The Current State of Earthquake Potential on Java']Java Island, Indonesia

Between 2006 and 2020, earthquakes and other geohazards on volcano-dotted Java Island have caused about 7000 deaths, and another 1.8 million people were injured, displaced, or left homeless. In this study, we quantify the current state of earthquake hazard for 29 cities of Java, using seismicity statistics of a cumulative number of small events (natural times) between pairs of large earthquakes. This approach, known as earthquake nowcasting (Rundle et al., 2016), rests on the key concepts of elastic rebound and ergodic dynamics in earthquake fault networks. Our analysis of statistical inference shows that the estimated earthquake potential score (EPS) as on February 18, 2021 corresponding to M >= 6.5 events in a 300 km circular area ranges from 43 to 94%, with the scores of Jakarta (43), Surabaya (89), Bandung (69), Semarang (48), Serang (47), and Yogyakarta (59). This means, for example, that Surabaya has progressed significantly in the regional cycle of large earthquakes, whereas Yogyakarta is about midway in its seismic cycle. We observe that a change in magnitude threshold or geographic area has a consistent impact on the nowcast scores. These findings not only enable a rapid yet meaningful way to rank several cities based on their current exposure to earthquake hazards, but also empower earthquake scientists and policymakers towards better policymaking, land-use planning, earthquake insurance, disaster risk mitigation, and social awareness with respect to the seismically active island of Java.