Abstract:
Japan is a seismically active island nation and which has long been at risk of earthquakes
and related disasters due to its geological location. At the Japanese Standard Time (JST)
17:56 on October 23, 2004 an earthquake with a moment magnitude of 6.8 struck MidNiigata prefecture in Japan and caused many landslides and slope failures in the Chuetsu
region of Niigata prefecture. This catastrophic earthquake was followed by severe
aftershocks and caused many types of landslides such as surficial slides, shallow slides,
and deep slides. This study analyzed the correlations between landslide occurrence and
the slope angle, slope aspect, rock type, bedding plane orientation and dip, and distance
from the epicentre fault line by using landslide occurrence ratio (LOR), based on
geographic information system (GIS) technology. The LOR is defined as percentage of area
affected by seismic landslides. Surficial slides are correlated well with slope angle and
distance from the epicenter fault line. Shallow slopes that face parallel to the fault
direction are more prone to failure. In addition to that shallow slides occurrence ratio
decrease with distance from epicenter fault line. Deep slides are strongly affected by the
geological structure.
In addition, to examine the spatial distribution of earthquake-induced landslide, it is
essential to consider the seismic effects for designing slope stability, retaining walls,
bridges, and other engineering structures. It is important to determine the shear strength
parameters on a failure surface for stability evaluation and engineering analysis of a
landslide, as these parameters are mainly determined by the test, back analysis method
and engineering experience analogy method is used. Among these methods, the back
calculation is a procedure, which offers the opportunity to estimate the shear strength
properties along the failure surface by the mathematical method. Soil strength calculation
by back analysis avoids many of the problems related to laboratory testing and is widely
used, especially in association with landslide repair studies. This study presents the
rational procedure to calculate the horizontal seismic coefficient according to the distance
from the epicenter fault line and shear strength of the weathered soil. The seismic
coefficient is found similar with past research works.
