Indonesia is known for extremely active plate tectonics and a series of gigantic earthquakes including the well-known 2004 Mw 9.3 earthquake. Since 2000, about 50% of global seismic energy release took place in and around the Sumatra island, despite that its area only occupies a few percent of the earth surface. Yet, limited seismological studies have been conducted in Indonesia, primarily due to the lack of high-quality seismic observations and innovative analysis of available datasets. Starting from 2018, we have overcome tremendous logistic difficulties and deployed seismometers in areas of interest to acquire valuable nearfield seismic data. For instance, we deployed seismometers rapidly after the 2018 Lombok and Palu earthquake sequences. The analysis of these datasets has led to at least four manuscripts, including the finding of squeezing of the seismogenic zones caused by the Rinjani volcano that controls the rupture complexity of the 2018 Lombok earthquake sequence (Lythgoe et al, 2021); rapid post-seismic slip that filled in the spatial gaps between the asperities of the first Mw6.9 earthquake in the 2018 Lombok sequence (Wei et al., 2021); segmented supershear rupture of the 2018 Mw7.5 Palu earthquake boosted by the deep slip on a less mature fault (Wei et al., 2021); and identify aftershock signature of the supershear rupture of the 2018 Mw7.5 Palu earthquake (Muzli et al., 2021).
The team's former research fellow Muzli deployed 9 broadband seismometers after the 2016 Mw 6.5 Pidie Jaya earthquake that took place in Aceh, North Sumatra. Our analysis of the data showed that the earthquake was a reactivation of an unidentified secondary fault located ~50 km to the north of the Sumatran fault (Muzli et al., 2018). We also found that the secondary crustal faults in Aceh are much more active than the rest of Sumatra island (Muzli et al., 2018), primarily due to the distributed deformation likely related to the big bend of the subduction plate boundary. More interestingly, a ~30km-long segment of the Sumatran fault in the Aceh region has been creeping (Tong et al., 2018; Muksin et al., 2019). Motivated by these fascinating observations, we have managed to deploy 200 short-period seismometers in Aceh to capture the highly distributed seismicity in the crust and earthquakes/tremors along the creeping segment of the Sumatran fault. The network has been working for 10 months to the date of December 2020, providing the first dense seismic array observations in Sumatra. A series of exciting findings and high-quality papers are expected from this valuable dataset in the near future.
Besides deploying dense seismic arrays, we also developed new methods to explore the historical datasets to study earthquakes in Indonesia. Through modeling and inversion of teleseismic broadband waveform records of past earthquakes, we imaged the ruptured fault planes of the 2005 (Mw6.9) and 2009 (Mw6.7) earthquakes sequences that occurred in the Mentawai seismic gap, the nearest Sumatran subduction segment to Singapore. Our high-resolution earthquake location unambiguously showed that these sequences actually took place on the back-stop faults (Wang et al., 2018), instead of the back-thrust faults as previously considered (Wiseman et al., 2011). Since the method only relies on teleseismic waveform data, it can be generalized to the global earthquake source parameter and fault geometry studies.
- Earth Observatory of Singapore
Wang Xin, Institute of Geology and Geophysics, Chinese Academy of Sciences
Chen Meng, University of Electronic Science and Technology of China
Wenbo Wu, Department of Geoscience, Princeton University
Wang Teng, Peking University
Sri Widiyantoro, Institut Teknologi Bandung
Muksin, Tsunami and Disaster Mitigation Research Center
- Thermal squeezing of the seismogenic zone controlled rupture of the volcano-rooted Flores Thrust. Science Advances. 7(5), (2021).
- Structural Controls on Rupture Extent of Recent Sumatran Fault Zone Earthquakes, Indonesia. Journal of Geophysical Research - Solid Earth. 125(2), (2020).
- Cascading Partial Rupture of the Flores Thrust during the 2018 Lombok Earthquake Sequence, Indonesia. Seismological Research Letters. (2020).
- Hypocenter and Magnitude Analysis of Aftershocks of the 2018 Lombok, Indonesia, Earthquakes Using Local Seismographic Networks. Seismological Research Letters. 91(4), 2152–2162. (2020).
- The 1922 Peninsula Malaysia Earthquakes: Rare Intraplate Seismicity within the Sundaland Block in Southeast Asia. Seismological Research Letters. 91(5), 2531-2545. (2020).