Spatial variation of b-values correlation with tectonic activity along the Southern Java subduction zone

The subduction zone along southern Java Island is part of convergence between the Eurasian and Australian plate which is classified as the active tectonic region in Indonesia. This study brought to determine the seismicity parameters of the southern Java subduction zone based on the earthquake event catalog from 1970 until 2020. The spatial variation of the b-value is used as the basic analysis that employs statistics on the earthquake event catalog to identify the seismicity index and its relationship with the geological structure and tectonic activity. The study region lies within 7-12°S 105-115°E and the catalog data was acquired from the National Earthquake Information Center (NEIC) with various magnitude types. The mapping of b-value spatial distribution is calculated using each hypocenter as a grid point for which all events in its neighborhood are taken to determine the corresponding b-value. The results show that several spots along the subduction zone have a high b-value, especially in the south of West Java, and a low b-value is observed in East Java. This variation correlates with the different tectonic settings because of high deformation rate and fracture from the large fault releasing the stress from the subduction activity. The area with a low b-value could be prone to a destructive and massive earthquake with high magnitudes in the future.