On the evolution of seismogenic faults in the Longmen Shan, eastern Tibet

A fundamental debate exists regarding the geometry and depth extent of seismogenic faults in eastern Tibet. Along the Longmen Shan, geologic and seismic reflection data reveal a belt of low to moderate angle thrust faults, some of which may have been activated in devastating earthquakes in 2008 (Mw ~7.9, Wenchuan) and 2013 (Mw ~6.6, Lushan). However, geologic and geodetic constraints on these ruptures suggest rupture along relatively high-angle listric reverse faults. Here, we use a combination of focal mechanisms determined from 276 aftershocks (Ms > 4.0) with well-determined waveforms and aftershock distributions from the 2008 event to determine subsurface fault geometry. Our results imply that seismogenic slip occurred along relatively high-angle structures that cross-cut low-angle imbricate faults imaged in reflection seismic data. Thus, we suggest that current geometric models of seismogenic faults may not fully represent the distribution of subsurface seismic hazard along the heavily-populated Sichuan Basin.