Investigating the S Wave Velocity Structure Beneath Southwest North America through Seismogram Comparison of C052297B Earthquake

In this research the investigation concerning the earth structure beneath the Southwest North America landmass is carried out, which covers a small area, i.e. between Mexico and California. S speed models for this area are obtained by carrying out seismogram fitting in time domain and three simultaneous Cartesian components. Seismogram data are the effect of earthquake C052297B in Guererro, Mexico, and seismogram fitting between observation and synthetic at the stations of the property of seismic network TS. Synthetic seismogram is calculated using the GEMINI program, where the initial input is earth model IASPEI91 (iasp) and PREMAN. To both real and synthetic seismograms a low-pass filter with the frequency corner at 20 mHz is imposed. Results of waveform analysis show the very unsystematic and strong deviation, which are observed from the waveform comparison, where the deviations cover waveform, arrival time, oscillation's amount and amplitude height. Such discrepancies are met on S wave, Love and Rayleigh surface wave, and ScS wave, where the stations epicentral distances are below 30. With this method we can see how sensitive the waveform to structure of earth layer is. To accomplish the discrepancies a correction to the earth structure is needed, which covers the earth crust thickness, speed gradient of h and coefficient for the h and v in upper mantle for the fitting at surface wave, and a little change of S speed structure at layer under upper mantle as deep as 771 km for the waveform fitting of S wave, and a little change at base mantle layers, for the fitting of ScS wave. At some stations, fitting of P wave is also achieved by means of correction at S speed