[S-CG44] Science of slow-to-fast earthquakes

[SCG44-P22] Estimation of the crustal deformation using radiated energy of tectonic tremors

*Tsukasa Yamamoto¹, Yoshihiro Hiramatsu² (1.Kanazawa University Graduate School Of Natural Science and Technology, 2.Kanazawa University Institute of Science and Engineering Faculty of Geosciences and civil Engineering)

Keywords:tectonic tremors, slow slip event

Monitoring of slip on the transition zone on the plate interface of a subducting plate is important in considering the seismogenic process in its shallow part. The accumulated radiated energy of tectonic tremors (hereinafter referred to as tremors) during ETS events is known to be a good indicator of the amount of crustal deformation in short-term SSEs (Maeda and Obara, 2009). The spatial distribution of radiated energy reveals the existence of tremor asperities, suggesting their contribution to the spatiotemporal evolution of slow earthquakes (Ghosh et al., 2012; Nakamoto et al., 2021). It has also been reported that the strain rate is proportional to the tremor amplitude (Hawthorne and Rubin, 2013). On the other hand, there have been slow slips without tremors (Wech and Bartlow, 2014). Thus, the possibility of estimating the amount of slip using tremors has remained unclear. The purpose of this study is to estimate the crustal deformation from the radiated energy of tremors beneath the northern part of the Kii Peninsula, where the source location and radiated energy of tremors have been determined in detail (Nakamoto et al., 2021).
The data used in this study are the hypocenters and radiated energy of tremors reported by Nakamoto et al. (2021). They analyzed seismic waveform data from the array observation of the National Institute of Advanced Industrial Science and Technology (AIST). We set sub-faults of 10 km square on the plate interface beneath the Kii Peninsula and calculated the amount of crustal deformation at the ground surface by estimating the amount of slip from the radiated energy of tremors at each fault. For the conversion from radiated energy to seismic moment, we used a constant value of 7.0×10^-10J/Nm, which is the typical value for the northern Kii Peninsula among the scaled energy estimated by Ide and Yabe (2014).
We estimated temporal changes in crustal deformation by distributing tremors to the sub-faults every hour. The temporal tilt changes estimated from tremors show a good fit with those caused by short-term SSEs within several factors of magnitude. The scaled energy estimated by Ide and Yabe (2014) is in the range of 3×10^-10-10^-9. Applying an appropriate value of the conversion may reproduce the tilt changes of short-term SSEs.