S WAVE VELOCITY STRUCTURE IN NONTECTONIC SE ASIA BY SEISMOGRAM ANALYSIS OF THE EARTHQUAKES IN SUMATRA–JAVA AT TATO STATION, TAIWAN

The S wave velocity structure beneath South-East Asia and South China Sea due to earthquakes in Sumatra–Java subduction zone has been investigated through seismogram analysis in time domain and three components simultaneously, using data recorded in TATO, Taiwan seismological station. The synthetic seismogram was calculated using the GEMINI method, which consists of the earth model and the CMT solution of the earthquake. A low-pass filter with corner frequency of 20 mHz is imposed to the seismograms. Response file inversion subjected on the measured seismogram will compare the measured and the synthetic seismogram in the same unit. The seismogram comparison indicated that the synthetic seismogram constructed from PREMAN earth model deviates greatly from the measured one. The deviation occurred on the arrival time of surface wave of Rayleigh and Love as well as S body waves. The S, Love, and Rayleigh waveform deviations on arrival time or oscillation number are solved by changing the gradient of βh into positive in the upper mantle layers, and corrections for zero-order coefficients of β speed polynomial in every earth mantle layers. The interpretation results of seismogram analysis using waveform comparison indicate that the nontectonic South-East Asia area in front of subduction zone has strong negative correction of βv in the upper mantle and with smaller factor also at earth layers below. This result shows stronger vertical anisotropy than that indicated by the PREMAN earth model.