Long-term Slow Slip Event around Kochi City from 1977 to 1980

Abstract

We extracted unsteady vertical crustal deformations in the Shikoku region before GPS deployment using leveling and sea-level 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. Monthly mean sea-level data were corrected for atmospheric pressure and hydrographic effects. As a result, we found an upheaval of 4-5cm near Kochi City from 1977 to 1980 in both the leveling and sea-level data. This may represent a crustal deformation caused by a long-term slow slip event on the plate boundary.