Repetitive long‐term slow slip events beneath the Bungo Channel, southwestern Japan, identified from leveling and sea level data from 1979 to 2008

Leveling and sea level data for the period from 1979 to 2008 around the Bungo Channel, southwestern Japan, were investigated to characterize vertical deformation patterns. We found evidence of discrete events that may have occurred beneath the Bungo Channel before the two most recent long‐term slow slip events (SSEs) (1996–1997 and 2003) detected from GPS data. GPS‐derived steady state vertical displacements related to ongoing subduction of the Philippine Sea plate were subtracted from the vertical displacements observed by leveling surveys. The spatial pattern of the residual vertical displacements observed by leveling was similar to that observed by GPS in the periods including recent long‐term SSEs. This suggests that discrete vertical displacements, which might represent long‐term SSEs, have occurred in each of four intervals between leveling surveys before GPS deployment. We calculated differences of sea level between tidal stations near the Bungo Channel after some corrections and then cross‐correlated them with the GPS‐derived vertical displacements of the recent long‐term SSE to estimate the timing of the events. These cross correlations and the discrete vertical displacements derived from leveling suggest that long‐term SSEs may have occurred around 1980, around 1985–1986, and around 1991.