Analisis Seismisitas Bersadarkan Nilai B-Value: Studi Kasus Gempa Bumi Wilayah Tapal Kuda Jawa Timur, Tahun 2000-2024

Abstract

The Tapal Kuda region in East Java is an area of high seismic activity driven by the subduction interaction between the Indo-Australian and Eurasian plates and the presence of active faults; consequently, it faces a relatively high level of earthquake hazard, necessitating an analysis of seismicity characteristics to support disaster mitigation efforts. This study aims to analyze earthquake magnitude and frequency characteristics, as well as earthquake hazard levels, based on the spatial distribution of b-values in the Tapal Kuda region from 2000 to 2024 using the Maximum Likelihood Estimation (MLE) method. Secondary data from the United States Geological Survey (USGS) earthquake catalog (2000–2024)—comprising event times, epicenter coordinates, depths, and magnitudes—were utilized. Data processing was conducted using MATLAB software with the ZMAP tool to determine the Magnitude of Completeness (Mc), construct the Frequency-Magnitude Distribution (FMD), calculate b-values via the MLE method, and map the spatial distribution of b-values across different depth ranges. The results indicate an Mc value of 4.30 and an overall b-value of 1.08 ± 0.06. At depths of 0–60 km, b-values ranged from 0.6 to 2.0, with values predominantly between 0.8 and 1.2; at depths of 60–150 km and 151–212 km, values ranged from 1.1 to 1.7, with a predominance of 1.1–1.3. Zones with relatively high b-values were concentrated in the central to southern parts of the study area, indicating a prevalence of low-magnitude earthquakes, higher rock heterogeneity, and the influence of volcanic activity; conversely, areas with low b-values exhibited conditions of relatively higher tectonic stress, suggesting a potential for generating larger-magnitude earthquakes. In general, the spatial variation of b-values indicates that seismicity characteristics in the Tapal Kuda region are influenced by the interplay of subduction processes, plate deformation, and local geological conditions.