ANALISIS GEMPA BUMI SUMATRA BARAT C050294B DI BIDANG SUBDUKSI SUMATRA PADA BERBAGAI STASIUN OBSERVASI ASIA TIMUR
This research analyzes the seismogram of an earthquake C050294B, in West Sumatra to investigate the S speed structure under South-East Asia through seismogram fitting, where the seismogram data is recorded in some East Asia observational stations. The seismogram comparison between the observed and synthetic seismogram is carried out in time domain and three Cartesian components simultaneously. The GEMINI program is used to calculate the synthetic seismogram, where the input is initially the global earth model of PREMAN. A low-pass filter with frequency of corner at 20 mHz is subjected to both seismograms. Very strong deviation is found by seismogram comparison that on the arrival time, oscillation number and is amplitude height, on surface wave of Love and Rayleigh, and body wave S. A correction to the S speed structure is needed, that covers earth crust depth, gradient of speed’s polynomial that a positive for h in upper mantle and values of zero order coefficients for in the upper mantle, and a little change at S speed in earth layers under the upper mantle till the CMB depth to obtain the seismogram fitting. The obtained seismogram fitting is excellent on waveform, as well as the time travel or the oscillation number. The research’s result shows that the South-East Asia zone has a strong negative anomaly of S speed structure in upper mantle. This result differs from other seismological result.
Keywords : Seismogram comparison, negative anomaly, SE Asia
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