HDS25-P01

Room:Convention Hall

Time:May 27 18:15-19:30

Origin of hummock swarm developed in Kamenoharaike landslide of Oki Dogo, Shimane
Prefecture
ISHIBASHI, Aika1∗ ; MURAKAMI, Hisashi2 ; YOKOYAMA, Shunji1
1

Kochi University, 2 Cosmo Construction Consultants Co.Ltd

In the Tsuma district, Okinoshima-town located in the southwestern part of Oki Dogo, several landslides, occurred in Omosu
Formation mainly of trachyte and rhyolite lava interbedded rhyolitic tuff, are characterized by swarm of elongated, rounded
hillocks around small valleys .
Our investigated Kamenoharaike landslide is one of them and has a triangle shaped moving body which is about 2.5km longto the toe and maximum 2.0 km wide at the main scarp. From the topography of the moving body it estimates that the dip angleof sliding surface is approximately less than 5 degrees.
At Kamenoharaike landslide we found many hillocks consisting of jointed hard lava of trachyte or rhyolite, and some outcropsof soft clayey rhyolitic tuff underlying the lava with high water content. This two-storied house structure suggests existence of
cap rock structure of upper hard layer of trachyte or rhyolite lava and lower soft layer of rhyolitic tuff before slope movement.
Interpretation of landslide landform used for topographic map at a scale of 1:25000 and aerial photographs at a scale of
1:10000 has revealed that the moving body of Kamenoharaike landslide is separated from about 30 hummocks many of which
are arranged parallel or sub-parallel to the main scarp. The hummocks has a range from 50 to 500m in length and from 20 to
200m in width, and the top of hillock rises from 10 to 80 from the level of valley bottom. The aerial shape shows a lozenge,
oval and parallel-tetragon. The existence of hummock swarm and their arrangement pattern coincide with topographic featuresof spread (one of movement type of landslides) demonstrated by Oyagi(2003).
Mountain area behind the main scarp is developed in deep linear depressions, suggesting existence of open cracks, parallel andsub-parallel to the directions of elongated hummocks in the moving body. From this fact, it is possible that formation of the linear
depressions is prior to movement of spread over the area of Kamenoharaike landslide. However as the two linear depressionsof east -west and the southwestern-northeast trend divide the main scarp into three segments, the linear depressions have been
active after the formation of the main scarp of Kamennonaraike landslide

Keywords: Oki Dogo, Landslide topography, Spread

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HDS25-P02

Room:Convention Hall

Time:May 27 18:15-19:30

Late Pleistocene to Holocene landslide dammed lakes formed around Lake Shibire, Misaka Mountains, central JapanSUZUKI, Terumi1∗ ; KARIYA, Yoshihiko2
1

Graduate School of Senshu Univ., 2 Senshu Univ.

At 2014 JpGU meeting, we preliminary reported the historical development of Lake Shibire based on the geological and geomorphological information (Suzuki et al. 2014; HDS29-P06). In particular, we showed the sedimentological and chronologicalfeatures of a paleolake (paleolake A; PLA) that was connected with the present Lake Shibire and had survived during the period
from 47 to 30 cal ka. At 2015 JpGU, we account for new 14 C dates of the lacustrine sediments of PLA, and for the newly
discovered lacustrine sediments formed by another paleolake.
New 14 C samples were obtained from the middle and the uppermost positions of PLA sediments, whereas the bottom age of
PLA sediments was already decided as 47-46 cal ka. These samples indicated 42-41 cal ka and 3.1-3.0 cal ka, respectively. We
should pay careful attention to unconformity (unidentified at present) between the middle and upper parts of PLA sediments.
However, it can be estimated that PLA had survived for longer than ever thought. In the late Holocene, PLA would have shrunkand had landscape of wetland or gradual channel.
Other lacustrine sediments were found from the outcrop localities about 1 km south of the present Lake Shibire. These sediments continue horizontally and can be observed at least four outcrop localities at the same altitude (700 m ALS). This altitudinalconcentration of these sediments is obviously different from that of PLA sediments. Judging from these facts, we consider thatthese sediments were formed by another paleolake (paleolake B; PLB). Although the age and total thickness of PLB sediments
are uncertain at present, the estimated area of PLB is 0.05 km2 . Our geomorphic analysis suggests that PLB was caused by thesecondary landslide generated from the primary landslide body that created the paleo Lake Shibire and PLA.
Furthermore, we will attempt to show the preliminary description for drilling cores being recovered (as of Feb. 2015) from alacustrine terrace along the present Lake Shibire.

