Shuichi Hasegawa

A replication of landslide hazard mapping at catchment scale

Landslide hazard assessment is a primary tool to understand the basic characteristics of slopes that are prone to landslides, especially during extreme rainfall. In this study, weights-of-evidence modelling a bivariate statistical method, and a logistic regression model, a multivariate statistical method, were used for landslide hazard mapping in two catchments of the Siwaliks in the Nepal Himalaya. Two typical catchments, Charnath and Jalad of the Siwaliks in easternNepal, were selected for the landslide hazard mapping. Both modelling approaches were applied by considering 10 intrinsic factors and one extrinsic factor. Mainly digital elevation model-based causative factors and field data were used to prepare data layers of landslide causative factors. In many approaches formodelling of landslide hazard in GIS, the model validation process is always dependent, and landslide data, which are used to calculate a landslide hazard index (LHI), are applied for verification. However, in this study, the LHI was calculated in one catchment (Jalad) and the same index for a different class of causative factors was applied for another catchment (Charnath), and the LHI wasverified. The verification results were very promising, with an independent prediction rate of about 75%. This validates weights-of-evidence and logistic regression models for landslide hazard assessment in the Siwaliks Range of Nepal.

Areal distribution of large-scale landslides along highway corridors in central Nepal

Landslides are the most frequent natural disaster in Nepal. As such, the scientific study of the Nepal landslides has been in progress for several years, but no significant achievement has been made in preventing landslides and mitigating disaster damage yet. As one important aspect of dealing with landslides is understanding their distribution pattern based on geological and geomorphological formations, this paper addresses these issues, and attempts to present a scenario of large-scale landslide distribution along the road corridors of major highways in central Nepal. As a result of landslide mapping using aerial photographs, topographical maps and field verification, the following points were understood: (1) the distribution of large-scale landslides is relatively dense over the area close to tectonic thrusts; (2) slate and phyllite zones have a greater ratio of landslide distribution; and (3) topographies with a mean slope angle of about 27–36 degrees have denser distribution of large-scale landslides.

Earthquake-Induced Landslides in the Roadside Slopes of East Nepal After Recent September 18, 2011 Earthquake

Being located in central part of the Himalayan ranges, Nepal is regarded as one of the earthquake-prone countries in the region. Earthquake is a major concern of Nepal because of rapid population growth, poor land use planning, precarious settlement patterns, and poorly implemented building code. Earthquakes in Nepal have been reported since 1255 while major earthquakes were recorded in 1408, 1681, 1810, 1833, and 1866, 1934, 1980 and 1988. Recent earthquake of September 18, 2011 measuring 6.9 in Richter scale killed 6 people and injured 30 people in Nepal. There were many roadside slope damages near the epicenter area. To assess the roadside slope damages after this earthquake, a field visit was conducted and a landslide inventory map along the roadside slope was prepared for the most problematic area. For this study, Koshi and Mechi highways of eastern Nepal were selected as study area and earthquake-induced landslides on the roadside slopes were evaluated in terms of characteristics and mode of occurrences.

Estimation Method of Amount of Tsunami Disaster Wastes during the 2011 off the Pacific Coast of Tohoku Earthquake

A huge amount of disaster wastes was accumulated along coastline areas of the Tohoku region by tsunami dur ing the 2011 off the Pacific coast of Tohoku Earthquake. Th e total amount of tsunami disaster wastes was estimated to be 26.7 million tons. This corresponds to 50 % of the total amount of the waste of Japan in 2009. Tohoku Earthquake caused widespread serious damage. Since the coastal area o f Tohoku region shapes a saw-toothed coastline, it is difficult to prepare large places for filling these disaster wastes. And a road for carrying to these treatment facilities i s not enough in Tohoku coast line area, most port facilit ies were damaged seriously. This means the dispose of disast er wastes is in extremely difficult in Tohoku region. Since a tsunami height in Shikoku region during nex t Tokai Earthquake or Nankai one will be larger than the Tohoku Earthquake, it can be anticipated that an am ount of disaster wastes in Shikoku is also very large. It i s very important to estimate an amount of tsunami disaster wastes for quick recover and revival of damaged areas. This paper describes a method of wastes amount estimation based on the officially announced data a nalyzed in GIS platform.

A method for regionally mapping gravitationally deformed and loosened slopes using helicopter-borne electromagnetic resistivity data

Earthquake-induced deep-seated landslides are prone to occur at gravitationally deformed and loosened slopes. These slopes need to be identified for landslide susceptibility mapping and landslide risk assessment. Surface morphology is an effective factor for finding the slopes, but is not effective for estimating the degree and the area of loosening. Subsurface geophysical investigations are quite useful for determining subsurface geological structures in regions where loosening has occurred. In this study, a method was developed for regionally mapping gravitationally deformed and loosened slopes as earthquake-induced deep-seated landslide susceptible zones by differentiating from sound bedrocks in flexural toppled slopes. Using the helicopter-borne electromagnetic resistivity data, “average ruggedness of resistivity” was proposed as an index parameter for differentiating the loosened zones. The estimated loosened zones were compared with observed geomorphological features during field survey, and it is shown that “average ruggedness of resistivity” is a useful parameter for regional mapping of earthquake-induced deep-seated landslide susceptible slopes.

