Mechanically coupling on the plate interface in the Nankai trough, Japan
and a possible seismic and aseismic rupture scenario for megathrust
earthquakes
Abstract
Quantifying the stress distribution or finding mechanically coupled
areas on the plate interface is fundamentally important for conjecturing
megathrust earthquakes that may occur in the future. Kinematically
coupled areas, or slip deficit distributions, on plate interfaces were
commonly estimated by geodetic-data analyses. However, mechanically
coupled areas are not identical to the kinematically coupled areas. The
present study develops an inversion method to estimate thestress rate
distribution as mechanically coupled areas. We apply this method to the
Nankai trough subduction zone, southwestern Japan to detect mechanically
coupled areas. Some of the estimated coupled areas correspond to the
rupture areas of historical earthquakes. Others are in a deeper part,
which may release the stress as aseismic slip. We then construct a
rupture scenario that can occur in the Nankai trough in the future based
on the estimated mechanical coupling,assuming that an effective stress
accumulation period is 100 years. The scenario consists of a foreshock
of MW 8.0 followed by an afterslip of
MW 7.9 and a mainshock of
MW 8.2. Although the moment magnitude of the
afterslip is similar to the foreshock, the energy released by the
foreshock is significantly larger than the afterslip because the stress
drop of the afterslip is small.