POLA TEKTONIK ZONA TRANSISI BUSUR SUNDA-BANDA BERDASARKAN TOMOGRAFI DOUBLE DIFFERENCE

Abstract

The area in the south of Flores island where the Australian continental crust moves towards the trench is a transitional zone from the Sunda Arc to the Banda Arc which is a transition zone from subduction to continental arc incision. This area has a high level of seismicity which causes a large magnitude earthquake to a tsunami that has an impact on fatal damage to the surrounding area so further studies with a better resolution are needed to identify a model of the tectonic system that is developing in this area. The Double Difference tomography method is used to analyze the velocity structure and explain the tectonic conditions in the zone, especially subduction and active volcanoes in this zone. In this study, data were obtained from a seiscomp3 BMKG with a research area boundary of 116o to 125o east longitude and -6.5o to 12.5o south latitude, used the arrival time phase of P and S waves from 15 stations spread across the research area, with a data period of January 2015 to December 2019 obtained 3140 event data. The results of the hypocenter relocation show a pattern that can be interpreted and related to the tectonic pattern in this zone, the fix dept is reduced with the distribution of residual values that is more accumulated at zero, making it easier to interpret and interpret the seismogenic features in the Sunda-Banda arc transition zone, indicating that this earthquake was caused by The subduction zone (Megathrust) is in the south, the back-arc thrust in the north and there are also disturbances from local faults and volcanic activity. From the tomography results, the Vp, Vs tomograms and the Vp / Vs ratio obtained from the division, can explain several important structures in this area, especially for depths of up to 250 km. The subduction of the oceanic lithosphere associated with the convergence of Australia and Sundaland is well imaged with high P wave velocities, quite firmly up to a depth of 250 km as well as the results shown from the S wave velocity whereas, from the Vp / Vs ratio, much lower values are obtained in this section. The area around the Savu Sea, this provides information regarding the accumulation of sediment in the Savu Sea area and the possibility of partial melting. The low-velocity zone is probably associated with the partial melting zone and active volcanoes in this area.