Epicenter and Hypocenter Determination Using the Grid Search Method for the 5 August 2018 Lombok Earthquake

Abstract

The Lombok Island region is characterized by complex tectonic interactions associated with the subduction of the Indo-Australian Plate beneath the Sunda Plate and the activity of th Flores Back Arc Thrust, resulting in frequent moderate to large earthquakes. One of the most significant events in this region is the Mw 7.0 Lombok earthquake that occurred on 5 August 2018. Accurate determination of the earthquake epicenter and hypocenter is essential for understanding the source characteristics and regional seismotectonic setting. Grid search method was applied to determine the epicenter and hypocenter of the 5 August 2018 Lombok earthquake using P-wave arrival time data revorded by 15 accelerometer. The method evaluates a 3D spatial grid by calculating thereotical travel times based on a homogeneous P-wave velocity model and minimizing the MRS residual between observed and calculated arrivals, yielding a best fit location at latitude −8.2483°, longitude 116.5566°, focal depth of 39.00 km, and a minimum RMS of 1.0064 . Comparison with the BMKG earthquake catalog shows good agreement in apicenter location and focal depth, while RMS based analyses indicate that the earthquake location is well constrained both horizontally and vertically.