SEISMIC PROPERTIES AND FRACTAL DIMENSION OF SUBDUCTION ZONE IN JAVA AND ITS VICINITY USING DATA FROM 1906 TO 2020

Abstract

As the highest population density area in Indonesia which experienced tsunami-earthquakes in 1921 (Mw7.6), 1994 (Mw7.6), and 2006 (Mw7.7), the Java region has the threat of seismic activities, which could inflict great losses. Several seismic hazard studies have been carried out, but essential parameters have not been explicitly identified, and data on earthquake return periods remain limited. This study addresses such issues by identifying the seismic properties, including the seismic activity (a-value), frequency magnitude distribution related to the tectonic parameter (b-value), fractal dimension (D), and maximum magnitude (M_max) of the subduction zone along the Java Island. The earthquake data used are those from 1906 to 2020. The research started with the processing of earthquake data, continued by determining the a-b values of Gutenberg-Richter relation using the maximum likelihood method. The fractal dimensions were estimated based on the fracture distance and the maximum magnitudes were calculated using some return period scenarios. Our results show that low seismic activity levels are relatively consistent with a low b-value pattern. The lowest b-values are on the south coast of West Java and the south coast of Central-East Java. Based on the fractal dimension analysis, the interplate zones have a more complex fault geometry than intraplate ones. The maximum earthquake magnitude estimation of each subduction segment is presented and discussed comprehensively in this paper. These findings will redound to the benefit of earthquake and tsunami disaster mitigation and earthquake modeling efforts for future seismic hazard studies.