Two comparable earthquakes produced greatly different coseismic landslides: The 2015 Gorkha, Nepal and 2008 Wenchuan, China events

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 m(2)) over a similar to 35 600 km(2) region with a volume of (444-584)x10(6) (average 509x10(6)) m(3) and total area of 44.78x10(6) m(2). In contrast, the Wenchuan Earthquake triggered 25 580 large landslides over a region of similar to 44 000 km(2) with a volume of (7 128-9 479)x10(6) (average 8 219x10(6)) m(3) and a total area of about 670.65x10(6) m(2). 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.