The Role of the 2008 Mw 7.9 Wenchuan Earthquake in Topographic Evolution: Seismically Induced Landslides and the Associated Isostatic Response

Abstract

The widely held notion about the relationship between reverse-faulting earthquakes and mountain building has been challenged by recent studies suggesting a net coseismic lowering of surface height due to the 2008 Mw 7.9 Wenchuan earthquake. We calculate the long-term isostatic response to the removal of coseismic landslide mass produced by the 2008 Wenchuan earthquake, using re-estimated coseismic landslide volumes. The total isostatic response volume is associated with the input landslide volumes and ranges from ~1.0 to 2.7 km3, which did not change much with the varied input value of the effective elastic thickness (Te); however, the rebound distribution changes with Te. Consequently, the net uplift volume will be ~1.2–2.9 km3, taking into account the total landslide volume of 2.8 + 0.9/−0.7 km3 and the coseismic uplift of 2.6 ± 1.2 km3. The isostatic response due to Wenchuan earthquake is ~0.3 m but may vary from 0.15 to 0.6 m (input minimum and maximum landslide volumes from the combined scaling parameters, respectively) in the central Longmen Shan. We also find that the average net uplift is ~0.11–0.26 m, which resulted from the imbalance between earthquake-caused uplift and the isostasy within the landslide region due to the Wenchuan earthquake. The total isostasy could reach ~550–1,300 m during the past 10–15 Ma, in the corridor bounding the coseismic surface ruptures. Our findings reveal that the evolution of local topography in the Longmen Shan region is inevitably related to the repeated tectonic events, especially the strong earthquakes similar to the 2008 Wenchuan earthquake.