Long-term array observation by ocean bottom seismometers at the Chile Triple Junction

Abstract

Seafloor seismic observations were conducted twice in the vicinity of the Chile Triple Junction (CTJ) in order to investigate the crustal activities associated with the subduction of the hot ridge. Herein, we present the details of the most recent seismic observation for the two-year period between January 2019 and January 2021. Furthermore, the hypocenter location, magnitude, and focal mechanisms of the local earthquakes were revealed by analyzing the data from both deployments, including the one conducted between 2009 and 2010. In total, more than 2100 local earthquakes were detected during the two observation periods. In both observations, earthquakes were found to have actively occurred along the Chile Ridge and the Darwin Fracture Zone. The magnitudes of these earthquakes range from −0.3 to 5.0. From the events cataloged during the time period 2019 to 2021, a clear seismicity gap is observed at 46.4°S with the predominant faulting type differing across this divide. North of the seismicity gap, normal faulting earthquakes periodically occur along the Chile Ridge, thereby indicating continuous ridge opening. By contrast, the earthquakes to the south of the seismicity gap, where the Chile Ridge has already been subducted, occurred intermittently and are dominated by reverse faulting. The latter earthquakes are associated with the Antarctic plate subduction. We propose that a local transform fault, with E-W strike direction, exists 10 km north of the seismicity gap, based on the hypocenter locations and focal mechanisms of three M > 4 earthquakes. This local transform fault was probably formed by the effect of the active ridge subduction.© 2017 Elsevier Inc. All rights reserved.