[S-CG45] Science of slow-to-fast earthquakes

[SCG45-P18] Quantitative relationship between deep low-frequency tremor and short-term slow slip events beneath the Kii Peninsula

*Akemi Noda¹, Kenichi Fujita¹, Yasutaka Yamana¹, Tomoaki Masuda¹ (1.Seismology and Volcanology Department, Japan Meteorological Agency)

Keywords:Deep low-frequency tremor, Deep low-frequency earthquake, Short-term slow slip event, Kii peninsula

Slow earthquakes in the deep extension of the source region of large interplate earthquakes along the Nankai Trough, including deep low-frequency earthquakes (LFEs) and tremor, very low frequency earthquakes, and short-term and long-term slow slip events (SSEs), are associated with slip phenomena on the plate boundary. Therefore, information on the spatiotemporal distribution and magnitude of these slow earthquakes is expected to serve as clues for evaluating changes in frictional state at the plate boundary and stress loading onto the source region, leading to the next large interplate earthquake. The occurrence periods and locations of LFEs and tremor and short-term SSEs approximately correspond (e.g., Obara, 2002; Rogers & Dragert, 2003), and they are interpreted as observations of the same slip phenomenon on the plate boundary in different frequency bands. It has been reported that there is a correlation between the seismic moment or duration of LFEs/tremor and the seismic moment of short-term SSEs (Hiramatsu et al. 2008; Aguiar et al., 2009; Daiku et al., 2018; Frank & Brodsky, 2019). Thus, it is expected that smaller-scale SSEs than those currently detectable by geodetic data can be resolved through seismic observations. This study investigates the relationship between LFEs/tremor and short-term SSEs quantitatively, based on abundant observational data, with the future goal of implementing high-resolution monitoring of slip phenomena at the plate boundary along the Nankai Trough.
To monitor the interplate coupling in the Nankai trough subduction zone, the Japan Meteorological Agency (JMA) has been cataloging fault models of short-term SSEs estimated from strainmeter and tiltmeter data during the occurrence of the short-term SSEs. From 2011 to the present, over 250 fault models of short-term SSEs have been estimated and divided into several activity areas based on the locations of fault and characteristics of crustal deformation to aid in monitoring (Fujita et al., 2023 SSJ Fall Meeting). We estimate the occurrence periods, source locations, and radiated energy of LFEs/tremor which occurred synchronously with the cataloged short-term SSEs and statistically investigate the spatiotemporal and magnitude correlations with the fault models of short-term SSEs. For low-frequency tremor, we estimate the tremor sources from Hi-net data provided by the National Research Institute for Earth Science and Disaster Resilience (NIED) using the envelope correlation method. We then calculate the radiated energy from the tremor by correcting for the geometric spreading and the effects of scattering and anelastic attenuation from the seismic wave amplitudes. For LFEs, we use the hypocenter and magnitude of LFEs listed in the JMA Unified Earthquake Catalog. We demonstrate the relationship between the short-term SSEs and LFEs/tremor that occurred beneath the Kii Peninsula and discuss its variability and regional characteristics.

Acknowledgments:
For the analysis of short-term SSEs, we used strainmeter data from the JMA and Shizuoka Prefecture. We also used strainmeter and tiltmeter data from the National Institute of Advanced Industrial Science and Technology (AIST). For the analysis of deep low-frequency tremor, we used Hi-net data from the NIED.