Slow slip events in the Kanto and Tokai regions of central Japan
detected using GNSS data during 1994-2020
Abstract
Slow slip events (SSEs) along subduction zones play an important role in
accommodating relative plate motion. SSEs interplay with large
megathrust earthquakes and other slow earthquakes, including low
frequency and very low frequency earthquakes. The Kanto and Tokai
regions of central Japan host frequent slow and large earthquakes, with
significant differences in slip behavior along the subduction zones in
the Suruga Trough, Sagami Trough, and Japan Trench. In this study, we
conducted a systematic search to estimate the fault models and durations
of short-term SSEs using continuous Global Navigation Satellite System
(GNSS) data collected from 1994 to 2020. We detected 179 potential SSEs
with moment magnitudes of 5.3–7.0 and durations of 0–80 days from the
time series. Along the Sagami Trough, two shallow regions at a depth of
10–20 km host Mw ≥ 6.5 SSEs off of the Boso Peninsula
and accommodate most of the relative plate motion aseismically. Some
SSEs also occur on the deep plate interface down to ~50
km without low frequency tremors (LFTs). Along the Japan Trench, the
cumulative slip of the SSEs exhibits a bi-modal depth distribution to
avoid the large slip areas of past megathrust earthquakes at 30–40 km
depth. The shallow SSEs are in the same depth range (10–30 km) as LFTs,
but are spatially separate from LFTs along the trench. The detected SSEs
have limited temporal correlations with other slow earthquakes and
earthquake swarms, which suggests that many factors control the genesis
of slow and regular earthquakes.