Absolute Locations of Earthquakes in Eastern Java Determined by Using One Dimensional P-wave Velocity Model
Ratri Andinisari* (1), Andrean V. H. Simanjuntak (2), Rahadatul A. N. Dhanarsari (1)

(1) Department of Civil Engineering, National Institute of Technology, Malang 65152, Indonesia
(2) Meteorological, Climatological, and Geophysical Agency (BMKG), Jakarta 10720, Indonesia
*) corresponding author: aratri[at]lecturer.itn.ac.id.

Abstract

The island of Java, located in the southeastern subduction zone of Australian plate beneath Eurasian, is a region rich of seismicity. Moderate to large earthquakes with magnitudes of 5.0 to 7.8 have been striking the region, making the study of its seismicity an utmost importance. Unfortunately, seismicity along the eastern part of Java has rarely been studied or assessed. This study serves as preliminary research to bridge the knowledge gap regarding the seismicity of eastern Java by performing two analyses. First, P-wave velocity inversion was performed by using travel times of earthquake data that occurred in eastern Java from January 2008 to February 2022. Then, earthquake relocation was carried out by using the newly derived velocity model. The obtained P-velocity model increasing slowly from 5.39 km/s at the surface down to the depth of ~35 km. A large jump of P-velocity can also be found at the depth of 40 km, where it sharply increases from 7.21 to 7.98 km/s and keeps on increasing up to 8.39 km/s at the depth of 200 km. The resulting absolute locations of earthquakes during the period of our study are mostly concentrated along the offshore area south of East Java. The hypocentral depths vary from the south to the north in accordance with the active subduction zone with the deepest hypocenter reaching ~150 km. The average RMS residual of all the relocated events is 0.40 s with the horizontal and vertical errors of 9.99 and 13.64 km, respectively.

Keywords: seismotectonic, absolute location, velocity model

Topic: Environmental, disaster management and mitigation