Additional file 1 of Seismic observation using distributed acoustic sensing around the Tsugaru Strait at the Japan and Kuril Trenches, northeastern Japan
Creators: name: Baba, Satoru
name: Araki, Eiichiro
name: Yokobiki, Takashi
name: Kawamata, Kei
name: Uchiyama, Keisuke
name: Yoshizuka, Takuji
Publisher: name: figshare
Year: 2024
Subjects: subject: Geophysics
subject: FOS: Earth and related environmental sciences

description: Additional file 1: Text S1. Trial of STA/LTA method. Text S2. Trial of direct fit of the relationship between DAS amplitude, magnitude, and hypocentral distance. Figure S1. Distribution of earthquake epicenters listed in the earthquake catalog of the Japan Meteorological Agency (JMA) around the Tsugaru Strait from April 1, 2022, to March, 2023. Dashed contours indicate the isodepths at the top of the subducting Pacific plate at 25 km intervals (Nakajima and Hasegawa 2006; Kita et al. 2010). The red line represents the fiber-optic cable for distributed acoustic sensing (DAS) measurement. Figure S2. Distribution of epicenters of earthquakes listed in the JMA earthquake catalog and detected by a visual inspection and b STA/LTA method. The red line represents the fiber-optic cable. Black lines are trenches. Figure S3. Time–distance plot of strain rate data from DAS measurements at 2–10 Hz when events that were found visually but cannot be detected by STA/LTA method occurred. Hypocenters, origin times in UT, and magnitudes of earthquakes were based on the JMA earthquake catalog. Figure S4. Time–distance plot of strain rate data from DAS measurements at 2–10 Hz when falsely detected by STA/LTA method. Figure S5. Time–distance plot of strain rate data from DAS measurements at 2–10 Hz (a–d, f) or 0.01–0.1 Hz (e) when an event occurred. Hypocenters, origin times in UT, and magnitudes of earthquakes were based on the JMA earthquake catalog (a, c, d) or the United States Geological Survey earthquake catalog (e). Figure S6. Time–distance plot of strain rate waveform a near the northern and b southern coastlines. Figure S7. Station correction factors used for event location based on hypomh (Hirata and Matsu’ura 1987). These factors were added to the observed arrival times of P-wave and S-wave. Figure S8. Estimated site amplification factors for each channel. Figure S9. Examples of the relationship between the site-corrected DAS amplitude A (nstrain/s) and hypocentral distance r (km) for some events. The dashed lines in a and b represent the regression lines between A and r. Figure S10. a Relationship between the acceleration amplitudes at A.TSRN (140.8915ºE, 41.7736ºN) and A.HRDA (140.8810ºE, 41.4488ºN), managed by the Association for the Development of Earthquake Prediction, and the hypocentral distance for all events. Different combinations of colors and shapes indicate different events. b Same as (a), but the acceleration amplitude was calibrated to M 1. The dashed line represents the regression line between acceleration amplitude Aacc (nm/s2) and hypocentral distance r (km). Table S1. Location of earthquakes analyzed in this study. The lines with JMA and DAS are locations located by JMA and by this study, respectively. Table S2. Information in earthquakes used for the discussion of DAS amplitudes in “Discussion of DAS amplitudes” section. Origin times and locations are based on the JMA catalog. Table S3. Calculated parameters of the regression line between a logarithm of the hypocentral distance r (km) and a logarithm of the site-corrected DAS amplitude A (nstrain/s) derived for each event using the least-squares method. The relationship between r and A was fitted by log10A=a log10r+b. List of a and b for each event is shown.