Kinematic Rupture Characterization of Large Compressional Intraslab
Earthquakes Along the Tohoku Region, Japan
Abstract
We examine the source parameters of four Mw≥7.0 intraslab earthquakes
that occurred near the Tohoku coast over the past two decades: 2003,
2011, 2021, and 2022. By analyzing the finite fault slip histories
constrained by inland strong motion observations, we found that these
earthquakes occurred within the upper plane of the subducted Pacific
Plate due to downdip compression caused by plate unbending. These
earthquakes have a more compact fault area and higher stress drop
compared to shallow crustal earthquakes. Additionally, intraslab
earthquakes have much slower relative rupture velocity than shallow
crustal earthquakes. Good spatial correlations between the static stress
drop and slip rate are found, which may suggest the compatibility
between dynamic stress drop and static stress drop. The rupture area,
average slip, asperity area, average static stress drop over the entire
fault, and asperities are consistent with the reported scaling
relationship for global intraslab earthquakes within a similar depth
range. Using plate unbending, we found the recurrence intervals of these
intraslab earthquakes are around 600 years, which is comparable with
that of the 2011 Tohoku earthquake. A visual spatial-correlation between
the locations of these earthquakes and seismicity in the lower plane is
reported. These findings provide insights into the tectonic background
and source parameters of intraslab earthquakes in the Tohoku region and
contribute to better seismic hazard assessment.