粒子法および衛星画像を用いた土石流災害の定量評価

筑波大学 (University of Tsukuba)201

Controls on the distribution of landslides triggered by the 2008 Wenchuan earthquake, Sichuan Province, China

Landsliding is the dominant mass wasting process in upland areas where the rate of river incision is higher than that of rock weathering of hillslopes. Although progressive erosional processes can provide sufficient conditions for slope failure, the majority of landslides are induced by earthquakes, rainstorms or a combination of these two. Landslides are also one of the most destructive geological processes, being the primary cause of damage and fatalities associated with severe storms and earthquakes in mountainous regions. On 12th May 2008 the magnitude 7.9 Wenchuan earthquake occurred in the Longmen Shan mountain range, on the northwest margin of the Sichuan Basin. Landsliding contributed greatly to the high death toll of over 70,000 and widespread infrastructural damage produced by the earthquake. The event offers an opportunity to both broaden the global database of seismically induced landslides and study the processes involved in earthquake-triggered landsliding, for a large continental thrust event with complex faulting mechanisms and diverse geophysical conditions. To achieve this, the following investigation builds upon recent advances in landslide remote sensing, to develop automated detection algorithms through which landslides can be accurately mapped using a range of satellite data. Using these techniques, a first order, regional landslide inventory map of slope failures triggered by the Wenchuan earthquake is produced, over an area of 12,000km2 along the main rupture zone. The production of this dataset demonstrates the application of automated classification techniques for the rapid generation of landslide data, for both geomorphological research and hazard management applications. The data is used to examine the interaction of fault rupture dynamics, topography and geology on landslide failure location, and identify key characteristics of the landslide distribution. Findings of the study demonstrate high levels of landslide occurrence along the entire mapped length of the rupture zone, and an exponential decay in landslide density with distance from the co-seismic surface ruptures. This is superimposed over a marked hanging wall effect, along with clear geological and topographic controls on landslide occurrence. Through generalised linear modelling, peak ground acceleration attenuation patterns, hillslope gradient, relief, local elevation and geology are identified as core controls on the location of landslides. The results of this research shed light on some increasingly recognised though poorly understood characteristics of seismically induced landslide distributions. The dataset produced contributes to the limited global database of earthquake-triggered landslide inventories, as well producing a widely applicable resource for further study of the Wenchuan earthquake and post-seismic landscape evolution

Multi-scale analyses of granular flows for disaster resilience enhancement

A study that overlaps the fundamentals of granular flows with human responses to disasters at the community or regional scale is considered to be a strategic approach that advances existing methods in natural and human-induced hazard research in light of global-scale changes in earth systems. This study aims to improve the understanding: 1) on the mechanical behaviors of fluidized loess flowslide using centrifuge modeling as well as in-house designed laboratory testing and elastic wave characterization techniques (i.e. natural systems), and 2) on the cascading impacts of geohazards on local communities, assessing disaster resilience associated with reconstruction strategies and the performance of debris flow mitigation systems (i.e. natural-human systems interactions). The current work reveals the state-dependent effects of structure on flow behavior of loess and proposes modified criteria to predict the flow behavior. Laboratory tests show the changes in the mechanical behavior due to decementation of loess and indicate the needs to study loess within the scope of geotechnical analysis. The failure mechanism of loess flowslide is better understood from the study on the deformation process that shows the compounding effects of increasing pore-water pressure and reducing confining stresses on static liquefaction. The earthquake and post-earthquake impacts are documented after the 2008 Wenchuan earthquake, which permits a pilot study on quantifying the recovery processes of two communities of different reconstruction modes in light of Bayesian-based learning method. The design and performance of post-earthquake debris flow mitigation systems are reviewed; it offers a simple and robust data-driven approach to evaluate the effectiveness of debris flow mitigation systems at the regional scale.Ph.D

Geospatial Assessment of Coseismic Landslides in Baturagung Area

Java, the most densely populated island in Indonesia, is located on top of the most seismically active areas in Southeast Asia: the Sunda Megathrust. This area is frequently hit by strong earthquake. More than 3,300 M>5earthquakesoccurred between 1973-2014. The wide range of mountainous areas and high intensity of rainfall, make several part of the island one of the most exposed regions for coseismic landslides such as Baturagung area, the Southeast mountainous area of Yogyakarta Province. An integrated method between RS and GIS was used to conduct the vulnerability assessment due to the lack of the site specific slope instability analysis and coseismic landslides data. The seismic zonation of Baturagung area was obtained based on the analysis of Kanai attenuation. The geologic information was extracted using remote sensing interpretation based on the 1:100,000 geologic map of Yogyakarta and geomorphologic map of Baturagung area as well. The coseismic landslide hazard assessment has been estimated using scoring analysis in the GIS platform proposed by Mora and Vahrson (1993) with several modification. The accomplished coseismic landslide hazard map shows medium hazard coverage in the eastern areas, in the upper slope of Baturagung area, which consists of Semilir Formation. The result provides a distinct description of coseismic landslides hazard distribution in Batuaragung area. However, it should only be the preliminary assessment of the site specific investigation especially on valuable area or asset

‘Breaking New Ground’; An investigation into coseismic ground cracking following the 2016 Mw 7.8 earthquake near Kaikoura, New Zealand

Seismic shaking can cause landsliding throughout mountainous topography. Posing a direct hazard to the people and infrastructure that occupy these environments, landsliding receives considerable attention from the scientific community. However, few studies have detailed and analysed another form of earthquake-induced damage – ground cracks. Cracks could be a potential indicator of incipient landsliding and/or a surface expression of the retention of damage by hillslopes. Existing damage makes hillslopes more vulnerable to future failure. As such, ground cracking poses a lingering hazard presenting a need to better understand it – in particular its geomorphological characteristics and most influential controlling factors, and therefore how it can be detected/modelled. In 2016 the Mw 7.8 Kaikoura earthquake in New Zealand resulted in extensive ground cracking, providing an ideal case study. A ground crack inventory was digitally compiled using visual interpretation of post-event aerial photography. A detection attempt using a post-event digital terrain model (DTM) to semi-automatically extract cracks was unsuccessful. However, comparing this with an attempt using higher-resolution sample data emphasizes the necessity to consider the interdependence between feature scale and data resolution when attempting to detect/analyse. Feature analysis found that cracks are preferentially 7 m (~3-8 m) in length. Lack of small features may be due to minimum strain thresholds and strain accumulation. Larger cracks have likely developed into landsliding. Both offer new insight into internal hillslope forcing. Cracks preferentially form in a slope perpendicular direction, indicating a topographic control on propagation. Further potential controls were statistically analysed using Fuzzy Logic, which then informed a spatial prediction. The most influential control is proximity to landsliding, suggesting that in most cases cracking is an expression of incipient landsliding. Cracking preferentially occurs at ridgetop locations and on hillslopes facing the source of shaking. The latter is the inverse of behaviour exhibited by landsliding, highlighting the interdependence between directional shaking, local slope aspect and normal/shear stress. This conforms to and provides a new novel insight into the topographic site effects theory. Whilst quantitatively unsuccessful, the best performing spatial prediction model showed great promise in locating ground cracks in areas of high hazard, providing a solid foundation for improvement through further research so that eventually models like this can better inform ongoing hazard monitoring

Progress in Landslide Research and Technology, Volume 1 Issue 1, 2022

This open access book provides an overview of the progress in landslide research and technology and is part of a book series of the International Consortium on Landslides (ICL). The book provides a common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020, which is expected to continue up to 2030 and even beyond to globally promote the understanding and reduction of landslide disaster risk, as well as to address the 2030 Agenda Sustainable Development Goals