LAUSR

Slow slip events (SSEs) regularly occur near the Boso Peninsula, central Japan. Their time of recurrence has been decreasing from 6.4 to 2.2 years from 1996 to 2014. It is important to better constrain the slip history of this area, especially as models show that the recurrence intervals could become shorter prior to the occurrence of a large interplate earthquake nearby. We analyze the seismic waveforms of more than 2,900 events (M ≥ 1.0) taking place in the Boso Peninsula, Japan, from 1 April 2004 to 4 November 2015, calculating the correlation and the coherence between each pair of events in order to define groups of repeating earthquakes. The cumulative number of repeating earthquakes suggests the existence of two slow slip events that have escaped detection so far. Small transient displacements observed in the time series of nearby GPS stations confirm these results. The detection scheme coupling repeating earthquakes and GPS analysis allow to detect small SSEs that were not seen before by classical methods. This work brings new information on the diversity of SSEs and demonstrates that the SSEs in Boso area present a more complex history than previously considered.