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Comparison of Multiple Methods to Identify Remotely Triggered Tremor and Their Application in Japan Following the 2024 M 7.5 Noto Earthquake

Description: 

Deep tectonic tremor belongs to seismically observed slow earthquakes. It is found beneath the seismogenic zone along major plate boundary faults. While most tremor occurs spontaneously or is driven by aseismic slow-slip events (ambient tremor), tremor can be dynamically triggered during long-period surface waves of large distant earthquakes (triggered tremor). The most common way to identify triggered tremor is through a visual inspection of spectrograms or high-frequency waveforms modulated by the surface waves, which is time-consuming and subjective. Recently several automatic methods like cross-correlation of long-period seismic waves and high-frequency envelope function for ambient tremor detection (Masuda and Ide, 2023), or energy ratios between the triggering and preceding windows for dynamic triggering (Yun et al., 2021), have been developed. In this study, we compared the performance of these automatic methods with the results from the visual inspection. We utilized continuous waveforms recorded by Hi-net and F-net stations in Japan (epicentral distance > 200 km) following the 2024 M7.5 Noto Hanto earthquake. Our visual inspection found triggered tremor in Shikoku and Kyushu regions, consistent with previous findings (Chao and Obara, 2016). In addition, we found a prolonged increase of low-frequency earthquakes in the Kii Peninsula, likely driven by a slow-slip event delay triggered by the Noto mainshock. Next, we computed the cross-correlation coefficients (CCCs) between high-frequency envelope functions and long-period surface waves, using them as metrics to quantify the triggering relationship. While the CCCs show relatively high values at stations where triggered tremor is visually identified, we also found high values at stations with strong clipping or triggered earthquakes/aftershock signals. Our next step is to combine the CCCs values with other parameters to come up with a robust automatic way to identify triggered tremors following large distant earthquakes. We will also combine with other geodetic observations to understand candidate mechanisms for increasing low-frequency earthquakes.

Session: The 2024 Magnitude 7.5 Earthquake and the Associated Earthquake Swarm Beneath the Noto Peninsula, Central Japan [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Chang

Student Presenter: Yes

Invited Presentation: 

Authors