Mass wasting triggered by the 2008 Wenchuan earthquake greater than orogenic growth
Résumé
Shallow earthquakes are the primary driver of rock uplift in mountain ranges. However, large shallow earthquakes also trigger widespread, coseismic landslides that cause significant but spatially heterogeneous erosion. The interplay between rock uplift and the distribution and magnitudes of coseismic landslides thus raises a fundamental question as to whether large earthquakes and their associated landslides create or destroy mountainous topography. The 2008 Mw 7.9 Wenchuan earthquake in Sichuan, China triggered more than 56,000 landslides, with a spatial distribution that was only partly related to the pattern of tectonic deformation. Here we examine the potential changes in orogen volume using landslide area-volume scaling relationships applied to highresolution satellite imagery. We estimate that coseismic landsliding produced 5-15 km3 of erodible material, greater than the net volume of 2.6 1.2 km3 added to the orogen by coseismic rock uplift. This discrepancy indicates that, even if only a fraction of the landslide debris is removed from the orogen over the likely 2000-4000 yr earthquake return period, the Wenchuan earthquake will lead to a net material deficit in the Longmen Shan. Our result challenges the widely held notion that large dip-slip or oblique-slip earthquakes build mountainous topography, and invites more careful consideration of the relationships between coseismic slip, mass wasting and relief generation.