer. Conclusion The clay minerals in the tephra layers from the Miz - According to previous studies, the physical properties uho landslide generally contained smectite and kaolinite of sliding layers from two landslides revealed the same clay minerals (Fig.  9b). The weathered Ta-d layer con - characteristics, NP soil with low density of soil parti- tains illite, chlorite, smectite group (montmorillonite and cles, void ratio, and dry density, and these characteristics smectite), and kaolinite group (dickite and halloysite). could influence earthquake-induced landslides. Further - The Loam (En-a) U layer contains illite, chlorite, mont - more, the sliding layer contains halloysite, which could morillonite (smectite group), and halloysite (kaolinite have caused cracks. This study revealed that the charac - group). The Loam (En-a) L layer contains illite, chlorite, teristics of physical properties influence the sliding layer. illite-montmorillonite, montmorillonite (smectite group), During the earthquake, the loose structure and cracks in Istiy anti and Goto Geoenvironmental Disasters (2022) 9:21 Page 11 of 13 Fig. 9 Clay minerals on tephra materials from Towa and Mizuho landslides Istiyanti and Goto Geoenvironmental Disasters (2022) 9:21 Page 12 of 13 Received: 31 January 2022 Accepted: 30 September 2022 the sliding layer could not handle the driving force, which is the mass of the upper layers, thereby triggering the landslide. The physical and saturated permeability properties References of the Towa landslide also indicated different charac - Arthurs JM (2010) The nature of sensitivity in rhyolitic pyroclastic soils from teristics of the Ta-d U layer. This phenomenon could be New Zealand. 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Journal

Geoenvironmental Disasters – Springer Journals

Published: Oct 14, 2022

Keywords: Earthquake; Physical properties; Shallow landslide; Sliding layer; Tephra materials

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