An iterative algorithm for separation of S and ScS waves of great earthquakes

Teleseismic SH waves are essential for imaging the rupture processes of large earthquakes. However, for great earthquakes (M8+) such as the 2004 Sumatra earthquake, the 2008 Wenchuan earthquake and the recent Northeastern Japan earthquake, the source duration is very long. Thus the SH waves are overlapped with ScS waves for epicentral distances larger than 60 degrees, leaving contaminated S waves for source processes modeling. Therefore artifacts in finite fault models of large earthquake could be produced with such contaminated body waves. We propose an iterative algorithm based on the slowness information of S and ScS waves and stacking technique, to separate S and ScS waves with records from a regional seismic network. Tests on various data sets of synthetic seismograms show that the algorithm is effective in retrieving SH waveforms from complicated wave trains containing both S and ScS. Separation of waveforms for the 2008 Wenchuan earthquake with our algorithm clearly demonstrates the influence of ScS energy, especially at the later stage of the S wave.