Use of the PP phase to study the earthquake source

Abstract

The space‐time history of the rupture process of a large earthquake can be determined from directivity analysis of source time functions deconvolved from long‐period P waves. However, such analysis requires a good azimuthal distribution of stations, which is often difficult to obtain. We have developed a method for deconvolution of long‐period PP waves which is useful for a distance range of 70° ‐ 123° and 145° ‐ 165°, thus increasing both the available data and the ray parameter aperture. The PP waveform is Hilbert transformed to remove the effect of the PP caustic and then deconvolved in the time domain. We have tested the method on the 2 July 1974 Kermadec event (Ms=7.2) and obtained nearly identical source time functions from P and PP waves.