Tio Azhar Prakoso Setiadi, Anne Meylani Magdalena Sirait, Yehezkiel Halauwet, Andrean Vesalius Hasiholan Simanjuntak, Adi Susilo
The 2020 Jepara earthquake (Mw 6.7) represents a significant deep-focus seismic event within the subducting Indo-Australian Plate beneath Java Island. This study investigates its characteristics using automatic moment tensor inversion and double-difference relocation based on seismic data from the Meteorology, Climatology, and Geophysics Agency (BMKG). A total of 1,899 earthquakes recorded between 2010 and 2022 were analyzed, focusing on events with a depth of up to 600 km. Moment tensor analysis revealed a normal faulting mechanism with two nodal planes: the first with a strike of 310º, dip of 59º, and rake of -68º, and the second with a strike of 92º, dip of 37º, and rake of -121º. The centroid depth was refined to 544 km, and the variance reduction (VR) exceeded 60%, which classifies the results as high-quality (Category A). Approximately 85% of the hypocenters were successfully relocated, improving root mean square (RMS) travel times to less than 1 second. The earthquake is associated with slab dehydration and the polymorphic phase transition of olivine to spinel under high pressure and temperature. These processes contribute to changes in fault mechanisms and the structural variation of the mantle transition zone. The findings enhance understanding of the deep-focus earthquakes beneath Java and can significantly contribute to future earthquake mitigation in Indonesia. © 2025 Faculty of Mining, Geology and Petroleum Engineering University of Zagreb. All rights reserved.
National Research and Innovation Agency, Bogor, 16911, Indonesia; Geophysics Program, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, 16424, Indonesia; Meteorological, Climatological, and Geophysical Agency (BMKG), Central Jakarta, Kemayoran, 10610, Indonesia; Tsunami Disaster and Mitigation Research Center (TDMRC), University of Syiah Kuala, Banda Aceh, 231111, Indonesia; Department of Physic, Faculty of Mathematics and Natural Sciences, Brawijaya University, Malang, 65145, Indonesia; Research Study of Geosciences and Hazard Mitigation, Universitas Brawijaya, Malang, 65145, Indonesia