Keywords: landslide, dammed lake, lacustrine sediments, 14C date, late Pleistcene

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HDS25-P03

Room:Convention Hall

Time:May 27 18:15-19:30

Landslides in Aoki Village, Nagano Pref., Japan : Their distribution and geologicalgeomorphological characteristics
KOMIYAMA, Shoko1∗ ; KARIYA, Yoshihiko2 ; IWATA, Shuji3
1

Undergraduate at Senshu University., 2 Senshu University., 3 Tokyo Metropolitan University.

Many landslides are present in the Aoki Village of Nagano Prefecture where the Neogene sedimentary rocks and rugged mountains are dominant. Nevertheless, little attention has been paid to the distribution, topographies, and ages of landslides in thisvillage. We investigated the landslide geology and geomorphology of the village on the basis of airphoto interpretation, field
mapping of geology, and tephrochronology of landslides as well as GIS-aided geomorphic analysis.
A sum of 109 landslides was identified. A total area of those landslides attains 12.3 km2 , occupying 21.5% to the total areaof the village. Six landslide complexes comprising an assemblage of landslide bodies were also distinguished. Landslide distribution generally coincides with lithology of bedrocks. In particular, cleavable the Bessho Formation of shale seems to be prone
to landslide occurrence. A cap rock structure and dip-slope strata are also thought to be crucial factors. These suggest that rockcontrol is effective to generate landslides in the study area.
We found faulted and folded tephra layers with high content of hornblende, quartz, and biotite covering the Irinaramoto Landslide Complex (INM) that is a widest and most typical landslide in the village. Stratigraphic position and mineralogical propertiesof these tephra beds suggest that these tephra layers can be correlated with the Omachi APm during 350-300 ka. This fact showsthat the primary or secondary landsliding of the INM would occur after the middle Pleistocene despite their triggers are uncertain.

Keywords: Neogene system, Tephrochronology, Omachi APm tephra group, Cap rock, Rock control, Dip slope landslide

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HDS25-P04

Room:Convention Hall

Time:May 27 18:15-19:30

Geomorphic and geologic features of the Holocene catastrophic rock avalanche in Yabusawa Valley, Akaishi Range, Japan
KUROSAWA, Hiroshi1∗ ; KARIYA, Yoshihiko2 ; MATSUSHI, Yuki3 ; MATSUZAKI, Hiroyuki4
1

Graduate School of Senshu University, 2 Senshu University, 3 Kyoto University, 4 University of Tokyo

To determine the cause and age of thick gravel layers called the Yabusawa Gravel (YG) in the northern face of Mount Senjo(3033 m ASL), we reinvestigated geology and geomorphology of the YG. Although the previous authors considered that the YG
was of glaciofluvial or of landslide origin, there is no clear consensus as to the origin and age of the YG.
The YG consists of poorly-sorted thick angular clasts of sand stone, mud stone, and hornfels, forming a geomorphic feature
like fluvial terraces along Yabusawa Valley. On the outcrop walls of the YG, rock clasts clearly exhibit jigsaw crack structures,
although specific sedimentary facies reflecting fluvial processes such as lamination and imbrication are not observed at all. A
lithotype of rock clasts in the YG is almost restricted to single geology at a given outcrop locality. Surficial topography of the
YG has hummocks and levee-like terrain. A mountain ridge and valley side slopes adjacent to the YG have ridge-top linear depressions, untiscarps, and valley bulging, suggesting deep-seated gravitational slope deformation. Terrestrial cosmogenic nuclide
dating of sandstone fragments obtained from three localities on the depositional surfaces of the YG shows 10.3-8.4 ka, 10.0-8.1
ka, and 9.4-7.6 ka (in 10 Be scale). On the basis of these facts, we concluded that the YG was produced by catastrophic rockavalanche (rock slide) in the early Holocene. The previous authors emphasized degradation of mountain permafrost for landslide
occurrence, we invite attention to paleoearthquakes caused by nearby active faults or convergent plate margins as well as early
Holocene pluvial climate and long-term gravitational rock deformation.

