Improved Weighting for Focal Mechanism Inversion:Application to the 2013 Lushan Earthquake Data

We discuss weighting in two grid searching methods, cut and paste (CAP) and computer programs in deismology (CPS), to determine source mechanisms from waveform inversion. We found their weightings differs:CAP weighting focuses on the influence from amplitute only; while CPS stresses the difference of SNR for all waveforms. The weighting from the two methods are incompatible, as CAP weighting increases when epicentral distance increases, while CPS weighting decreases. In order to take advantage of these two weighting methods, we combined them and improved the precision of weighting by estimating the amplitute or relative error from the waveform itself. By applying grid search inversion on the 2013 LuShan earthquake data, we show the advantages of our weighing method in a comparison of three experiments based on CPS with different weightings:SNR weighting (CPS), amplitute weighting (CAP) and our improved weighting (CPS & CAP). The preferred source mechanism of LuShan earthquake from our study were strike 211±3°, dip 41±1°, and rake 94±2° and source depth was 17km, and consistent with the mechanisms other researchers have found for stress distribution and geological structure. The case affirms the advantages of our weighting.