POLARIZATION ANALYSIS AND 3D PATTERNS FOR THE SIX BASIC SEISMIC MOMENT TENSORS

Polarization is an important property of seismic waves that specifies the direction of particle motion. A full polarization measurement system in 3D space could be exploited for passive seismic event detection, seismic direction finding, and wavefield filtering. Seismic sources with different moment tensors will cause polarization differences which could in principle be used for focal mechanism analysis, even for moment tensor inversion. Here, we simulate the 3D vectoral seismic data set for the six basic moment tensor sources which are then used for polarization analysis. Then, we analyze the polarization patterns (azimuth and inclination angle variations) for P and S waves over the ground surface for a buried source, taking into account polarity changes. The results show that the seismic waves from the different basic moment tensor sources have dissimilar polarization characteristics. Such patterns could be exploited to invert for the hypocenter location and the moment tensor of the source. We next consider an actual 3C borehole microseismic field data set and extract the polarization angle. It is clear that a much wider aperture monitoring system is required to sense rapid and/or appreciable angular changes in the polarization vector for effective moment tensor inversion.