PENERAPAN TOMOGRAPHY GELOMBANG RAYLEIGH UNTUK MENENTUKAN STRUKTUR SEISMIK LAPISAN MANTEL ATAS DI KEPULAUAN INDONESIA

Abstract

ABSTRACT

The seismic structure of upper-mantle beneath Indonesia is investigated using seismograms recorded by National and Global seismographic stations around Indonesia. To determine the Rayleigh waves phase dispersion, the two-stage multimode surface wave tomography incorporating finite-frequency effects is employed to analyze vertical- component seismograms. Data were used 560 events with moment magnitude 6,0 and greater occurred between January 1995 and December 2008. The data were obtained from 23 national seismic networks operated by BMKG Indonesia and 53 global seismic networks operated by IRIS/FARM. In the first step of the study, the path-average dispersion curves along the great circle for each event are determined using automatic multi-mode phase speed measurements. In the second step, Rayleigh-wave phase speed maps of the entire region of Indonesia were obtained as a function of frequency multi-mode incorporating finite frequency effects. The phase speed models were constructed in a period, range from 30 to

160 sec. The phase speed maps of the fundamental mode displays remarkable consistency across the Indonesian region for all periods. The two most prominent features are high velocities (+2 to +6%) beneath the active Indo-Australian plate and slower velocities (-2 to -6%) beneath the Sunda shelf and Banda Sea.

Keywords: Upper Mantle; Rayleigh Waves; Tomography; Waveform; Indonesia