Risk of coseismic and post-seismic slope instabilities in relation with existing or causative faults: Fid-Bau Portal

Risk of coseismic and post-seismic slope instabilities in relation with existing or causative faults

Towhata, Ikuo

Abstract It is well known that coseismic landslides are likely to occur under stronger shaking at shorter epicentral distance under the effects of topography and amplification of shaking together with such local geology as rock and soil types. However, this paper addresses a different issue that is the role of faults played in the triggering of landslides, both coseismic and non-seismic, and the long-term slope instability that lasts for decades or centuries after devastating earthquakes. Experiences during and after gigantic landslides are important to understand what happens in and around faults. Noteworthy is that there are cases in which slope instability starts after earthquakes and lasts for some time along surface manifestation of faults, whether or not they are the causative fault. Another important issue is the recovery of stability in shallow parts of slopes. Experiences in Japan, Taiwan and China suggest that a few decades is needed for this re-stabilization. Discussion is further made of geologically generated ground water pressure that is another causative mechanism of landslides. Thus, further field study is encouraged to promote slope hazard assessment.

Highlights • Long-term slope instability after major earthquakes was studied by introducing examples in the past. • Compound effects of earthquake and rainfall on slope instability are presented. • Continuous slope instability along major tectonic lines is discussed. • Landslides triggered by abnormal ground water pressure are touched upon. • The concepts of process zone and geopressure should be investigated in more details. • The studied cases suggest the importance of more geological/geomorphological studies for understanding the landslide hazards in tectonically active regions of the world.