The 26 September 2019 Mw 6.5 Ambon earthquake has been the largest instrumentally recorded event to occur in Ambon, the capital city of Maluku Islands, eastern Indonesia, and ruptured a previously unmapped active fault. In this study, we use seismic and geodetic data to investigate the source characteristics of the event. Our results show that the rupture process was complex in both the rupture initiation and slip directions. In addition, the rupture was mostly strike-slip motion with normal component and pure reverse slip in the north of the inverted fault. Our analysis of campaign and continuous Global Positioning System (GPS) velocity fields estimates that the fault has a 4.9 [4.0, 5.5] mm/yr slip rate with an earthquake recurrence interval of 115 [102, 141] yr. In addition, a comparison of the horizontal strain-rate tensor derived from GPS velocity fields with historical earthquake data shows that Ambon Island and the nearby regions have a high strain accumulation rate correlated with the distribution of Mw≥6 earthquakes, indicating that the regions are seismically active and possibly will experience more Ambon-type earthquakes in the future.
On September 12, 2007, a M8.5 megathrust earthquake occurred along the Sunda trench near Bengkulu, West Sumatra. GPS data in Sumatra have indicated the coseismic and postseismic deformations resulting from this earthquake. Our estimate of coseismic displacements suggests that the earthquake displaced up to ~1.8m at GPS stations located north of the epicenter. Moreover, our principal strain estimation in the region suggests that the maximum coseismic extensional strain is ~40 ppm. Our analysis of GPS data in the region suggests that the postseismic decay of the 2007 Bengkulu earthquake was 46 days, estimated using a logarithmic function.
Banda arc is a product of complex interactions between the Eurasian, Australian, Pacific and Philippine Sea plates. As a result of this tectonic interaction, the Banda arc has undergone significant deformation of the crust, both in the horizontal and vertical directions. In this study, we performed a time-series data analysis of displacement in vertical components. A total of 16 permanents GPS observations from 2008 to 2013 were collected and analysed in this study. The GPS sites spread around the Banda arc area from Bali island in the south to Ambon in the north. This is the first research on vertical deformation analysis carried out in this area. The results of this study show that 3 GPS sites experience a subsidence, which are BANI, CAMB and CTOA, while the 13 others experience an uplift mechanism. The spatial pattern of vertical deformation obtained from this research will provide insight about tectonic conditions and can then be used as a basis for conducting seismic hazard analysis in the Banda arc.
Eastern Indonesia lies in a complex tectonic region due to the interaction of four major tectonic plates: the Australian Plate, Pacific Plate, Philippine Sea Plate, and Sunda Block. Therefore, this region hosted some destructive seismic activities as well as tectonic deformation, such as the Mw 7.5 Palu Earthquake, the sequences of the 2018 Lombok Earthquake, and the Mw 6.5 Ambon Earthquake in 2019. Our work proposes a recent study on crustal deformation in Eastern Indonesia inferred from Global Positioning System (GPS) velocity field. We used GPS data from the observations of 49 permanent and 61 campaign stations from 2010 to 2018. Here, our velocity field result represents long-term tectonic deformation regions in Eastern Indonesia continuously, from Bali in the west to Papua in the east, demonstrated both in the ITRF 2008 and the Sunda reference frames. The spatial pattern of velocity field map collected from this research will give an initial insight into the present-day tectonic condition in Eastern Indonesia and then can be used to improve our ability to assess this area’s earthquake potential.
Summary
On the 15th of January 2021 (local date), an MW 6.2 earthquake struck the Mamuju and Majene regions of West Sulawesi, Indonesia. This event killed more than one hundred inhabitants, leaving at least thirty thousand people displaced from their homes, and damaged almost eight thousand buildings within a radius of ∼30 km from the mainshock's epicentre location (as shown on our damage proxy map). This event was generated by an active fault that continues to the Makassar Strait Thrust (MST) offshore West Sulawesi. The hazard potential of this fault remains poorly understood. In this study, we use seismic and Global Positioning System (GPS) data to investigate the source characteristics of the mainshock. The results suggest that the mainshock partially ruptured one segment of the MST, activated a secondary fault structure, and likely brought the up-dip unruptured section of the MST segment closure to failure. Our analysis of interseismic GPS velocities indicates that the Mamuju and Majene regions have a higher crustal strain rate than other nearby regions. The results (partial rupture of the MST segment, the up-dip unruptured section of the MST, and high strain rate in the Mamuju and Majene regions) together suggest a significant seismic hazard potential in West Sulawesi, particularly in the Mamuju and Majene areas.
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