Article,
S-wave identification by polarization filtering and waveform coherence analyses
Bulletin of the Seismological Society of America, 102 (2): 854--861 (Apr 1, 2012)
DOI: 10.1785/0120110140
Abstract
High-resolution imaging with microseismic events requires the use
of large and consistent data sets of seismic phase arrival times.
In particular the S phase is important to derive physical parameters
of the subsurface. Typically this phase is identified on one of the
horizontal seismogram components by a change of signal amplitude
and frequency as compared to the previous P phase. However, reliable
S-phase identification can be difficult for local events because
of a signal overlap with the P coda, the presence of converted phases,
and possible S-wave splitting due to anisotropy. In this study we
propose a new data processing technique aiming at uniquely identifying
the S-phase arrival using all available records from a seismic network.
The technique combines polarization analysis of single three-component
recordings of an event with analysis of lateral waveform coherence
across the network. This makes it possible to construct seismic sections
in which the first arrival is the S phase. This graphical representation
can support an operator in both the analysis of single events and
in semiautomatic analyses of large datasets. In addition, an automated
stacking velocity analysis provides S-wave velocities from these
sections. We demonstrate the applicability of this technique using
synthetic seismograms, and we evaluate the efficacy on a dataset
of three-component velocimeter records from local earthquakes of
the Campania-Lucania Apennines (southern Italy) recorded by the Irpinia
Seismic Network (ISNet).
