11:00 AM - 1:00 PM
[SSS10-P06] Regional dependence in source characteristics of interplate earthquakes off northeastern Japan and off Chile
Keywords:interplate earthquake, Japan trench, Peru-Chile trench, source scaling relationship, regional dependence
In setting the parameters of characterized source models for predicting ground motions during interplate earthquakes, it is appropriate to use a source scaling relationship that takes into account differences between oceanic plates (Headquarters for Earthquake Research Promotion, 2020). In this study, we collected and compiled the results of previous studies mainly on source inversion and strong motion generation area (SMGA) models for interplate earthquakes off northeastern Japan (mainly along the Japan trench) and off Chile (along the Peru-Chile trench), which is a seismically active region. Using these data, we investigated the regional dependence of source characteristics.
The data were collected from 23 earthquakes in northeastern Japan (MW 6.2-9.1) and 12 earthquakes in Chile (MW 6.9-8.8). The data for southwestern Japan such as the Nankai and Sagami troughs were not included because of their limited number. We obtained outer fault parameters (rupture area and average slip) and inner fault parameters (combined area of large slip areas (LSAs), combined area of SMGAs, and short-period spectral level) by using the criteria of Somerville et al. (1999) and Murotani et al. (2008) and the equation of Dan et al. (2001).
A 2-stage source scaling relationship (Tajima et al., 2013; Allen and Hayes, 2017) has been proposed for interplate earthquakes. Most of our data were the 1st-stage earthquakes (MW <= 8.4). The rupture areas of northeastern-Japan earthquakes can be well reproduced by the 1st-stage scaling relationship of Murotani et al. (2008). This fact is consistent with the validation of Miyakoshi et al. (2021). We found that the rupture area of the Chilean earthquake is larger than that of the northeastern-Japan earthquake. For the same MW, the rupture area of the Chilean earthquake is about twice as large as the northeastern-Japan earthquake. On the other hand, the average slip of the Chilean earthquake is smaller than that of the northeastern-Japan earthquake. These findings are supported by the result of Allmann and Shearer (2009), which showed that the average stress drop of the Chilean earthquake is smaller than that of the northeastern-Japan earthquake.
The combined area of LSAs based on source inversions has the same regional difference as the rupture area. This leads to the fact that there is no regional difference in the ratio of LSAs to rupture area (northeastern Japan: 21%, Chile: 23%). The combined areas of SMGAs for northeastern-Japan earthquakes, which were obtained by the analyses using empirical Green's functions, are relatively close to the scaling relationship for the combined area of SMGAs proposed by Satoh (2010). Chilean earthquakes have slightly larger combined areas of SMGAs than Satoh (2010). Note that, within each region, the combined area of SMGAs has large variability between events. Thus, it is difficult to conclude any regional difference in the combined area of SMGAs. As a source characteristic common to both regions, we can conclude that SMGA have a dimension not exceeding about half of LSA (e.g., Satoh, 2010; Tajima et al., 2013, Guo et al., this meeting). The short-period spectral levels for both regions are roughly comparable, although Chile has slightly larger variability between events than northeastern Japan.
The regional dependence of source characteristics in this study can serve as important information for the study on the variability of source parameters. As a future task, an investigation of the differences in ground motions observed during similar MW earthquakes between Chile and northeastern Japan is important for supporting our conclusions.
Acknowledgements: This study was based on the 2021 research project “the study on the characterized source model for interplate earthquakes” by the Nuclear Regulation Authority, Japan.
The data were collected from 23 earthquakes in northeastern Japan (MW 6.2-9.1) and 12 earthquakes in Chile (MW 6.9-8.8). The data for southwestern Japan such as the Nankai and Sagami troughs were not included because of their limited number. We obtained outer fault parameters (rupture area and average slip) and inner fault parameters (combined area of large slip areas (LSAs), combined area of SMGAs, and short-period spectral level) by using the criteria of Somerville et al. (1999) and Murotani et al. (2008) and the equation of Dan et al. (2001).
A 2-stage source scaling relationship (Tajima et al., 2013; Allen and Hayes, 2017) has been proposed for interplate earthquakes. Most of our data were the 1st-stage earthquakes (MW <= 8.4). The rupture areas of northeastern-Japan earthquakes can be well reproduced by the 1st-stage scaling relationship of Murotani et al. (2008). This fact is consistent with the validation of Miyakoshi et al. (2021). We found that the rupture area of the Chilean earthquake is larger than that of the northeastern-Japan earthquake. For the same MW, the rupture area of the Chilean earthquake is about twice as large as the northeastern-Japan earthquake. On the other hand, the average slip of the Chilean earthquake is smaller than that of the northeastern-Japan earthquake. These findings are supported by the result of Allmann and Shearer (2009), which showed that the average stress drop of the Chilean earthquake is smaller than that of the northeastern-Japan earthquake.
The combined area of LSAs based on source inversions has the same regional difference as the rupture area. This leads to the fact that there is no regional difference in the ratio of LSAs to rupture area (northeastern Japan: 21%, Chile: 23%). The combined areas of SMGAs for northeastern-Japan earthquakes, which were obtained by the analyses using empirical Green's functions, are relatively close to the scaling relationship for the combined area of SMGAs proposed by Satoh (2010). Chilean earthquakes have slightly larger combined areas of SMGAs than Satoh (2010). Note that, within each region, the combined area of SMGAs has large variability between events. Thus, it is difficult to conclude any regional difference in the combined area of SMGAs. As a source characteristic common to both regions, we can conclude that SMGA have a dimension not exceeding about half of LSA (e.g., Satoh, 2010; Tajima et al., 2013, Guo et al., this meeting). The short-period spectral levels for both regions are roughly comparable, although Chile has slightly larger variability between events than northeastern Japan.
The regional dependence of source characteristics in this study can serve as important information for the study on the variability of source parameters. As a future task, an investigation of the differences in ground motions observed during similar MW earthquakes between Chile and northeastern Japan is important for supporting our conclusions.
Acknowledgements: This study was based on the 2021 research project “the study on the characterized source model for interplate earthquakes” by the Nuclear Regulation Authority, Japan.