Time-advanced occurrence of moderate-size earthquakes in a stable intraplate region after a megathrust earthquake and their seismic properties

摘要

The distance-dependent coseismic and postseismic displacements produced by the 2011 M _W 9.0 Tohoku-Oki megathrust earthquake caused medium weakening and stress perturbation in the crust around the Korean Peninsula, increasing the seismicity with successive M _L 5-level earthquakes at the outskirts of high seismicity regions. The average M _L 5-level occurrence rate prior to the megathrust earthquake was 0.15?yr?1 (0.05–0.35?yr?1 at a 95% confidence level), and the rate has increased to 0.71?yr?1 (0.23–1.67?yr?1 at a 95% confidence level) since the megathrust earthquake. The 2016 M _L 5-level midcrustal earthquakes additionally changed the stress field in adjacent regions, inducing the 15 November 2017 M _L 5.4 earthquake. The successive 2016 and 2017 moderate-size earthquakes built complex stress fields in the southeastern Korean Peninsula, increasing the seismic hazard risks in the regions of long-term stress accumulation. The increased seismic risks may continue until the medium properties and stress field are recovered.