Disaster mitigation

[DM-07] Estimation of the seismogenic layer in the source region of the 2008 Iwate-Miyagi Nairiku earthquake based on the redetermination of source distribution by using Hi-net data

*Takanobu Sato¹, Hiroaki Sato¹ (1. Central Research Institute of Electric Power Industry (Japan))

The depths of the upper and lower limits of the seismogenic layer are important for the evaluation of earthquake ground motions because this information provides the basis for the size and depth of the source fault model. However, since the seismogenic layer is deeper than the seismic basement in the uppermost crust, it is difficult to investigate using geophysical exploration. Therefore, the seismic layer is identified not only by the seismic wave velocity structure but also by using the source distribution of small earthquakes by the JMA earthquake catalog. In estimating the lower limit depth of the seismogenic layer, information such as the Conrad depth and the Curie point depth is also used.
During the 2008 Iwate-Miyagi Nairiku earthquake (Mj 7.2), extremely large acceleration records were recorded at near-source fault, and it is suggested that the seismogenic layer is estimated to be shallower than the JMA earthquake catalog based on the aftershock distribution determined from the dense earthquake observations. In this study, to improve the accuracy of the source distribution by using Hi-net data by NIED, which can be used uniformly nationwide in Japan, we redetermine the source distribution of the 2008 Iwate-Miyagi Nairiku earthquake source region. Specifically, we will apply the homogeneous station method, which uses the same observation station pairs for all earthquakes to determine the seismic source location and avoids bias in the seismic source distribution due to the different station pairs. In addition, the double-difference method, which can accurately determine the relative seismic source location when the seismic source region is limited, is also applied to determine the accurate seismic source distribution. Furthermore, we will also discuss the effect of the assumed velocity structure model used in the source location determination on the estimated seismic source distribution.