Keywords: Rock avalanche, Deep-seated gravitational slope deformation, Terrestrial cosmogenic nuclide dating, Holocene

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HDS25-P05

Room:Convention Hall

Time:May 27 18:15-19:30

The Relationship between the Development of Slip Surfaces and Small Scarps on DeepSeated Catastrophic Landslides
YOKOYAMA, Osamu1∗ ; OGAWAUCHI, Yoshito1 ; YAMAZAKI, Tsutomu1 ; SAKURAI, Wataru2 ; SAKAI, Ryo2 ;OKUYAMA, Yuki2 ; KITAGAKI, Hirofumi2 ; HIRANO, Go3
1

Japan Conservation Engineers & Co., Ltd., 2 Sediment Disaster Prevention Technology Center, Kinki Regional Development
Bureau, MLIT, 3 Kii Mountain District Sabo Office, Kinki Regional Bureau, MLIT
To predict the occurrence of deep-seated catastrophic landslides in advance, it is effective to recognize the surface topographythat has preceded the catastrophic landslide. Recently, it has become possible to obtain high-resolution DEMs using the airborne
laser scanner survey (LiDAR). However, in areas where mountains have high relief and fractured sedimentary rocks, large-scale
gravitational slope deformation proceeds in a wide area, while topography, such as linear depressions and uphill and downhillfacing scarps, becomes sufficiently developed. Thus, in just recognizing deformed topography, it is difficult to identify highrisk catastrophic landslides. Therefore, it is necessary to determine the relationship between the internal geological structure
and the geometry, and differentiate geomorphological features by standards to predict the location, scale, and occurrence timeof catastrophic landslides. In this study, we clarify the geomorphological and geological features of a deep-seated catastrophic
landslide (Akadani) that occurred on the Kii Mountain because of heavy rain in 2011. Additionally, we examined the relationshipbetween the slip surface and the small scarp.
It is considered that the shear proceeds in the brittle fracture zone of a minor fault, and that the weak layer of the slip surface isformed in the creeping rock mass. Also, several meters of the small scarp were formed before the catastrophic landslide, and areconsistent with the outline of the catastrophic landslide. In fact, the shear plane came out of the ground by concatenating minor
faults that were located intermittently in the mass rock. In addition, large scale planar structures, such as a thrust or high-angle
fault, controlled the outline of the catastrophic landslide. Kawarabi and Nagatono, adjacent to Akadani, also have many similar
points that are made up of the same geomorphological and geological structures.

Keywords: deep-seated catastrophic landslide, slip surface, minor fault, gravitational slope deformation, small scarp, LiDAR

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HDS25-P06

Room:Convention Hall

Time:May 27 18:15-19:30

Distribution of trigger and relationship between trigger and geology of deep-seated landslides
IIDA, Tomoyuki1∗ ; YAMADA, Ryuji1
1

National Research Institute for Earth Science and Disaster Prevention

In the Shimanto accretionary complex in the southwest Japan, most of the recent deep-seated landslides (DSLs) were inducedby heavy rainfall over 1000 mm in a few days. In contrast, in the areas of Neogene sediments in the northeast Japan, recent
DSLs were induced by strong seismic motion larger than six on the Japanese earthquake damage scale. These facts imply thatthe regional characteristics exist in the factors that induces DSLs (i.e., rainfall or earthquake), and that these factors are related
strongly to the geological features of DSL sites. We therefore studied the regional characteristics of rainfall and earthquake on
the basis of the distribution maps of rainfall probability, active faults and earthquake epicenters in Japan.
The processes of DSLs induced by two factors and the geological influences on them are summarized as follows. In the
Shimanto accretionary complex in the southwest Japan, DSL induced by heavy rainfall is more likely compared with that byearthquake. This is because of the higher precipitation in the relevant area and the convergence of seepage water into the cracksof potential slip surfaces formed by rock creep. Earthquake-induced DSL is unlikely because active faults in this region are
few and the mountainous basement is relatively hard. On the other hands, in the Neogene sediments in the northeast Japan,
rainfall-induced DSL is unlikely because of the lower precipitation and the divergence of seepage water due to porous media.
Earthquake-induced DSL is likely because earthquake stimulates greater ground motion in the Neogene sediments and the mountainous basement is relatively soft.

