Long-term slow slip event detected beneath the Shima Peninsula, central Japan, from GNSS data

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.