3d seismic velocity structure imaging beneath Flores region using local earthquake tomography

Abstract

Abstract Flores is one of the seismically high activity zones of Indonesia region as a consequence of Indo-Australian plate subduction under the Eurasian plate. We investigate 3D seismic velocity structure beneath Flores region and the surrounding area as an effort to understand earthquake source mechanisms and subsurface geometry for the purpose of earthquake disaster mitigation. The study based on travel-time tomography using 223 earthquakes provided by webdc.eu catalog data which is recorded by up to 4 stations during period from January 2010 to March 2018. In the early data processing stages, a total of 1763 P-wave arrivals and 1763 S-wave arrivals were manually picked from 15 seismic stations around the Flores region using SeisGram2k70. 170 events with minumum error in VELEST used to derive a minimum 1D velocity model. The combination of Santosa & Haslinger and AK135 velocity model used as a reference velocity model to Flores region. Futhermore we applied Local Earthquake Tomography (LOTOS 12) to investigated 3D seismic velocity in order to describe anomalous distribution of P and S wave velocities beneath Flores Region. The results showed that Flores region is dominated by a negative seismic velocity anomaly and a high Vp / Vs ratio that is thought to be related to the fault area due to the Flores Thrust Zone in the north and west of Flores and the upward fault in east Flores. The southern part of Flores is dominated by positive anomalies and a low Vp / Vs ratio which is thought to be igneous and metamorphic layers with a low liquid saturation level. Insufficient data causes the resulting tomographic resolution to be poor.