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Keywords:

  • slow slip event;
  • automated detection;
  • slow earthquake

[1] We have developed a new automated method for the identification and location of slow slip events (SSEs) during episodic tremor and slip (ETS) in the Nankai subduction zone without any tremor information. SSE models are estimated from continuous tilt data using the Kalman filter algorithm and a grid search, and are eventually identified through statistical evaluations. We applied this method to data recorded for two years in Shikoku, Japan and successfully detected four SSEs coincident with major tremor bursts. Before the onset of SSEs, precursory minor tremor activities usually occur around the fault where SSEs are subsequently detected when tremor migrates into the SSE faults. This suggests that an ETS episode begins with geodetically undetectable small slip around the main fault and grows to a detectable SSE. Such evolution of SSE and tremor activity would reflect the spatial change in the slip property on the plate interface.