Imaging tectonic tremor in Japan using an automatic tool for detection and location

What is it about?

In this study, we analyze through the BackTrackBB method a particularly energetic sequence of tectonic tremor and low-frequency earthquakes (LFEs) lasting 9 days, occurring at the base of the Nankai subduction interface in southwest Japan. The application of BackTrackBB allows us to extract a more complete and resolved low-frequency earthquake catalog (approximately 6.5 times more events) than the routine catalog provided by the Japan Meteorological Agency (JMA). This catalog reveals in detail the spatio-temporal evolution of LFE activity, highlighting spatial and temporal clustering, modulations in response to tides, and patterns of spatio-temporal migration at different scales. In the second part of the study, we detect and locate longer-duration energy transients (tectonic tremor) using characteristic functions constructed from smoothed energy envelopes. The spatial probability map of tectonic tremor shows a segmentation along the strike equivalent to that highlighted by the analysis of LFE activity: LFEs coincide in space with the sources of tectonic tremor. This observation provides a potential constraint on the size of the source region of tectonic tremor. This study illustrates the contribution of statistical methods based on signal coherence across a network, such as BackTrackBB, to detect and monitor the different components of tectonic tremor activity. It thus opens new perspectives for understanding the underlying mechanisms of slow earthquake generation.

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