Investigating S velocity structure of the upper mantle beneath west Indonesia using seismogram analysis of two strong south java earthquakes in Malaysian seismological network

摘要

This research investigated the S speed structure in the upper mantle beneath West Indonesia by analyzing the seismogram triggered by the C052606A and C071706B earthquakes in South Java and recorded at the Malaysian seismological network MY. The method used is waveform comparison between the measured seismogram and the synthetic one in the time domain and three Cartesian components simultaneously, instead of travel time data or dispersion curve, which are commonly used by other seismologists. The seismogram comparison was conducted in the same unit and a low-pass filter with 20 mHz corner frequency was applied to both seismograms. Seismogram analysis shows very strong deviations in the arrival times and amplitudes of the Love and Rayleigh surface waveforms. To solve the observed deviation, a correction on the earth structure covering the speed gradient of β_h and the value of zero-order coefficients for the β_h and β_v in the earth upper mantle is required. The research's result shows that the area of East Sumatra and Borneo has negative correction of S speed structure in the upper mantle layers, compared to PREMAN standard earth model. This result is different from other seismological result.