Earthquake monitoring of the Baribis Fault near Jakarta, Indonesia, using borehole seismometers

Abstract

The geological setting of Jakarta and its immediate surroundings are poorly understood, yet it is one of the few places in Indonesia that is impacted by earthquakes from both the Java subduction zone and active faults on land. In this study, a borehole seismic experiment with low noise characteristics was deployed to record seismic activity on the ~ E-W oriented Baribis Fault, which is ~ 130 km long, passes to the south of Jakarta, and is only ~ 20 km away at its nearest point. A primary objective of this study is to determine whether this fault is seismically active, and therefore, whether it might pose a threat to nearby population centers, including Jakarta in particular. A total of seven broadband instruments that spanned Jakarta and the surrounding region were installed between the end of July 2019 and August 2020, during which time we were able to detect and locate 91 earthquakes. Two earthquakes were located close to the Baribis Fault line, one of which was felt in Bekasi (southeast of Jakarta) where it registered II-III on the Modified Mercalli Intensity (MMI) scale. The focal mechanism solutions of these events indicate the presence of a thrust fault, which is in good agreement with previous studies, and suggest that the Baribis Fault is active.