Keywords: deep-seated landslide, trigger, geology, heavy rainfall, strong earthquake

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HDS25-P07

Room:Convention Hall

Time:May 27 18:15-19:30

Study on developing process of valley by deep-seated catastrophic landslides
YOSHINO, Kosuke1∗ ; UCHIDA, Taro2
1

Asia Air Survey Co., Ltd., 2 National Institute for Land and Infrastructure Management

The Typhoon Talas (T1112) induced many large and deep-seated landslides in the Kii Peninsula. The Shimanto group (anaccretionary complex) is widely distributed on the Kii Peninsula, and deep-seated landslides are known to occur often in thiskind of accretionary complex. Also, many of the deep-seated landslides caused by Typhoon Talas occurred on dip slopes, and itis thought that such geological structures also had a possible factor to the occurrence of deep-seated landslides. However, until
now, there was no widely used physical-based model for describing deep-seated landslide rapid (catastrophic) occurrence.
Recently, we have proposed a physical-based model for describing the process of widening water channel that accompanies
the overtopping erosion of landslide dams. In the model, we assumed that the channel widening was induced by side slope
collapses due to channel bed degradation, and we used slope stability analysis to describe side slope collapse. We confirmed thatthe proposed model was able to effectively describe the side slope geometry of water channels of actual landslide dams.
We considered that there is the possibility that the development process for valleys that occur with deep-seated landslides canalso be describe during our proposed model. Accordingly, in this study, with the deep-seated landslides caused by Typhoon Talasand the slopes where did not occur as our focus, we used the detailed topological data (LiDAR data sets) measured before andafter Typhoon Talas to sort bank grades and relative heights, and to evaluate the applicability of the model.
As a result, for areas where geological structures and soil strength were thought to be generally uniform, the relations between
gradient and relative height of side slope of Tostugawa River were effectively described by the proposed model. This seems tosuggest the possibility of using fundamentally measurable physical values to predict, to a degree, the slopes that are at risk ofdeep-seated landslides and the scale of those landslides.
Keywords: Deep-seated catastrophic landslides, Slope stability analysis, Soil property, Typhoon Talas (T 1112), Kii peninsula

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HDS25-P08

Room:Convention Hall

Time:May 27 18:15-19:30

Geomorphological and geological features of landslide lobes in the Dakesawa basin, theKamikochi Valley of Japanese Alps
KIDA, Chizuru1∗ ; KARIYA, Yoshihiko2 ; YAMAMOTO, Nobuo3 ; HARAYAMA, Satoru4 ; TAKAOKA, Sadao2 ;SHIMAZU, Hiroshi5
1Graduate School of Senshu Univ., 2 Senshu Univ., 3 Res. Grp. Nat. Hist. in Kamikochi, 4 Shinshu Univ., 5 Rissho Univ.

The Dakesawa basin is a stream tributary to the Azusa in Kamikochi Valley. It is believed that the whole of Dakesawa basin
was formed by the Pleistocene glaciations. However, no direct evidences such as moraines have been found. In the Dakesawa
basin, steep valley side slopes with sparse vegetation and wide valley floor with recent debris flow tongues are prominent. The
Dakesawa basin is composed of welded tuff, diorite porphyry, and granodiorite. A large lobate form (DLB; 270 m wide, 370 mlong, estimated volume 1.9×105 m 3 ) is present in the lowermost part of the Dakesawa basin. DLB is composed of two smaller
lobes whose altitudes are different (DLB-h and Dlb-l). DLB seems to continue to a wedge-shaped steep valley head whose
geology is restricted to granodiorite. This valley head is situated at a peripheral convex break of gentle slopes with features ofdeep-seated gravitational deformation. Also DLB is arranged to cover the present debris flow tongues on the valley floor of theDakesawa basin. Surface of DLB-h and Dlb-l is composed of a pile of megaboulders (>2-10 m in diam.) showing block fields
with open-work textures. Restrictive lithology of these boulders to granodiorite is obvious. A possible cause of DLB is rockslidethat occurred on the nearby valley head. Fallen materials would spread on the valley floor of the Dakesawa basin. Although
the age of rockslide is measuring in progress, the Holocene epoch is practical certainty because of its stratigraphic relationships
between recent debris flow tongues.
Keywords: Bedrock landslide, Deep-seated gravitational slope deformation, Block field, Holocene

