Application of an Objective Detection Method of Long-Term Slow Slip Events using GNSS Data: Detection of Short-Term Slow Slip Events and Estimation of Moment Magnitude of Long-Term Slow Slip Events

Abstract

Long-term and short-term slow slip events (SSEs) have occurred repeatedly in the Nankai Trough subduction zone, Japan. The SSEs may incrementally stress the adjacent parts of the locked megathrust zone. When SSEs occur, it is important to determine whether they are similar to previous repeated events, in order to judge whether the probability of occurrence of a large Nankai Trough earthquake is relatively high. In this study, we objectively detected short-term SSEs in the Nankai Trough subduction zone by correlating the GNSS daily and 6-hour coordinates with a ramp function with a one-week slope, excluding common noise and long-term trends. The spatiotemporal distribution of short-term SSEs detected was in good agreement with the occurrence of deep low-frequency earthquakes. In addition, assuming slip on a rectangular fault on a plate boundary, we estimated the moment magnitude of long-term SSEs from displacement data for two years and obtained results that were close to those of previous studies.