Long-Term Evolution of Intraplate Seismicity in Regional Distance After Megathrust Earthquake

Monday, 15 December 2014
Tae-Kyung Hong, Soung Eil Houng and Junhyung Lee, Yonsei University, Seoul, South Korea
It has been poorly understood how the regional intraplate seismicity evolve with time after megathrust earthquakes. Also, it is unknown whether the great earthquakes will induce hazardous earthquakes in regional intraplate regions. We investigate the seismicity property changes around the Korean Peninsula before and after the 2011 Tohoku-Oki earthquake. The long-term response of media for the great earthquake and potential seismic hazards in intraplate regions are discussed. The megathrust produces large lithospheric displacements up to regional distances, constructing transient tensional stress fields in the backarc lithospheres around the Korean Peninsula. These additional stress fields cause decreases of Coulomb failure stresses and increase the seismicity in optimally-oriented strike-slip or normal faults. The transient stress perturbation diminishes with time by lithostatic loading, making gradual recovery of the ambient stress field. The seismicity evolves with the stress change. The long-term evolution of regional intraplate seismicity in regional intraplate regions with negative Coulomb stress changes is poorly understood. Strong seismic waves from the great earthquake produce dynamic stress changes in local and regional distances, increasing pore fluid pressure in fluid-including medium. The radial tension field and pore pressure increase induces abrupt increase of seismicity with intact-medium faulting. A series of moderate-size earthquakes and earthquake clusters develop 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 preseismic ambient stress field is fully recovered.