Rapid slip-deficit rates at the eastern margin of the Tibetan Plateau prior to the 2008 M w 7.9 Wenchuan earthquake

Abstract

The Longmen Shan is the steepest topographic front at the India-Asia collision zone and the site of the Mw 7.9 Wenchuan earthquake. Here to explain the interseismic GPS velocities across the greater Longmen Shan region, we develop a boundary element model including earthquake cycle effects, topography, the westward dipping Beichuan Fault and a ∼20 km deep, shallowly dipping, detachment, inferred from observed afterslip and from structural considerations. Previous analyses which neglected the detachment and earthquake cycle effects have found shortening rates near zero. In contrast, we find that interseismic GPS data are consistent with a shortening rate of 5.7±1.5mm/yr and maximum surface slip-deficit rate of 9.5±2.5mm/yr. This model unifies the interpretation of geodetic deformation throughout the earthquake cycle and suggests that the Longmen Shan is an active fold-and-thrust belt with of Wenchuan-like recurrence intervals as short as 600 years.