10:15 〜 10:30
[SSS06-06] 東南海・南海地震震源域における地震活動分布とプレート間固着およびスロー地震との関係
キーワード：南海トラフ、海底地震観測、DONET、地震活動
The Nankai Trough subduction zone is well known for repeated M8 class mega-earthquakes, which have occurred at intervals of 100–150 years (Ando, 1975). The area off the Kii Peninsula is key to understanding the seismic behavior of these large earthquakes because it includes the boundary between two of the largest seismogenic segments in the subduction zone, the Tonankai and Nankai segments. The most recent mega-earthquakes in this region, the 1944 Tonankai (Mw8.1) and 1946 Nankaido (Mw8.3) earthquakes, occurred about 75 years ago. For this reason, various seismological and geodetic studies have been carried out in the Nankai Trough. These are revealing the existence of subsurface structural heterogeneities that can control rupture propagation (e.g., Kodaira et al., 2002, 2006), slow seismic phenomena and their distribution (e.g., Nakano et al., 2018; Takemura et al., 2019), and current slip-deficit distribution (e.g., Yokota et al., 2016; Nishimura et al., 2018). However, not much research has been done on regular earthquake activity because of their low activity level and the difficulty in determining the hypocenter location with high accuracy due to offshore condition. Monitoring the spatio-temporal distribution of not only slow earthquakes but also regular earthquakes at the plate boundary is important for studying the occurrence process of large earthquakes.
In this study, we attempted to determine the hypocenter location detected by DONET (Kawaguchi et al., 2011; Kaneda et al., 2015) since 2012 with high accuracy to clarify the seismically active region on the plate boundary of the Nankai Trough. To improve the accuracy of the estimated hypocenter location, we performed seismic tomography by adding DONET data to the previous 3D tomographic study (Yamamoto et al., 2017), and updated the velocity structure and hypocenter location simultaneously.
The spatial characteristics of the updated velocity model are not so different from the previous model (Yamamoto et al., 2017), but the recovery of the checkerboard resolution test is greatly improved. From the obtained hypocenter catalog, we extract earthquakes near the plate boundary based on the plate boundary model (Nakanishi et al., 2018) and found that these earthquakes were localized in several clusters. Most of them are located outside the large slip deficit area suggested by the geodetic data (Nishimura et al., 2018). They also seem not to overlap with the active area of VLFE (Takemura et al., 2019). These spatial relationships indicate the monitoring of regular earthquakes may provide useful information about the interplate coupling status.
In this study, we attempted to determine the hypocenter location detected by DONET (Kawaguchi et al., 2011; Kaneda et al., 2015) since 2012 with high accuracy to clarify the seismically active region on the plate boundary of the Nankai Trough. To improve the accuracy of the estimated hypocenter location, we performed seismic tomography by adding DONET data to the previous 3D tomographic study (Yamamoto et al., 2017), and updated the velocity structure and hypocenter location simultaneously.
The spatial characteristics of the updated velocity model are not so different from the previous model (Yamamoto et al., 2017), but the recovery of the checkerboard resolution test is greatly improved. From the obtained hypocenter catalog, we extract earthquakes near the plate boundary based on the plate boundary model (Nakanishi et al., 2018) and found that these earthquakes were localized in several clusters. Most of them are located outside the large slip deficit area suggested by the geodetic data (Nishimura et al., 2018). They also seem not to overlap with the active area of VLFE (Takemura et al., 2019). These spatial relationships indicate the monitoring of regular earthquakes may provide useful information about the interplate coupling status.