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HDS25-P09

Room:Convention Hall

Time:May 27 18:15-19:30

Development history of concentrated sackung features around northern tip of the active
Neodani fault, central Japan
KOMURA, Keitaro1∗ ; KANEDA, Heitaro1 ; KOJIMA, Satoru2 ; IWAMOTO, Naoya2 ; HAYASHI, Hoshikazu1
1

Department of Earth Sciences, Chiba University, 2 Department of Civil Engineering, Gifu University

Suckung features such as linear depressions and up-hill-facing scarps are receiving attention as precursors of deep-seatedlandslides. Recent high-resolution airborne LiDAR revealed that many sackung features are concentrated around the northern
tip of the active Neodani fault, central Japan. These features are hidden under forest canopies, and thus high-precision dating of
deformation episodes would be feasible by AMS-14 C ages from carbon-rich sediments that fill sackung depressions, which is a
big advantage over previous similar studies in alpine areas. In order to examine the relation between the fault activity and theformation of these features, we conducted hand auger coring (down to 1.5-3.4 m depth) and pit excavation (down to 1.5 m depth)
at five sites out of ˜20 gravitational depressions that occurred in our study area.
On the basis of AMS-14 C ages of leaves, seeds, and twigs collected from peaty and lacustrine sediment as well as resultsof tephra analysis, it proved that all studied depressions were formed after the last glacial, but the formation ages vary fromdepression to depression: the oldest one was formed ˜11,000 years ago whereas the youngest one occurred ˜2,000 years ago.
In addition, our pit excavations revealed that the sediments are deformed after their deposition, suggesting that some of thesackung scarps grew at least twice after ˜3,600 years ago, and the most recent growth may have occurred associated with the1891 Nobi earthquake on the Neodani fault. Multiple Holocene events of sackung-scarp formation and growth are consistent
with earthquake recurrence interval of the Neodani fault (˜2000-5000 years), so they may have a synchroneity.

Keywords: sagging, sackung, active fault, Mino mountain, AMS-14C ages, tephra analysis

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HDS25-P10

Room:Convention Hall

Time:May 27 18:15-19:30

The mechanism of strain rate strengthening during landslide
TAKE, Kotaro1∗ ; SAKAGUCHI, Arito1 ; SATAKE, Shinji2
1

Yamaguchi Univ., 2 Fukken co.,ltd.

Many landslides slip relatively slowly without catastrophic failure. The slip events happen when sporadic hard rainfall. Monitoring and disaster prevention measures are carried out in some landslide area. These monitoring records must be useful toelucidate landslide mechanism. This study shows detailed slip behaviors at landslide by monitoring records of landslide.
The study area is located in Hiroshima, southwestern Japan. The talus sediments are overlained by the mudstones of thebasement rocks. The mudstones include the basal slip fault of the landslide of several centimeters in width. In situ strain andgroundwater level were observed in five borehole sites. Ground surface movements were observed by extensometers. The
groundwater level increased immediately after beginning of the rainfall, and which trigger the landslide. The acceleration rate of
the landslide, decreased with slip velocity. This demonstrates strain rate strengthening.
Keywords: landslide, strain rate strengthening

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HDS25-P11

Room:Convention Hall

Time:May 27 18:15-19:30

Relationship between the wind damage caused by the 1959 Isewan Typhoon and the landslide that occurred afterwards
MURAKAMI, Wataru1∗ ; SAITO, Hitoshi2 ; DAIMARU, Hiromu1
1

FFPRI, 2 Kantogakuin Univ.

