Gradiometry for polarized seismic waves

摘要

Wave gradiometry for a generic point source wave model in cylindrical coordinates is developed to utilize the horizontal components of seismic wavefields. Attributes of P-SV and SH waves such as horizontal slowness and its change, the change in geometrical spreading, the change in radiation pattern, azimuth of propagation, and wave polarization can be determined by measuring the horizontal strains and rotations of the wavefield along with three components of displacement. Gradiometer cells composed of an array of three-component seismographs can be used to provide estimates of the wave gradients. Alternatively, a single three-component seismograph collocated with an areal strainmeter (for P-SV waves) or a rotation sensor (for SH waves) can be used to estimate wave polarization and the slowness/amplitude behavior of one aspect of the wavefield. Wave gradients are computed for the 1 April 2007 Solomon Island earthquake using data from the ANZA Seismic Network in southern California and show excellent consistency among stations of the network. Azimuth and slowness of various long-period teleseismic waves are recovered using gradiometry analysis. The consistency of strains computed from the broadband array suggests that they may be used to calibrate Plate Boundary Observatory tensor strainmeters in the region.