W-Phase Inversion for Finite Fault Slip

The W-phase is a long-period seismic wave arriving together with the P wave, whose high group velocity makes it particularly useful for rapid determination of source mechanism. To date inversions of W-phase waveforms have used the point source approximation. In this study we consider the utility of the W-phase for extracting information about the finite character of faulting in major earthquakes. We have applied W-phase inversion to seismic waveforms recorded following the 2010 Chilean earthquake (Mw=8.8). We consider inversion of broadband waveforms recorded by 21 stations in the distance range 5-90 degrees. The inversion procedure we use largely follows the method described in detail by Kanamory and Rivera (2008). Instead of inverting for the faulting mechanism as has been done in previous work using the W-phase, we assume a faulting geometry of the Chilean megathrust: strike=16, dip=14, and have assumed a rake of 90 degrees. Our preliminary results appear to be compatible with the finite fault solution of Lay et al. (2010). References: Kanamori, H., and Rivera, L. (2008). Geophys. J. Int., 175, 222-238. Lay, T., Ammon, C. J., Kanamori, H., Koper, K. D., Sufri, O., Hutko, A. R. (2010). Geophys. Res. Lett., 37, L13301.