Earthquake Swarm Recorded by an Ocean Bottom Seismic Array in Southwest Offshore of Taiwan in October, 2005

Abstract

We conduct a detailed analysis of the seismic records for 406 marine earthquakes in SW offshore of Taiwan recorded by a small OBS array during 7 -12 October 2005. The spatial distribution of the events, which included a complete main shock-aftershock sequence, show concentration in a vertical chain reaching 40 km in depth and that the deeper events slightly turns to the NE toward the Taiwan island. We use these recorded data to construct a 1-D layered velocity model for the local lithosphere. The model puts the Moho at around 13 km in depth and plate seismogenic thickness at about 40 km for the studied area. Our observations reveal that the local seismogenic structure is consistent with the character of the oceanic-origin crust and a non-subducting related mechanism. We also examine the polarizations of P-, S-wave first arrivals and P-to-SV ratios in the waveform to obtain focal mechanism solutions for a total of 26 events. However, their solutions particularly show a non-unique deforming comportment for the strain releases, implying a strain rebound corresponding to the back-and-forth motion and also affected by the complexity of the pre-existing structure in the region.

Seismic evidence for a slab tear at the Puerto Rico Trench

“…Where station distribution is poor, sampling of the focal sphere is incomplete; therefore, the addition of S / P amplitude ratios can supplement the first‐arrival information [ Hardebeck and Shearer , , ; Julian and Foulger , ; Kisslinger , ; Snoke et al ., ]. Including these ratios in focal mechanism calculations has also proved successful in regions with limited data coverage and/or events of small magnitude, such as the Alpine Fault in New Zealand, offshore SW Taiwan, Atotsugawa Fault in central Japan, Southern California, São Miguel Island, and western Skagerrak [ Boese et al ., ; Chang et al ., ; Imanishi et al ., ; Kilb and Hardebeck , ; Silva et al ., ; Sørensen et al ., ; Yang et al ., ].…”

“…Clear understanding of the geometry and mechanisms within the subducting slab depends on the accuracy of the earthquake hypocenters. Temporary deployments of OBS have been shown to resolve the location bias of land‐based seismographic networks in submarine‐dominated tectonic settings, such as the southern Tyrrhenian Sea, Taiwan, southern New Hebrides arc, central Aleutian subduction zone, South Shetland Islands, offshore Japan, northern Ecuador, and the East Pacific Rise [ Barberi et al ., ; Begnaud et al ., ; Chang et al ., ; Coudert et al ., ; Dahm , ; Frohlich et al ., ; Maurice et al ., ; Montagner et al ., ; Nishizawa et al ., ; Pontoise and Monfret , ; Pulliam et al ., ; Shen et al ., ; Webb , ].…”

One Year of Seismicity Recorded Through Ocean Bottom Seismometers Illuminates Active Tectonic Structures in the Ionian Sea (Central Mediterranean)

“…Since the '80s, thanks to the technological development, OBSs and seafloor observatories have been deployed in different regions of the world, mainly to improve location of earthquakes occurring offshore and in coastal areas, complementing data from land based networks (e.g., Lawton et al, 1982;Hino et al, 1996;Hsiao et al, 2014), and to perform 1D and 3D seismic velocity crustal studies in the offshore (e.g., Husen et al, 2000;Montuori et al, 2007;Chang et al, 2008;Monna et al, 2013;Sgroi et al, 2021).…”

Outer trench slope extension to frontal wedge compression in a subducting plate

“…The MicrOBS data logger is stable and e ciently recorded ground motion in the frequency band of 1-100 Hz with a peak response at 4.5 Hz (Auffret et al 2004). Seismic airgun shots proceeded OBS deployments to relocate the sea oor OBS stations and to retrieve the recording directions of the two horizontal components (Chang et al 2008).…”