NH43D-01
Geological, Geophysical, and Stochastic Factors in Nepal’s Gorkha Earthquake-Triggered Landslide Distribution

Thursday, 17 December 2015: 13:40
309 (Moscone South)
Jeffrey S Kargel1, Daniel H Shugar2, Umesh K Haritashya3, Gregory J Leonard1, Eric Jameson Fielding4, Kenneth W Hudnut5, Randall Jibson6 and Brian D Collins7, (1)University of Arizona, Tucson, AZ, United States, (2)University of Washington Tacoma Campus, Tacoma, WA, United States, (3)University of Dayton, Dayton, OH, United States, (4)Jet Propulsion Lab Caltech, Pasadena, CA, United States, (5)USGS Pasadena Field Office, Pasadena, CA, United States, (6)U.S. Geological Survey, Golden, CO, United States, (7)USGS Western Regional Offices Menlo Park, Menlo Park, CA, United States
Abstract:
On 25 April 2015, a magnitude 7.8 earthquake struck Nepal. Subsequently many large aftershocks shook the region, including one of magnitude 7.3. Much damage and over 4300 landslides were triggered. The landslides were mapped by a volunteer group who self organized to undertake an emergency response to the earthquake disaster. The number of landslides is fewer than expected based on total released seismic energy. This may be because of lack of a surface rupture and possibly also because of high surface-wave attenuation due to rugged surface topography or to the geological and geophysical characteristics of the upper crust. The observed landslides were primarily in the southern half of the Himalaya in areas where the steepest slopes occur and where peak ground accelerations were relatively high. The landslides are also concentrated on the tectonically downdropped block. However, the distribution is complex and varies dramatically from valley to valley. Furthermore, different types of landslides are concentrated in different geologic materials, which suggests local factors control the valley-scale attenuation or amplification of seismic waves or the way wave disturbances couple to the local geologic materials. Across the earthquake-affected zone on the regional scale, wave attenuation and also net downdrop and uplift may also explain as much about the distribution of landslides as slopes and distance from large slips on the fault. We will offer the regional distribution results and some specific case studies to illustrate a set of possible controlling factors.