Document Type : Seismology and Engineering Seismology
Geophysics Dept., FMIPA, ITS, Jl. Arif Rahman Hakim 1
This research investigated the S wave velocity structure below SE Asia, by analyzing the seismograms of South Sumatra earthquakes at CHTO, QIZ, KMI, ENH and SSE stations, in the time domain and three Cartesian components simultaneously. The main data is waveform comparison between the measured seismogram and synthetic one, instead of travel time or indirect data from dispersion curve, as other seismological researches. The synthetic seismogram constructed from anisotropic PREM global earth model deviates greatly from the measured one, from surface wave to multiple core reflected waves. Corrections cover the gradient change of bh in the upper mantle layers, which turns from negative into positive, as stated in the anisotropic PREM, changes of earth crust depth and zero order coefficients of b velocity function in all earth mantle layers. So the fitting is obtained on the arrival time, the Love and Rayleigh surface wave, the S, and the repetitive core reflected ScS, ScS2 and ScS3 waves. This result reveals that South East Asia, being stretched due to tectonic release, has a mantle part with negative anomaly on S wave velocity and vertical anisotropy in all earth mantle layers. Error in CMT solution is shown by distinct amplitude differences in the surface waves.