We investigated landslides caused by the later rain, on the slopes in the granite where forests were destroyed by typhoon.
Investigation area is located in Nagiso town, Nagano Prefecture. In Nagiso town, large-scale forest area was destroyed by the
Isewan Typhoon in 1959. First, we interpreted aerial photographs been filmed immediately after the typhoon and extracted winddamage zone. Second, we interpreted plural aerial photographs been filmed after the typhoon and extracted landslides occurredby the later rain. And then, we examined the relationship between forest damage zone by the typhoon and landslides by the later
rain, in conjunction with the topographic condition.
As a result, it was revealed that a lot of landslides occurred on the forest slope where the typhoon was damaged. Furthermore,
it was recognized that the slope where landslides occurred was tendency to gentle and southfacing.

Keywords: Isewan Typhoon, wind damage zone, landslide, aerial photointerpretation, granite rock

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HDS25-P12

Room:Convention Hall

Time:May 27 18:15-19:30

Detection the landslide deformation using InSAR analysis in the southern Japanese AlpsNISHIGUCHI, Takaki1∗ ; IMAIZUMI, Fumitoshi2
1Graduate School, Shizuoka University, 2 Faculty of Agriculture, Shizuoka University

It is important to identify the ground deformation areas by landslides for sediment disaster prevention. Since InSAR analysis
can investigate surface deformation in wide areas with accuracy of centimeters, it is effective for detecting on actively creeping
landslides. Aim of this study is detecting deformation of landslides using ALOS-PALSAR data and verifying the validity of
results based on the field survey. We conducted InSAR analysis in the Ikawa district located in the southern Japanese Alps,
central Japan. This area has weak geology because of fault belts named Median tectonic line and Itoigawa-Shizuoka tectonic
line. A lot of landslides have occurred due to existing steep topography and abundant precipitation (about 3100 mm/year).
We compared the results with landslide distribution maps that were constructed by aerial photograph investigations detecting
characteristic landslide topographies. As a result, by the InSAR analysis, some displacements of landslide bodies were extracted.
We detected clacks in road retaining walls by field survey at displacement points. We also conducted 2.5-dimensional analysis at
the areas in which displacement has been observed using images captured on both ascending and descending orbits.
Keywords: landslide, InSAR

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HDS25-P13

Room:Convention Hall

Time:May 27 18:15-19:30

About a large-scale landslide disaster of Hiroshima by the Airbone Lidar
KOBAYASHI, Hiroshi1∗ ; FUKUDA, Makoto1 ; NAKANO, Youko1 ; ABE, Misa1
1

Aero Asahi Corporation

In a large-scale debris flow disaster stricken area in Hiroshima-City that occurred on the early morning of August 20, 2014, I
carried out an aviation laser measurement and considered the characteristic of the mountain stream which produced the topography, a geological feature and a mud flood.The southwestern part was the sedimentary rock distribution area that rough grain- infinitesimal grain granite distribution area, the northeast side made a hornfels, and it became clear depending on geologicalfeature distribution in the detailed topography model in Yagi, the Midorii district in investigation places that valley density, therelative height distribution of the basin were different clearly. Similarly, in the Kabehigashi district, middle grain - infinitesimal
grain granite distribution area, the eastern part were Takada rhyolite distribution area the western part, and valley density, therelative height distribution of the basin were different depending on geological feature distribution clearly. Furthermore, it was
revealed that a real geological feature border was different from existing geologic map width (product research institute), but wasable to estimate it from a characteristic of the topography.The sections of a slow incline continued in the whole in the granite
distribution area of Yagi, the Midorii district when I compared the longitudinal section shape of the mountain stream in eachgeological feature distribution area, and only the most upper reaches region where the basin world was near became the steep
grade. On the other hand, an incline changed in the whole exponentially in the hornfels distribution area. Is the down stream fromthe neighborhood of valley exit; as for neither of the mud flood knew that flowed down, and sedimentation section considerable
inclines continued for a long time.After all, in the Kabehigashi district, the sections of the incline that the middle down stream
part was gentle continued with the granite distribution level, but the most upper reaches region was a steep grade very much. On
the other hand, in the rhyolite distribution area, I showed a characteristic like the hornfels distribution area. Is the down stream
from the neighborhood of valley exit; as for neither of the mud flood flowed down, and had a long it, and sedimentation section considerable inclines continued, but tended to be slightly in comparison with Yagi, Midorii district loose.At each mountainstream, it reflects that an alluvion drill develops from the neighborhood of valley exit that an incline of the down stream side isslow. In addition, at the mountain stream which faced Otagawa of the district at the north end directly in Yagi, Midorii districts,
I show a constant sudden vertical section incline, but, as for this, the end receives erosion of Otagawa, and it is thought that I am
connected with having been the environment that cannot form an alluvion drill.The above-mentioned mountain stream properties
are greatly related to the production situation of the earth and sand, the transportation situation, the sedimentation situation inthis disaster.
Keywords: granite, hornfels, rhyolite, longitudial profile of ravine, debris flow

