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.

Geodetic Strain of the Baribis Fault Zone in West Java, Indonesia

“…Based on the estimated principal strain rate in Figure 2, our result indicates that, in general, the northeastern Baribis faults zone (108.0 E, 6.5 S) experiences a significant strain rate (> 50 nanostrain/yr) with a significant and dominant compressional strain. This result is in line with the previous study from [9,10] that the northeastern Baribis Fault in southern Jakarta indicates a high compression rate. Furthermore, Figure 3 depicts our result's distribution of the dilatation rate.…”

“…In the case of Baribis Fault, recently called as West Java Back-arc Thrust (WJBT) [5], an earthquake between Mw7.0-8.0 likely occurred on the Baribis Fault on January 22, 1780, followed by the second event between Mw7.0-7.7 on October 10, 1834 [6]. The existence of this fault has also been studied by several researchers, such from geological mapping using seismic reflection [7], Digital Elevation Model [8], borehole data [9,10] from regional continuous Global Positioning System (cGPS) network, geodetic strain rate [3,[11][12][13], and more complete study used morphotectonic data, seismic reflection, electric resistivity profiles, kinematic, structural field measurements, paleoseismological trenching, and sediment dating [5]. However, none of the above studies used more dense GPS networks in the northeastern Baribis Fault close to the Subang and Cirebon area (Figure 1).…”

“…This study extends our previous work on investigating along northeastern Baribis Fault in West Java, which involved more dense GPS stations. Previously, there was much discussion about whether the Baribis Fault was active [9,10,13].…”

“…Figure 1. Distribution of GPS station (cGPS (black squares) and sGPS (blue circles) and seismicities (colored circles) in West Java [4,10]. The black arrows are the GPS velocities in the ITRF2014 [14].…”

Fuzzy Interpolation Curve Modelling of Earthquake Magnitude Data

“…Then, at the same time, the earthquake magnitude data are implemented to the fuzzy interpolation curve modeling which has uncertainty issues on the data collection. Many research has been done about earthquakes such as [20][21][22][23]. Also, research that focuses on solving uncertainty problems had been discussed [24][25][26][27] and research that involves spline function as spline interpolation can be referred to by [28].…”