10:45 AM - 12:15 PM
[SSS07-P07] Stress drop of earthquake swarm in/around Suzu City, Ishikawa Prefecture
Keywords:Earthquake swarm, Stress drop, Noto Peninsula
The number of earthquakes in the Noto Peninsula, Ishikawa Prefecture, began to increase in the middle of 2018, and the seismic activity became more active on December 2020, with the largest earthquake of MJMA5.4 on June 19, 2022. In order to elucidate what caused this earthquake swarm, many geophysical studies have been conducted, suggesting that the crustal fluid would play an important role in the activity from several results, such as crustal deformation [Nishimura et al., 2022], hypocentral migration [Hiramatsu, 2022; Amezawa et al., 2022], electrical resistivity structure [Yoshimura et al., 2022], and seismic velocity structure [Nakajima, 2022; Matsubara et al., 2022].
We used the unified hypocenter catalog from the Japan Meteorological Agency (JMA) and waveform data from JMA, Hi-net of the National Research Institute for Earth Science and Disaster Resilience (NIED), the University of Tokyo, and Kyoto University. We analyzed 48 earthquakes (3.0 ≦ MJMA ≦ 5.1) in/around Suzu City from January 2018 to November 2022 as target earthquakes (TEQ). We also used hypocenters relocated by using the double-difference method [Waldhauser and Ellsworth, 2000].
We followed the analysis method of Yamada et al. [2021]. We treated earthquakes close (within 1 km distance) to TEQ as empirical Green's function earthquakes (EGF). In the analysis, we used three time windows after S-wave arrival for the calculation of the spectrum [Imanishi and Ellsworth, 2006] For the two horizontal components of velocity waveforms, we calculated the spectral ratio of TEQ to EGF at each station. We estimated the optimum corner frequencies from the spectral ratios. We used the seismic moment values from the F-net CMT solution if available, otherwise assumed that the moment magnitude is equal to MJMA, and calculated the stress drop from the corner frequency [Madariaga, 1976]. The stress drop of each TEQ was estimated as the logarithmic average of the stress drop at all analyzed stations.
The average value of the stress drops estimated from the S-waves of 48 earthquakes is 14 MPa. The stress drops obtained in this study satisfy a scaling law between the seismic moment and the corner frequency (Mo ∝ fC-3). We recognize variations in the stress drop in space and time. A temporal variation in stress drop might link to the variation in seismic activity. Stress drops in the north cluster are likely to be larger at the edges of the cluster.
In the analysis of this study, we used data from the Japan Meteorological Agency, National Research Institute for Earth Science and Disaster Resilience (NIED) Hi-net and F-net, Earthquake Research Institute, University of Tokyo, and Disaster Prevention Research Institute, Kyoto University. In addition, this work was partly supported by JSPS KAKENHI Grant Number JP22K19949.
We used the unified hypocenter catalog from the Japan Meteorological Agency (JMA) and waveform data from JMA, Hi-net of the National Research Institute for Earth Science and Disaster Resilience (NIED), the University of Tokyo, and Kyoto University. We analyzed 48 earthquakes (3.0 ≦ MJMA ≦ 5.1) in/around Suzu City from January 2018 to November 2022 as target earthquakes (TEQ). We also used hypocenters relocated by using the double-difference method [Waldhauser and Ellsworth, 2000].
We followed the analysis method of Yamada et al. [2021]. We treated earthquakes close (within 1 km distance) to TEQ as empirical Green's function earthquakes (EGF). In the analysis, we used three time windows after S-wave arrival for the calculation of the spectrum [Imanishi and Ellsworth, 2006] For the two horizontal components of velocity waveforms, we calculated the spectral ratio of TEQ to EGF at each station. We estimated the optimum corner frequencies from the spectral ratios. We used the seismic moment values from the F-net CMT solution if available, otherwise assumed that the moment magnitude is equal to MJMA, and calculated the stress drop from the corner frequency [Madariaga, 1976]. The stress drop of each TEQ was estimated as the logarithmic average of the stress drop at all analyzed stations.
The average value of the stress drops estimated from the S-waves of 48 earthquakes is 14 MPa. The stress drops obtained in this study satisfy a scaling law between the seismic moment and the corner frequency (Mo ∝ fC-3). We recognize variations in the stress drop in space and time. A temporal variation in stress drop might link to the variation in seismic activity. Stress drops in the north cluster are likely to be larger at the edges of the cluster.
In the analysis of this study, we used data from the Japan Meteorological Agency, National Research Institute for Earth Science and Disaster Resilience (NIED) Hi-net and F-net, Earthquake Research Institute, University of Tokyo, and Disaster Prevention Research Institute, Kyoto University. In addition, this work was partly supported by JSPS KAKENHI Grant Number JP22K19949.