The tectonic setting of Timor–Leste and Eastern Indonesia comprises of a complex transition from oceanic lithosphere subduction to arc-continental collision. To better understand the deformation and convergent-zone structure of the region, we derive a new catalog of earthquake hypocenters and magnitudes from a temporary deployment of five years of continuous seismic data using an automated processing procedure. This includes a machine-learning phase picker, EQTransformer, and a sequential earthquake association and location workflow. We detect and locate ∼19,000 events during 2014–2018, which demonstrates that it is possible to characterize earthquake sequences from raw seismic data using a well-trained machine-learning picker for a complex convergent plate setting. This study provides the most complete catalog available for the region for the duration of the temporary deployment, which includes a complex pattern of crustal events across the collision zone and into the back-arc, as well as abundant deep slab seismicity.
The geological structure of southwest Australia comprises a rich, complex record of Precambrian cratonization and Phanerozoic continental breakup. Despite the stable continental cratonic geologic history, over the past five decades the southwest of Western Australia has been the most seismically active region in continental Australia, though the reason for this activity is not yet well understood. The Southwest Australia Seismic Network (SWAN) is a temporary broadband network of 27 stations that was designed to both record local earthquakes for seismic hazard applications and provide the opportunity to dramatically improve the rendering of 3D seismic structure in the crust and mantle lithosphere. Such seismic data are essential for better characterization of the location, depth, and attenuation of the regional earthquakes, and hence understanding of earthquake hazard. During the deployment of these 27 broadband instruments, a significant earthquake swarm occurred that included three earthquakes of local magnitude 4.0 and larger, and the network was supplemented by an additional six short-term nodal seismometers at 10 separate sites in early 2022, as a rapid deployment to monitor this swarm activity. The SWAN experiment has been continuously recording since late 2020 and will continue into 2023. These data are archived at the International Federation of Digital Seismograph Networks (FDSN) - recognized Australian Passive Seismic (AusPass) Data center under network code 2P and will be publicly available in 2025.
<p>The Macquarie Ridge Complex, located at the boundary between Indo-Australian and Pacific plates in the southwest Pacific Ocean, hosts the largest sub-marine earthquakes in the 20<sup>th</sup> century, not associated with ongoing subduction. We deployed 27 ocean-bottom seismometers, of which 15 have been recovered successfully, to understand the origin of the sub-marine earthquakes and their potential earthquake and tsunami hazards to Australia and New Zealand. Additionally, we deployed five land-based seismometers on Macquarie Island.</p><p>We explore state-of-the-art processing methods to analyze the new seismic dataset from the retrieved seismic stations. One of the goals is to image the tectonic settings beneath the MRC. Here, we present a first-order tomographic model and its relevant uncertainty estimate of the region constructed from ambient noise surface waves using a probabilistic inversion framework. The tomographic image will be complemented with receiver-based imaging results such as those from P-wave coda autocorrelations and receiver functions to confirm the existence of possible geometries. The results are expected to supply a fresh understanding of the tectonic settings under the MRC and unpuzzle the origin of the significant underwater earthquakes in the 20th century.</p>
<p>The Macquarie Ridge Complex (MRC) constitutes the boundary between the Indo-Australian and Pacific plates in the southwest Pacific Ocean. It accommodates the world&#8217;s most potent sub-marine earthquakes that are not associated with ongoing subduction. To better understand the nature of MRC and its associated earthquakes, we aim to explore the crustal structures using recordings from island-based stations and ocean bottom seismometers (OBS). In particular, these OBSs, which are deployed in the surroundings of Macquarie Island from October 2020 to November 2021, enable us to image the refined oceanic structures beneath the study area. In this study, we obtain the body-wave reflections by computing phase coherence autocorrelations of both ambient noise and earthquake data. Our preliminary reflection profiles by both methods reveal coherent reflected P waves that may be related to Moho and additional structures within the crust and upper mantle.</p>
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