5:15 PM - 7:15 PM
[SSS12-P08] Spatiotemporal Distribution of Seismic Activity Occurring Simultaneously with the Boso Slow Slip Events
Keywords:SSE, clustering, hypocenter relocation, DBSCAN
Slow slip is a phenomenon where the fault movement occurs slowly without generating seismic waves. Off the Boso Peninsula, these Slow Slip Events (hereafter referred to as SSE) occur periodically. Previous studies have mainly analyzed slip distributions (Ozawa et al., 2008, 2019; Meng et al., 2022) and slip velocities (Fukuda, 2018) using GNSS and InSAR. In addition, there have been studies on the moment release, magnitude and temporal evolution of earthquake occurrence (Meng et al., 2022; Fukuda, 2018), and the relationship between the increase in background seismicity and the timing of SSEs (Reverso et al., 2016). However, few studies focusing on the spatiotemporal distribution of seismic activity that accompanies SSE, and the detailed characteristics of this seismic activity remain unclear. Therefore, the purpose of this study is to investigate the spatial and temporal evolution of earthquakes triggered during SSE.
We used JMA earthquake data from January 2000 to July 2024 and waveform data from February 2005 to July 2024. For focal mechanisms, we used F-net data from January 2000 to July 2024.
First, we relocated earthquake using hypoDD (Waldhauser and Ellsworth, 2000). This method determined the locations of earthquakes by minimizing the difference between observed and theoretical travel time differences for pairs of co-located earthquakes. Then, we carried out the earthquake clustering using DBSCAN (Density-Based Spatial Clustering of Applications with Noise) (Martin et al., 1996), which regards a high-density region of earthquakes as cluster and classify the entire earthquakes into several distinct clusters.
We revealed that the earthquakes occur at shallower depths compared to the upper surface of the Philippine Sea plate model (Hirose et al., 2008). We further identified several clusters of earthquakes that occur near the boundaries of the Philippine Sea plate and Pacific plate. As mentioned above, some of these clusters include earthquakes that occurred at shallower depths than the upper surface of the Philippine Sea plate. To verify whether the earthquakes in these clusters occurred as thrust earthquakes along the upper surface of the Philippine Sea plate, we examined focal mechanisms from F-net. While some earthquakes showed mechanisms different from low-angle thrust faults, we found that most earthquakes occurred at the plate boundary.
In the future study, we plan to perform earthquake relocation separately for each cluster to improve accuracy of hypocenter distributions. We are going to investigate the spatiotemporal distributions of seismic activity during each SSE period.
Acknowledgements: We used JMA unified hypocenter catalog and travel time data. We also used seismograms from JMA, NIED Hi-net, National Universities and CMT solutions from NIED F-net.
We used JMA earthquake data from January 2000 to July 2024 and waveform data from February 2005 to July 2024. For focal mechanisms, we used F-net data from January 2000 to July 2024.
First, we relocated earthquake using hypoDD (Waldhauser and Ellsworth, 2000). This method determined the locations of earthquakes by minimizing the difference between observed and theoretical travel time differences for pairs of co-located earthquakes. Then, we carried out the earthquake clustering using DBSCAN (Density-Based Spatial Clustering of Applications with Noise) (Martin et al., 1996), which regards a high-density region of earthquakes as cluster and classify the entire earthquakes into several distinct clusters.
We revealed that the earthquakes occur at shallower depths compared to the upper surface of the Philippine Sea plate model (Hirose et al., 2008). We further identified several clusters of earthquakes that occur near the boundaries of the Philippine Sea plate and Pacific plate. As mentioned above, some of these clusters include earthquakes that occurred at shallower depths than the upper surface of the Philippine Sea plate. To verify whether the earthquakes in these clusters occurred as thrust earthquakes along the upper surface of the Philippine Sea plate, we examined focal mechanisms from F-net. While some earthquakes showed mechanisms different from low-angle thrust faults, we found that most earthquakes occurred at the plate boundary.
In the future study, we plan to perform earthquake relocation separately for each cluster to improve accuracy of hypocenter distributions. We are going to investigate the spatiotemporal distributions of seismic activity during each SSE period.
Acknowledgements: We used JMA unified hypocenter catalog and travel time data. We also used seismograms from JMA, NIED Hi-net, National Universities and CMT solutions from NIED F-net.