ENHANCED GPS INVERSION TECHNIQUE APPLIED TO THE SUMATRA 2004 EARTHQUAKE AND TSUNAMI

Since the devastating earthquake and tsunami in 2004 offshore Sumatra, many source models have been put forward, based on different inversion techniques. Recent studies clearly show that the modern GPS-measurements in near real time can achieve high resolving power for slip, which is crucial for determining tsunami initial conditions especially in the near field. However, most of the GPS-based inversions rely on assumptions on fault geometry which are not satisfactory for different reasons. We propose a method to accurately represent the subduction zone geometry and impose boundary conditions that overcome the problems associated with the use of global moment minimization in the inversion process. Using this method we address the widely discussed issue of the effect of postseismic slip which is often invoked to explain the discrepancy between the results of inversion of far field permanent station data and near field campaign or coral-head data for the 2004 event. We show that by using an appropriate earth model this discrepancy can be reduced significantly. Inverted source models for the 2004 event including a version with splay faulting using rupture timing derived from quasi-real-time GPS data are used as input for a tsunami wave propagation model and compared to JASON satellite radar altimetry data.