4:30 PM - 4:45 PM
[SSS30-21] Estimation of Radiated Seismic Energy of Repeating Earthquakes in Northeastern Japan and its Spatio-Temporal Variation
The target earthquakes of this study are 160 repeating earthquakes detected by Uchida and Matsuzawa . These earthquakes are divided into 52 repeating earthquake groups. Seismic activity of these events extends before and after the Tohoku-Oki earthquake and includes groups that showed enlarged magnitude and shortened inter-event time after the earthquake as represented by Kamaishi sequence. To estimate radiated seismic energy, we use the method for measuring amplitude developed by Mayeda et al.  and the method for estimating source spectra and radiated seismic energy developed by Baltay et al.  with slight modifications. In this modification, we linearized the calculation to quantitatively estimate the error of the radiated seismic energy that has not been discussed precisely.
We obtained a positive depth dependency of scaled energy, the ratio between radiated seismic energy and seismic moment, as a main characteristic of spatial variation. This is consistent with the results in previous studies. We also observe some temporal changes in scaled energy. For Kamaishi-sequence, the scaled energy decreased suddenly after the Tohoku-Oki earthquake and gradually recovered, coinciding with a sudden increase and gradual decay of seismic moment. This temporal change of seismic moment has been interpreted as the expansion of rupture into conditionally stable region around the unstable region [Uchida et al., 2015]. The temporal change of scaled energy suggests that the ratio of fracture energy is larger in this conditionally stable region.
Radiated seismic energy is related to the strength of the fault, which increases after an earthquake. Therefore, we expect some correlation between the inter-event time and scaling energy for repeating earthquakes. In our result, there are several groups and regions that have positive dependency of scaled energy on the inter-event time, but this relation cannot be confirmed generally.