[S12-P] Poster

[S12-P-02] Precursory signature of a megathrust earthquake and postseismic effects on regional earthquake induction

^○Tae-Kyung Hong, Junhyung Lee, Seongjun Park (Yonsei University, Seoul, South Korea)

The prediction of great earthquakes has not been
successful despite various efforts. Finding a signature
for impending great earthquakes is crucial for seismic
hazard mitigation. We observed a temporal change of the
Gutenberg-Richter frequency-magnitude relationship (b
value) before the 2011 Tohoku-Oki megathrust earthquake
for more than 20 years. It is observed that the b values
decrease with time before the events. The change of b
value of region is proportional to the cumulated stress.
The megathrust earthquake caused large permanent
lithospheric displacements in regional distances. The
seismicity around the Korean Peninsula was increased
significantly after the 2011 M9.0 Tohoku-Oki earthquake,
which is not consistent with the expected
seismic-quiescence. Strong seismic waves cause large
dynamic stress changes, incurring fluid migration and
increasing pore fluid pressure in the media. The
lithospheric displacements directing to the epicenter on
the convergent plate boundary develop transient radial
tension field over the backarc lithospheres. The seismic
velocities in the lithosphere changed abruptly up to 2 %
after the megathrust earthquake, which recovered
gradually with time for several years. The ambient stress
field is recovered gradually as the induced stress field
diminishes with time by tectonic loading. A series of
moderate-size earthquakes and earthquake swarms occur as
a consequence of medium response to the temporal
evolution of stress field. The long-term evolution of
seismicity is expected to continue until the ambient
stress field is fully recovered.