ANALYZING THE SEISMOGRAM OF EARTHQUAKES ON SUMATRA-JAVA SUBDUCTION PLANE AT CHTO OBSERVATION STATION

Bagus Jaya Santosa

Abstract


This research analyzes the earthquakes in subduction plane of Sumatra-Java to investigate the S speed structure under
South-East Asia through seismogram fitting, where the seismogram data is recorded in CHTO observational station,
Thailand. The observed seismogram is compared to synthetic seismogram in time domain and three Cartesian
components simultaneously. The synthetic seismogram is calculated with GEMINI program, where the input is initially
the global earth model of SPREM. Both seismograms are subjected to a low-pass filter with frequency of corner at 20
mHz. Seismogram comparison shows very strong deviation by observing the arrival time, oscillation number and is
amplitude height, on surface wave of Love and Rayleigh, and S body wave. Therefore a correction to the S speed
structure is needed. Corrections cover earth crust depth, gradient of speed’s polynomial that a negative 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. 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 between Sumatra Island and
Thailand 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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