Japan Geoscience Union Meeting 2023

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-CG Complex & General

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

Thu. May 25, 2023 10:45 AM - 12:15 PM International Conference Room (IC) (International Conference Hall, Makuhari Messe)

convener:Aitaro Kato(Earthquake Research Institute, the University of Tokyo), Asuka Yamaguchi(Atomosphere and Ocean Research Institute, The University of Tokyo), Yohei Hamada(Japan Agency for Marine-Earth Science and Technology Kochi Institute for Core Sample Research), Yihe Huang(University of Michigan Ann Arbor), Chairperson:Takanori Matsuzawa(National Research Institute for Earth Science and Disaster Resilience), Kurama Okubo(National Research Institute for Earth Science and Disaster Resilience)

12:00 PM - 12:15 PM

[SCG45-21] Single-station detection of seismic slow earthquakes using their broadband characteristics

*Koki Masuda1, Satoshi Ide1 (1.Department of Earth an Planetary Science, University of Tokyo)


Keywords:slow earthquakes, broadband slow earthquakes, tectonic tremor, very-low-frequency earthquake, Nankai subduction zone, Mexico

Slow earthquakes radiate tiny signals and are observed only in some limited frequency bands with low noise. Those observed in 1-10 Hz are called tectonic tremors or low-frequency earthquakes and those observed in 0.01-0.05 Hz are called very-low-frequency earthquakes (VLFE). These seismic slow earthquakes are spatiotemporally correlated, and the seismic-moment rate calculated from VLFE is almost always proportional to the seismic-energy rate calculated in the tremor frequency band (Ide et al., 2008). Brownian motion-type models (e.g., Ide, 2008) can explain this relationship and also have predicted the radiation of broadband signals through 0.01-10 Hz. In fact, broadband detections of seismic slow earthquakes including microseism frequency of 0.05-1 Hz support the idea (e.g., Kaneko et al., 2018; Masuda et al., 2020). In this study, we utilize this characteristic of slow earthquakes to design a method to monitor slow-earthquake activities even from a single-station data.

From a broadband seismogram recorded at a single station, we measure seismic energy rate as the squared-velocity waveform in 2-8 Hz and, and seismic moment rate as the displacement waveform in 0.02-0.05 Hz. Then we calculate the correlation coefficient between the seismic energy rate and seismic moment rate, every 10 s in a time window of 100 s, and take a moving average of 10000 s. We regard the timing when this value exceeds a certain threshold is “detection”.

The first application of this method is to the continuous records of F-net, a broadband seismic network of 75 stations in Japan for 18 years. The detected activities are spatiotemporally consistent with a tremor catalog (Mizuno and Ide, 2019), and the false-positive rate is low. Though some tremor activities, especially far from the station, are missed, this limitation of the detectable distance constrains the locations of detected seismic slow earthquake activities. Next, we apply this method to the Guerrero, Oaxaca, and Jalisco regions in the Mexican subduction zone. In the Guerrero and Oaxaca regions, we expand the number of usable stations as well as obtain detections consistent with a previous study (Husker et al., 2019). Furthermore, in the Jalisco region, this is the first long-term analysis of seismic slow earthquakes using a permanent station, and the large-scale activities detected by this study are not only consistent with previous a geodetic study but also newly detected one.