cognizancejournal.com Firman Pratama Putra et al, Cognizance Journal of Multidisciplinary Studies, Vol.3, Issue.11, November 2023, pg. 226-235 (An Open Accessible, Multidisciplinary, Fully Refereed and Peer Reviewed Journal) ISSN: 0976-7797 Impact Factor: 4.843 Index Copernicus Value (ICV) = 77.57 ©2023, Cognizance Journal, cognizancejournal.com, All Rights Reserved 226 COMPARISON OF EARTHQUAKE HYPOCENTER RELOCATION METHODS IN THE JAVA REGION, INDONESIA Firman Pratama Putra 1 ; Udi Harmoko 2 ; Gatot Yuliyanto 3 1,2,3 Physics Departement, Diponegoro University, Jl. Prof. Soedarto, SH, Semarang, Indonesia – 50275 2 udiharmoko@gmail.com DOI: 10.47760/cognizance.2023.v03i11.015 Abstract— Java is a frequent island of earthquakes caused by the subduction of the Indo-Australian plate under the Eurasian plate. The mitigation of earthquake disasters is by relocating the hypocenter. Hypocenter relocation was conducted in order to obtain a more accurate earthquake position, which can be used to interpret the structure under the earth's surface. The Modified Joint Hypocenter Determination (MJHD) and Double Difference (DD) methods are required when applying earthquake hypocenter relocation. The objective of research is comparing the relocation results in the Java region with the Modified Joint Hypocenter Determination (MJHD) and Double Difference (DD) Methods for obtaining the distribution of earthquake hypocenters before and after relocation. The study has obtained arrival time data in the form of BMKG catalog data from the period of January 1, 2022 through May 30, 2022 in the Java area with the coordinates of 6.0 LS - 12.0 LS and 106.0 BT - 114.0 BT. The MJHD method compares the travel time difference of a set of data that occurs simultaneously in order to obtain a more accurate hypocenter position, while the DD method compares the hypocenter distance of the two earthquakes with the station distance, so that Ray Path and Waveform are considered equal. The relocation of the initial earthquake has a depth of 10 km, resulting in a shift of shallow earthquakes clustered in the active fault section, while deep earthquakes are clustered in the subduction zone section. The results of relocation with the MJHD method obtained 637 earthquakes. Keywords— mitigation, MJHD, Double Difference (DD), waveform, Arrival time INTRODUCTION Hypocenter relocation is a way to recalculate the hypocenter point of an earthquake to obtain an accurate position. Hypocenter relocation is carried out to see the lineation of the earthquake's hypocenter in order to represent the fault structure below the earth's surface [7]. The Java region is an island that frequently experiences earthquakes, this is caused by activity in the subduction zone between the Indo-Australian plate which is subducting into the Eurasian plate, so that it can form an ocean trench in the region [4]. In general, the Java region is divided into three structural pattern directions, namely the northeast to southwest direction which is called the Meratus pattern, the north to south direction which is called the Sunda pattern and the east to west direction which is called the Javanese pattern [12]. An earthquake is a sudden shift in the structure of rocks in the earth's crust caused by the shifting of tectonic plates [6]. To provide accurate earthquake information, there are several factors, including the magnitude of the seismic waves recorded by the earthquake recording station, the reading of the wave arrival time, and the velocity structure of the seismic waves [10]. To obtain more accurate hypocenter relocation results, research is needed using the Modified Joint Hypocenter Determination (MJHD) method developed by Hurukawa and Imoto in 1990. The Double Difference (DD) method was developed by Felix Waldhauser and Ellsworth in 2000. The aim of this research is to compare relocation results in the form of distribution maps, cross sections and residual histograms in the Java region using the Modified Joint Hypocenter Determination (MJHD) and Double Difference (DD) methods to obtain seismic distribution results before and after relocation. LITERATURE REVIEW A. Hypocenter Relocation Hypocenter relocation is a process of re-determining the hypocenter point of an earthquake to obtain a more accurate position. There are several factors that can increase the accuracy of relocation results, namely