HYPOCENTER DETERMINATION USING A NON-LINEAR METHOD IN BALI, LOMBOK AND NUSA TENGGARA REGIONS, INDONESIA: PRELIMINARY RESULT
Fajar Rachmadi Priyambada(1,3), Andri Dian Nugraha(2), Pepen Supendi(3)

1) Master Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institut Teknologi Bandung, Bandung 40132, Indonesia
2) Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung 40132, Indonesia
3) Agency for Meteorology, Climatology, and Geophysics (BMKG), Jakarta 10720, Indonesia

Abstract

Bali, Lombok, and Nusa Tenggara are the region in the south of the Indonesia Archipelago. This region has relatively high seismicity due to subduction activity and faulting. The first step of the tomography study for inferring the geometry structure beneath Bali, Lombok, and Nusa Tenggara is to conduct precise hypocenter location. In this study, we used waveform data from the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG), which the study area is between 112 - 128 E and 4 - 13 S. Our preliminary results, we have re-picked 7967 P-wave and 3254 S-wave arrival times for 933 events in the time period from January to March 2019. The non-linear method was conducted using the oct-tree sampling algorithm from the NonLinLoc program to determine the hypocenters location. We also compared the results with BMKG catalog data. Our results show better clustering earthquakes with RMS error mostly close to zero and represent the geological structure in this region. The results show a shift in the location of the epicenters between 0.1 km to 1000 km, while for the focus depth between 0.006 - 500 km, with the azimuth shift being dominated to the northeast and southwest. The future and ongoing works, we will conduct a tomography study to imaging 3-D seismic velocity models beneath Bali, Lombok, and Nusa Tenggara using the fast marching method.

Keywords: Bali, Lombok, Nusa Tenggara, non-linear method, hypocenter, seismicity

Topic: Earth and Planetary Sciences