Abstract
On 6 September at 03:08 a.m. local time, a 33 km deep earthquake underneath the Iburi mountains triggered more than 7000 co-seismic mass movements within 25 km of the epicenter. Most of the mass movements occurred in complex terrain and became coalescent. However, a total of 59 mass movements occurred as discrete events and stopped on the semi-horizontal valley floor. Using this case study, the authors aimed to define planar and vertical parameters to (1) compare the geometrical parameters with rain-triggered mass movements and (2) to extend existing datasets used for hazards and disaster risk purposes. To reach these objectives, the methodology relies on LiDAR data flown in the aftermath of the earthquake as well as aerial photographs. Using a Geographical Information System (GIS), planform and vertical parameters were extracted from the DEM in order to calculate the relationship between areas and volume, between the Fahrböschung and the volume of the deposits, and to discuss the relationship between the deposit slope surface and the effective stress of the deposit. Results have shown that the relation S=k[Vd]2/3 (where S is the surface area of a deposit and Vd the volume, and k a scalar that is function of S) is k = 2.1842ln(S) − 10.167 with a R2 of 0.52, with less variability in deposits left by valley-confined processes compared to open-slope processes. The Fahrböschung for events that started as valley-confined mass-movements was Fc = −0.043ln(D) + 0.7082, with a R2 of 0.5, while for open-slope mass-movements, the Fo = −0.046ln(D) + 0.7088 with a R2 of 0.52. The “T-values”, as defined by Takahashi (2014), are displaying values as high as nine times that of the values for experimental rainfall debris-flow, signifying that the effective stress is higher than in rain-triggered counterparts, which have an increased pore pressure due to the need for further water in the material to be moving. For co-seismic debris-flows and other co-seismic mass movements it is the ground acceleration that “fluidizes” the material. The maxima found in this study are as high as 3.75.
Highlights
Introduction published maps and institutional affilThe world population is increasingly urban, leaving vast areas of ‘green deserts’ which are sometimes located at the door-step of human settlements
To create unbiased and comparable geometric relations of each mass movement, the mass movements sampled for the present study: (1) do not overlap with one another, because it is difficult to determine how one mass movement influenced the other, and; (2) do not run-up complex slopes, as once again the quantification of these effects is difficult to achieve with remote sensing
The authors present the geometrical relations between the morphological parameters and between the different shape indicators and factors, before ending with data on the distribution of the tree stems deposited over the sediments
Summary
Introduction published maps and institutional affilThe world population is increasingly urban, leaving vast areas of ‘green deserts’ which are sometimes located at the door-step of human settlements. In Hong-Kong, for instance, the proximity of the two has led to numerous mass movements taking the lives of more than 470 people since the 1940s [1]. Civil engineers have developed and implemented numerous geometric relationships, such as the angle of repose, to assess the hazardous zones (e.g., in Hong-Kong, China [2]). Geotechnical engineering is arguably a preferable approach, in remote areas and in countries where the population or the budget are decreasing, it has become essential to develop different methods which rely on lower-cost automated systems that can contribute to the further development of statistical approaches. The database analytics of the Enhanced Natural Terrain Landslide Inventory (ENTLI), which has 19,763 records in Hong-Kong, can contribute to developing such approaches [3]. The database analytics of the Enhanced Natural Terrain Landslide Inventory (ENTLI), which has 19,763 records in Hong-Kong, can contribute to developing such approaches [3]. iations.
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