Hazard Mapping of Earthquake-Induced Deep-Seated Catastrophic Landslides Along the Median Tectonic Line in Shikoku by Using LiDAR DEM and Airborne Resistivity Data

Shikoku Island has been threatened by great earthquakes occurred along the Nankai Trough and the Median Tectonic Line. Estimated magnitude of the largest earthquake along the Nankai Trough is estimated 9.0. Estimated magnitude of the Median Tectonic Line Earthquakes in northeastern part of Shikoku is 8.0 or more. The great earthquakes might trigger deep-seated landsides and the huge amount of landslide debris might paralyze transportation and isolate villages in mountainous areas. In order to mitigate the damage, estimating the hazard and preparation is necessary. In this study, index of susceptibility for earthquake-induced deep-seated catastrophic landslides is proposed geologically and geomorphologically.

Characteristic Features of Deep-Seated Landslides in Mid-Nepal Himalayas - Spatial Distribution and Mineralogical Evaluation

Landslides, primarily occurring in deep-seated landslide areas, frequently damage important roads in Nepal and contribute to massive economic losses and public suffering every year. Efforts to understand these landslides, which are often only regarded as geological phenomena, through material shear behaviour however remain insignificantly reported. In order to narrow this research gap, this paper first addresses spatial distribution of these landslides in about 150-km arterial road corridors in central Nepal, and then discusses their occurrence mechanism in terms of a relation between material shear strength and mineralogical composition. The deep-seated landslide inventory prepared out of the aerial photos and topo-sheets revealed that the landslide distribution is dominant in phyllitic and slate zones of geology while the laboratory tests on clay materials, sampled from 15 locations in the study area, in ring shear machine and x-ray diffractometer exhibited that the landslide soils, especially from the phyllitic area, possess comparatively high angle of shear resistance in a range of 20-30 degrees with remarkable influence of mica and chlorite composition, whose increased relative amount was found to result in notable decrease of the angle of shear resistance.

Susceptibility of slopes to earthquake-induced landslides: a new index derived from helicopter-borne electromagnetic resistivity and digital elevation data sets

In mountainous areas of Asia, huge earthquakes have triggered numerous landslides in recent decades. Estimating the susceptibility of slopes to landslide and the volume of potential landslide debris helps in planning for disaster risk management. We developed a new index to measure the susceptibility of slopes to earthquake-induced landslides by using helicopter-borne electromagnetic resistivity (HEM) survey data to quantify the looseness of bedrock and a digital elevation model to quantify the amplification of seismic waves by topography. In our study area around the Kanagi landslide (triggered by the 1707 Hoei earthquake), our new index showed that landslide susceptibility was low within the area of past landslides, but was higher in areas outside the scar of past landslides. Our results indicate that most of the loosened rock masses have been removed by past landslides, and the areas beyond the main landslide scar, where loosened bedrock remains, are now most susceptible to future earthquake-induced landslides. Our results indicate that this index may be effective in areas susceptible to landslides due to toppling failure and rock avalanches in loosened bedrock slopes.

Preservation of Sanukite, the Highly Sophisticated Music Instrument Made of Andesite

Sanukite is a special volcanic rock that had erupted about 13 Ma in northern Shikoku of southwest Japan. Petrologically it belongs to aphyric andsite. Sanukite is much harder and finer-grained than the ordinary volcanic rocks. Although its density is 2.60 g/cm3, its P-wave velocity is about 6 km/s. This high P-wave velocity is unique characteristics of sanukite. Dr. Hitoshi Maeda made the first stone xylophone (“sekkin” petrophone) in 1981. He has continued the analyses into the specific vibrational properties and wave forms of sanukite and he created many musical instruments of stone known by the name “Sanukitephone.” We believe that sanukite and Sanukitephones will be the future World Heritage. Sanukite is globally important rock and its resource is limited. As sanukite is the symbolic rock of Sanuki District (Kagawa Prefecture), we must hurry to establish preservation system as one of the member of the Global Geopark Network.

DISTRIBUTION OF LANDFILL BY GEOPHYSICAL EXPLORATION METHODS AT ILLEGAL INDUSTRIAL WASTES DISPOSAL SITE

Serious environmental pollution has caused by illegal disposal of industrial wastes in Kagawa Teshima Island, Kagawa Prefecture, Japan. For restitution of Teshima, a distribution of the industrial waste by the drilling survey by past administration’s research became clear roughly. But since the wastes was buried partially such as a pot into the sandy soil layer under the waste layer, it is necessary to investigate in detail the thickness of the wastes as removal of the waste layer progressed. In this paper, the surface wave prospecting, the microtremor, the Electromagnetic method (EM) sounding and the Continuous wave radar sounding, which is new geophysical exploration methods, were carried out at the illegal industrial wastes disposal site for the purpose of estimating the thickness of the waste layer with sufficient accuracy.