Abstract
Long-term slow slip events (SSEs), the largest events among slow earthquakes, occur repeatedly along the Nankai Trough, southwest Japan. Their locations, near the locked zones of the plate interface responsible for great megathrust earthquakes in the Nankai Trough, suggest that these events influence conditions in this critical seismogenic region. Characterizing the spatiotemporal changes of long-term SSEs is important for understanding changes in the locked portions of the plate interface before major earthquakes. Two decades of observations by the global navigation satellite system along the Nankai Trough have detected no long-term SSEs in a large area beneath the Kii Peninsula. We report details of a long-term SSE detected in satellite navigation data from the Shima Peninsula, the easternmost part of the Kii Peninsula, from spring 2017 to autumn 2018. The estimated moment release from this event is equivalent to an earthquake of magnitude 6.4.
Highlights
Slow earthquakes are typically observed in the transition zones between locked and creeping zones on plate boundaries (Obara and Kato 2016)
This paper reports a small long-term slow slip event (SSE) that occurred beneath the Shima Peninsula during 2017 and 2018, the first detection of such an event from global navigation satellite system (GNSS) data
High correlation related to 2000 Tokai long-term SSE extended to the Shima Peninsula
Summary
Slow earthquakes are typically observed in the transition zones between locked and creeping zones on plate boundaries (Obara and Kato 2016). Long-term slow slip events (SSEs), with durations of months or years, have been observed by using data from the global navigation satellite system (GNSS) in the Bungo Channel (Hirose et al 1999), the Kii Channel (Kobayashi 2014), and the Tokai region (Ozawa et al 2002) (see Fig. 1 for locations). Kobayashi (2017) used GNSS observations to objectively detect long-term SSEs along the Nankai Trough and reported that they are not distributed homogeneously along the strike direction.
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