Improving Constraints on Centroid Depth from Joint Inversion of Teleseismic Body-Wave and Spectral Amplitude of Rayleigh Waves

Abstract:

Reliable and accurate focal depth of moderate size earthquakes (Mw5.5-Mw7) is important in many aspects of seismological studies, such as mapping the thermal-mechanical fault structure variation and revealing depth-dependent plate tectonics process. Identification of teleseismic depth phase (e.g. pP and sP) is usually performed to determine focal depth. However, as for shallow events, a relatively long source rupture duration may cause waveform interference to picking of depth phase. Fortunately, both long period teleseismic body-wave and Rayleigh wave spectral amplitude are sensitive to variation of centroid depth. In order to combine depth phase signals in teleseismic body-wave and broadband frequency information in Rayleigh wave’s spectral amplitude, we propose a new joint inversion method performed using grid search for centroid depth. Because of the increased global coverage of seismometer networks and relatively high signal-to-noise ratio of teleseismic recording, firstly, focal mechanism is determined based on Cut-and-Paste method of teleseismic body-wave. Then an optimal centroid depth is inverted to best fit observed teleseismic body-wave and regional Rayleigh wave spectral amplitude. Application of this joint method to several well studied moderate size earthquakes verify not only robustness of the method, but also quantitatively improved accuracy of estimates of centroid depth.