10:45 〜 12:15
[MAG32-P02] Detection, location and characterization of seismic swarms associated with ridge subduction
キーワード：subduction mode, seafloor seismic observation, The 1960 Valdivia earthquake
The Chile subduction zone megathrust fault is a 7000 km long that extends from the Nazca Ridge on the north to the Chile Rise on the south. At the southern margin where an active spreading center of the Chile Ridge currently subducts beneath the South American plate, three plates form a triple junction of the Chile Triple Junction in a perpendicular Ridge-Trench-Trench configuration. This region is periodically affected by devastating earthquakes with Mw larger than 8, including the greatest one of the 1960 Valdivia earthquake with Mw 9.5. The rapture of the 1960 Valdivia earthquake initiated about 1000 km further north from the Chile Triple Junction, propagated southwards and stopped there, where seismic activity is significantly relative low due to the assimilation of the slowly subducting hot new crust.
We recently performed a seismic array observation on the seafloor in the vicinity of the Chile Triple Junction for two years since January 2019 (Ito et al., 2022). The array was composed of seven stations with a 360-s broadband sensor (CMG-3T, Güralp systems ltd.) including two broadband systems equipped with a differential pressure gauge (Araki and Sugioka, 2009) and five stations with a 1-Hz sensor (LE-3Dlite, Lennartz electronics GmbH). On 26th December 2020 during the observation period, three sequence earthquakes with magnitudes larger than 4.3 occurred at around the Chile Triple Junction beneath the array, which was accompanied with numerous earthquakes starting 2 days before for at least one month. We tried to detect to determine their hypocenters using an envelope correlation method for the band passed waveform (Ide et al., 2008). Most of these earthquakes found to occur at the shallow depth just along the Chile Ridge currently subducting.
We recently performed a seismic array observation on the seafloor in the vicinity of the Chile Triple Junction for two years since January 2019 (Ito et al., 2022). The array was composed of seven stations with a 360-s broadband sensor (CMG-3T, Güralp systems ltd.) including two broadband systems equipped with a differential pressure gauge (Araki and Sugioka, 2009) and five stations with a 1-Hz sensor (LE-3Dlite, Lennartz electronics GmbH). On 26th December 2020 during the observation period, three sequence earthquakes with magnitudes larger than 4.3 occurred at around the Chile Triple Junction beneath the array, which was accompanied with numerous earthquakes starting 2 days before for at least one month. We tried to detect to determine their hypocenters using an envelope correlation method for the band passed waveform (Ide et al., 2008). Most of these earthquakes found to occur at the shallow depth just along the Chile Ridge currently subducting.