Measuring PmP travel times using teleseismic S-wave waveform data

Joint inversion for crustal velocity structure using only surface wave dispersion and receiver function data often suffers the non-unique solution problem due to lack of P wave velocity constraint in the data. Here we developed a method for measuring PmP travel time using teleseismic S wave waveform. The major improvement by this method over the previous one-layer-crust search method is its use of a more realistic multi-layer-crust (MLC) velocity model in the study region based on available information. Numerical tests show that compared with the previous search method the MLC search method is faster and more reliable and accurate. One limit of the MLC search method is the requirement of a multi-layer background model, thus this method might not be applicable in regions where the velocity structure is unknown. Nevertheless, our numerical tests show that the MLC search method is robust in the sense that small deviations of the background model from the true velocity model do not influence the results severely. We applied the MLC search method to data from a temporary linear array across the Wabash Valley Seismic Zone in the central USA. We obtained 157 PmP travel-time measurements that show lateral crustal structure variation in the region. The measurements provide additional constraints in joint inversion for crustal velocity structure in this seismically active region.