10:45 AM - 12:15 PM
[SSS10-P15] The relationship between background seismicity rate and strain rate in and around the strain concentration zones in Japan
Keywords:Seismicity, Strain rate, HIST-ETAS model
Earthquakes are caused by the stress accumulation in the earth’s interior due to the relative plate motion. Therefore, it is considered that the strain rate estimated from geodetic data may correlate with seismicity, and this relationship has been discussed in several areas in the world (e.g., Zeng et al., 2018). In this study, we investigate the spatial correlation between the strain rate estimated using GNSS data and the background seismicity rate for the crustal seismicity in Japan.
We used the JMA unified catalog for the hypocenter catalog. We applied the Hierarchical Space-Time Epidemic Type Aftershock Sequence (HIST-ETAS) model (e.g., Ogata, 2004) to the M > 3.0 crustal earthquakes that occurred from 1980 through 2010 and were located at < 25km. In order to remove aftershocks, we calculated the probability that each event is a background event using the estimated HIST-ETAS parameters, and used these values for the calculation of background seismicity in each region. We evaluated background seismicity in each 0.2°×0.2° grid and compared it with the maximum shear strain rate, the second invariant of the strain rate, and the maximum absolute principal strain rate in the horizontal plane estimated using the GNSS data (1997-1999 and 2006-2009) by Fukahata et al. (2022). The study regions are in and around the four strain concentration zones: the Niigata Kobe Tectonic Zone, the Ou Backbone Range, the San-in shear zone, and the Beppu-Shimabara graben.
We found spatial variations in background seismicity in and around the Niigata Kobe Tectonic zone and the Ou Backbone Range positively correlate with that in the strain rate. As for Ou Backbone Range, the second invariant of the strain rate and the maximum absolute principal strain rate in the horizontal plane are better correlated with background seismicity compared with the maximum shear strain rate. They are positively correlated when evaluating background seismicity during the same time period as the GNSS data used to estimate strain rate (1997-1999 and 2006-2009), but its correlation is insignificant due to the reduced number of data.
No significant correlation was found in and around the San-in shear zone and the Beppu-Shimabara graben. It is possible that the results could be improved by appropriately removing deformations attributed to interplate coupling and non-tectonic local deformations.
Acknowledgements: The JMA catalog was used; the code of Ogata et al. (2021) was used to estimate parameters of the HIST-ETAS model. I thank T. Okazaki for providing strain rate data (Fukahata et al., 2022).
We used the JMA unified catalog for the hypocenter catalog. We applied the Hierarchical Space-Time Epidemic Type Aftershock Sequence (HIST-ETAS) model (e.g., Ogata, 2004) to the M > 3.0 crustal earthquakes that occurred from 1980 through 2010 and were located at < 25km. In order to remove aftershocks, we calculated the probability that each event is a background event using the estimated HIST-ETAS parameters, and used these values for the calculation of background seismicity in each region. We evaluated background seismicity in each 0.2°×0.2° grid and compared it with the maximum shear strain rate, the second invariant of the strain rate, and the maximum absolute principal strain rate in the horizontal plane estimated using the GNSS data (1997-1999 and 2006-2009) by Fukahata et al. (2022). The study regions are in and around the four strain concentration zones: the Niigata Kobe Tectonic Zone, the Ou Backbone Range, the San-in shear zone, and the Beppu-Shimabara graben.
We found spatial variations in background seismicity in and around the Niigata Kobe Tectonic zone and the Ou Backbone Range positively correlate with that in the strain rate. As for Ou Backbone Range, the second invariant of the strain rate and the maximum absolute principal strain rate in the horizontal plane are better correlated with background seismicity compared with the maximum shear strain rate. They are positively correlated when evaluating background seismicity during the same time period as the GNSS data used to estimate strain rate (1997-1999 and 2006-2009), but its correlation is insignificant due to the reduced number of data.
No significant correlation was found in and around the San-in shear zone and the Beppu-Shimabara graben. It is possible that the results could be improved by appropriately removing deformations attributed to interplate coupling and non-tectonic local deformations.
Acknowledgements: The JMA catalog was used; the code of Ogata et al. (2021) was used to estimate parameters of the HIST-ETAS model. I thank T. Okazaki for providing strain rate data (Fukahata et al., 2022).