Determination of earthquake focal depths and source time functions in central Asia using teleseismic P waveforms
We developed a new method to determine earthquake source time functions and focal depths. It uses theoretical Green's function and a time-domain deconvolution with positivity constraint to estimate the source time function from the teleseismic P waveforms. The earthquake focal depth is also determined in the process by using the time separations of the direct P and depth phases. We applied this method to 606 earthquakes between 1990 and 2005 in Central Asia. The results show that the Centroid Moment Tensor solutions, which are routinely computed for earthquake larger than M5.0 globally using very long period body and surface waves, systematically over-estimated the source depths and durations, especially for shallow events. Away from the subduction zone, most of the 606 earthquakes occurred within the top 20 km of crust. This shallow distribution of earthquakes suggests a high geotherm and a weak ductile lower crust in the region.
Additional Information© 2009 American Geophysical Union. Received 5 June 2009; accepted 7 August 2009; published 12 September 2009. We are grateful to Alex Hutko and another GRL reviewer for their constructive comments that helped us to improve the manuscript. All waveform data used in this study were obtained from IRIS Data Management Center. This material is based upon work supported by the NSF under grant EAR-0439992. Risheng Chu was also partially supported by NSF grant EAR-0337491. This is contribution 10025 of the Caltech Seismological Laboratory.
Published - Chu2009p5972Geophys_Res_Lett.pdf