Abstract
The 2015 Gorkha Earthquake in Nepal and the 2008 Wenchuan Earthquake in China occurred at the south and southeast margins of the Tibetan Plateau, respectively. Both earthquakes had similar magnitudes of Mw 7.8 and 7.9, caused catastrophic loss of life and damage to property, and generated tens of thousands of landslides. Comparisons of pre- and post-quake satellite images supported by field investigations show that the Gorkha Earthquake triggered at least 2 064 large landslides (defined as covering an area ≥10 000 m2) over a ∼35 600 km2 region with a volume of (444–584)×106 (average 509×106) m3 and total area of 44.78×106 m2. In contrast, the Wenchuan Earthquake triggered 25 580 large landslides over a region of ∼44 000 km2 with a volume of (7 128–9 479)×106 (average 8 219×106) m3 and a total area of about 670.65×106 m2. Several controlling factors including topographic relief, slope steepness, and regional peak ground acceleration (PGA) were investigated to try to explain the great differences between the number, volume and area of the coseismic landslides associated with the two similar earthquakes. We found that the differences primarily arose from an unexpected factor, the dip angle of the seismogenic fault. This discovery should aid understanding the failure mechanisms of quake-triggered landslides, and suggests that more factors should be taken into consideration in estimating coseismic landslide volumes from earthquake magnitudes.
Highlights
The April 25, 2015 Gorkha, Nepal Mw 7.8 and May 12, 2008 Wenchuan, China Mw 7.9 earthquakes have received much attention because both were humanitarian disasters that generated large numbers of coseismic landslides and serious damage (Yin and Liu, 2016)
3 CONCLUSIONS The 2008 Wenchuan and 2015 Gorkha earthquakes have comparable magnitudes, both occurred on the margins of the Tibetan Plateau, and both are characterized by high topography and steep slopes
These similarities might suggest that the number of landslides triggered by these two events would be comparable but the Gorkha Earthquake triggered only 2 064 large landslides (≥10 000 m2), with a total area of 44.78×106 m2 and volume of (444–584)×106 m3, whereas the Wenchuan Earthquake generated 25 580 large landslides that cover 670.65×106 m2 and have a total volume of (7 128–9 479)×106 m3
Summary
The April 25, 2015 Gorkha, Nepal Mw 7.8 and May 12, 2008 Wenchuan, China Mw 7.9 earthquakes have received much attention because both were humanitarian disasters that generated large numbers of coseismic landslides and serious damage (Yin and Liu, 2016). We compiled a polygon-based inventory of large landslides triggered by the Gorkha event, and compared the result to the Wenchuan inventory. We have analyzed and compared correlations between the large coseismic landslides (area ≥10 000 m2) for the two earthquakes with several other relevant factors, such as topographic relief, slope steepness, and PGA. We suggest that the disparate dip angles of the seismogenic faults and the resultant differences in the internal rock deformation were the primary reason for the difference Understanding this factor should improve understanding of coseismic landslide generation mechanisms and help mitigate their associated hazards
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