Source mechanism and triggered large aftershocks of the Mw 6.5 Ambon, Indonesia earthquake
Sahara D.P.a, Nugraha A.D.a, Muhari A.b, Rusdin A.A.c, Rosalia S.a, Priyono A.a, Zulfakriza Z.a, Widiyantoro S.a,d, Puspito N.T.a, Rietbrock A.e, Lesmana A.a, Kusumawati D.a, Ardianto A.a, Baskara A.W.a, Halauwet Y.c, Shiddiqi H.A.f, Rafie M.T.a, Pradisti R.a, Mozef P.W.a, Tuakia M.Z.g, Elly E.g
a Global Geophysics Research Group, Institut Teknologi Bandung, Bandung, Indonesia
b National Disaster Management Authority of Indonesia, Jakarta, Indonesia
c Agency for Meteorology, Climatology and Geophysics of Indonesia, Ambon, Indonesia
d Faculty of Engineering, Maranatha Christian University, Bandung, Indonesia
e Geophysical Institute, Karlsruhe Institute of Technology, Karlsruhe, Germany
f Department of Earth Science, University of Bergen, Bergen, N-5007, Norway
g Geological Engineering Study Program, Pattimura University, Ambon, Indonesia
Abstract
© 2020 Elsevier B.V.On September 26, 2019, a significant, Mw 6.5, earthquake shook Ambon region, Indonesia, causing severe damage on the Island(s) of Ambon. Due to the complexity of the fault network and in-situ stress field it was, up to now, not possible to define the fault plane using data from the BMKG regional seismic network. In this study, we analyze the fault plane of the 2019 Ambon earthquake and the reactivation potential of the surrounding faults using local networks. Eleven stations were deployed to monitor the aftershocks from October 18th to December 15th, 2019 augmented with data of four regional stations. During the monitoring period, 1,778 events were identified comprised of 10,938 P- and 10,315 and S- wave arrival times. The locations of aftershock were determined in a stepwise approach, i.e. (i) initial location determination using a non-linear approach, (ii) updating the velocity model, and (iii) relative double-difference relocation. Slip inversion using teleseismic data was performed to infer of high strain relief of the mainshock and to compute its associated static stress transfer (ΔCFF). Based on aftershock distribution and finite fault modeling, we conclude that the Mw 6.5 Ambon earthquake occurred on a N-S oriented fault plane. Two clusters consisting of ~60% of total events are located at both tips of the plane. Another cluster ~30% was sharply aligned in a NE-SW trend, 10 km westward, starting by an Mw 5.2 event on November 2nd, 2019. The b-value of the NE-SW events is ~0.25 lower than the other clusters with a b-value of 0.85±0.14. ΔCFF imparted by the mainshock caused ~0.5 Bar stress increase on the NE-SW fault. We concluded that the NE-SW trend was the reactivation of a preexisting fault crossing Ambon Island. The triggered large aftershock caused further significant damages to already weakened infrastructure and, thus, had the largest mapped damage area.
Author keywords
Aftershock distributions,Double differences,Finite fault modeling,In-situ stress field,Location determination,Monitoring periods,Nonlinear approach,Stepwise approach
Indexed keywords
2019 Ambon earthquake,Fault network,Local seismic network,Source mechanism,Stress transfer
Funding details
[{‘$’: ‘We are grateful to the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) for access to their 2019 Ambon aftershocks data which were used in this study. All figures were made using QGIS. The seismographic station deployment was funded by BNPB. This study was supported in part by research funding from the ITB 2020, awarded to DPS.’}, {‘$’: ‘We are grateful to the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) for access to their 2019 Ambon aftershocks data which were used in this study. All figures were made using QGIS. The seismographic station deployment was funded by BNPB. This study was supported in part by research funding from the ITB 2020, awarded to DPS.’}]