5:15 PM - 6:45 PM
[U15-P16] Spatio-Temporal Distribution of Repeating Earthquakes in the Noto Peninsula Earthquake Swarm
Repeating earthquakes (repeaters) are earthquakes in which similar waveforms are observed as a result of the same rupture process at the identical location on a fault. The mechanism of occurrence has been studied at plate-boundary repeaters, and the repeaters are interpreted as repeating ruptures of an isolated asperity caused by surrounding aseismic slip. However, repeating earthquakes have also been found in crustal earthquakes and fluid injection-induced earthquakes, and further verification is needed to understand the mechanism of repeating earthquakes that occur other than at plate boundaries.
In this study, we detected repeating earthquakes in the Noto Peninsula earthquake swarm, which became active around the end of 2020. This earthquake swarm activity has been suggested to be related to fluids migrations, which may activate aseismic slip and trigger repeating earthquakes. We detected repeating earthquakes and investigated their spatio-temporal distribution for better understanding of the mechanism of repeating earthquakes in the crust, and also discussed the relationship between aseismic slip inferred from the repeating earthquakes and swarm activity.
First, we performed hypocenter relocation using the double-difference method based on waveform cross-correlations. Then, repeating earthquakes were identified based on the waveform similarity and source area overlap for M2-4 earthquakes that occurred in the northeastern Noto Peninsula from January 2020 to January 1, 2024. As a result, 236 earthquakes, which is 12.8% of the total number of earthquakes analyzed, were identified as repeating earthquakes, and divided into 102 series. Based on the characteristics of the spatio-temporal distribution, the mechanism of the repeating earthquakes in this earthquake swarm can be explained in the same way as that proposed for plate-boundary repeaters. There were also repeating earthquake pairs with magnitude differences exceeding 1.0, suggesting temporal variations in the stress drop.
The repeating earthquakes began to occur after May 2021, when swarm activity increased in the western and northern cluster, and a short period of intensive outbreaks (burst-type repeater) was observed mainly in the northern cluster during the period from an M5.1 earthquake in September 2021 to an M5.4 earthquake in June 2022. During this period, aseismic slip was likely to have occurred in shallower areas (10-14 km depth) in conjunction with aseismic slip geodetically detected at ~15km depth.
In this study, we detected repeating earthquakes in the Noto Peninsula earthquake swarm, which became active around the end of 2020. This earthquake swarm activity has been suggested to be related to fluids migrations, which may activate aseismic slip and trigger repeating earthquakes. We detected repeating earthquakes and investigated their spatio-temporal distribution for better understanding of the mechanism of repeating earthquakes in the crust, and also discussed the relationship between aseismic slip inferred from the repeating earthquakes and swarm activity.
First, we performed hypocenter relocation using the double-difference method based on waveform cross-correlations. Then, repeating earthquakes were identified based on the waveform similarity and source area overlap for M2-4 earthquakes that occurred in the northeastern Noto Peninsula from January 2020 to January 1, 2024. As a result, 236 earthquakes, which is 12.8% of the total number of earthquakes analyzed, were identified as repeating earthquakes, and divided into 102 series. Based on the characteristics of the spatio-temporal distribution, the mechanism of the repeating earthquakes in this earthquake swarm can be explained in the same way as that proposed for plate-boundary repeaters. There were also repeating earthquake pairs with magnitude differences exceeding 1.0, suggesting temporal variations in the stress drop.
The repeating earthquakes began to occur after May 2021, when swarm activity increased in the western and northern cluster, and a short period of intensive outbreaks (burst-type repeater) was observed mainly in the northern cluster during the period from an M5.1 earthquake in September 2021 to an M5.4 earthquake in June 2022. During this period, aseismic slip was likely to have occurred in shallower areas (10-14 km depth) in conjunction with aseismic slip geodetically detected at ~15km depth.