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

Tae-Kyung Hong,Seongjun Park,Woohan Kim,Junhyung Lee

doi:10.1038/s41598-018-31600-5

Tae-Kyung Hong, Seongjun Park + Show 2 more

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https://doi.org/10.1038/s41598-018-31600-5

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Abstract

The distance-dependent coseismic and postseismic displacements produced by the 2011 MW9.0 Tohoku-Oki megathrust earthquake caused medium weakening and stress perturbation in the crust around the Korean Peninsula, increasing the seismicity with successive ML5-level earthquakes at the outskirts of high seismicity regions. The average ML5-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 ML5-level midcrustal earthquakes additionally changed the stress field in adjacent regions, inducing the 15 November 2017 ML5.4 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.

Highlights

The distance-dependent displacements produced tension stress over the Korea Peninsula[11] (Fig. 1), and the discriminative crustal extension decreased the seismic velocity in the crust[12,16,17,18,19]
We investigate the properties of the successive ML5-level earthquakes and their induction mechanisms on the Korean Peninsula
The seismic velocities in the crust of the Korean Peninsula decreased by ~3% instantly after the 2011 Tohoku-Oki megathrust earthquake[12]

Summary

Introduction

The megathrust earthquake incorporated large lithospheric displacements up to regional distances[10,11,12]. The 2011 Tohoku-Oki megathrust earthquake produced coseismic displacements of ~4 cm around the east coast and ~2 cm around the west coast of the Korean Peninsula (Fig. 1)[11,13,14]. The distance-dependent displacements produced tension stress over the Korea Peninsula[11] (Fig. 1), and the discriminative crustal extension decreased the seismic velocity in the crust[12,16,17,18,19]. The seismicity increase may have been caused by the decreasing yield strength of the medium due to instantaneous activation of the tension field by crustal extension[11]. It was suggested that a small change in stress field may induce significant www.nature.com/scientificreports/

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