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HDS25-P14

Room:Convention Hall

Time:May 27 18:15-19:30

Soil structure and shallow landslides on hillslopes underlain by granite and hornfels
WATAKABE, Takuma1∗ ; MATSUSHI, Yuki2 ; CHIGIRA, Masahiro2 ; TSOU, Ching-ying2 ; HIRATA, Yasuto1
1

Graduate school of science, Kyoto University, 2 Disaster prevention research institute, Kyoto University

In 22 August 2014, a heavy rainstorm triggered numerous shallow landslides and debris flows in hillslopes of granite andhornfels in Hiroshima, southwest Japan. The landslide density was larger in granite area than in hornfels area even they received
almost same rainfall amount (˜150 mm/3h). Soil thickness on hornfels was thicker than that on granite. We investigated hillslopewith shallow landslides to understand the difference in soil layer structure and soil properties. In the granite area, hydraulicconductivity ranged 10−5 -10−2 cm/s, decreasing gradually with increasing soil depth. In the hornfels area, hydraulic conductivity
ranged 10−8 -10−4 cm/s and impermeable layer emerged just below the slip surface. These results suggest that soil propertiesare different between granite and hornfels. The soil from hornfels contains finer in grain size, higher in clay and more cohesiveminerals than that from granite. These differences may affect the subsurface water behavior and slope destabilization process ineach area, and hence potential of shallow landsliding by heavy rainstorms.
Keywords: shallow landslides, granite, hornfels, soil stracture

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HDS25-P15

Room:Convention Hall

Time:May 27 18:15-19:30

The analysis of relation between scale and topography on landslides induced by earthquake
TANAKA, Yasutaka1∗ ; UCHIDA, Taro1 ; KAMBARA, Jun’ichi1 ; WATANABE, Sin2 ; OZAKI, Jun’ichi2 ;KUDOU, Tsukasa2
1

National institute for Land and Infrastructure management, 2 Sabo Engineering Co., Ltd

The scale and volumes of deep-seated catastrophic landslide are often very large. And the damage by deep-seated catastrophic
landslide is also often much. To reduce these hazards requires to estimate the place that deep-seated catastrophic landslides
occur. On landslide induced by earthquake, Uchida et al.(2004) showed that the formula consisting of topographic features andseismic motion is useful to extract the small landslide. Takezawa et al.(2013) selected slope relief as scale of slope. And thisarticle indicated that landslide susceptibility was confirmed by using slope relief. In addition, Sammori et al.(2012) suggested
that landslides induced by Iwate-Miyagi Inland earthquake were controlled by not only topography, but also geology and the
distance between landslides and earthquake fault. However few studies investigated the effect of geology, the positional relation
with landslide and earthquake fault, and topography on the scale and density of landslide induced by earthquake, especially thedifference between deep-seated catastrophic landslide and shallow landslide. From the above in this study we measured thedensity of landslides, landslide area, the ratio of landslide area, slope angle, and slope relief in the area divided with the distancefrom earthquake fault, positional relation between landslides and the earthquake fault and geological feature.
We select Iwate-Miyagi Inland earthquake as the research area. We divided the research area at intervals of 1km from theearthquake fault, positional relation between landslides and earthquake fault, and the difference of geological feature. Then wemeasured the area, slope relief and slope of landslides. At result the density of landslide area in the divided area where thedistance from earthquake fault is 1˜10km, and that is on earthquake fault, is much more than other area.

Keywords: landslide induced by earthquake, Iwate-Miyagi Inland earthquake

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