Correlation of Seismicity With Faults in the South Korea Plateau in the East Sea (Japan Sea) and Seismic Hazard Assessment

Han-Joon Kim,Seonghoon Moon,Hyeong-Tae Jou,Bo Yeon Yi,Kwang-Hee Kim

doi:10.3389/feart.2022.802052

Abstract

The South Korea Plateau (SKP) is a structural high at the eastern continental margin of the Korean Peninsula. Earthquakes occur frequently in the SKP although they are not larger than ML5.0 in magnitude. The SKP is a region of highly rifted continental crust engraved with rifts created during back-arc rifting in the NW Pacific subduction zone that led to the separation of the SW Japan Arc in the Cenozoic. The Bandal, Onnuri, and Okgye Rifts are well-defined rifts in the SKP. Multichannel seismic profiles show that the rifts in the SKP are bounded by large-offset normal faults and their subsided basement is deformed by domino-style faulting. A close spatial correlation is recognized between the epicentral locations of earthquakes with relatively large magnitude and the rift-bounding fault of the Onnuri Rift. The faults in the SKP is interpreted to be reactivated with strike-slip since the middle Miocene. The maximum expected magnitude of earthquakes (Mmax) computed statistically using the catalog including instrumentally recorded seismicity is ML5.42. However, Mmax estimated from the catalog including instrumentally recorded seismicity and historical records increases to ML6.67.

Highlights

The separation of the SW Japan Arc from the Korean Peninsula proceeded with back-arc rifting and spreading that created the East Sea (Japan Sea), a back-arc sea behind the Japan Arc in the NW Pacific subduction zone (Figure 1)
Earthquakes occur frequently in the South Korea Plateau (SKP), as recorded officially since 1 March 1982 by the Korea Meteorological Administration, their magnitudes are less than ML 5.0 (Figure 2)
The faults displacing the basement in the SKP are identified on seismic profiles (Figures 5–7)

Summary

Introduction

The separation of the SW Japan Arc from (near) the Korean Peninsula proceeded with back-arc rifting and spreading that created the East Sea (Japan Sea), a back-arc sea behind the Japan Arc in the NW Pacific subduction zone (Figure 1). The South Korea Plateau (SKP) is a dominant topographic feature at the present continental margin of the middle Korean Peninsula. The SKP is further divided into the eastern and western blocks termed the ESKP and the WSKP, respectively (Figure 2). Earthquakes occur frequently in the SKP, as recorded officially since 1 March 1982 by the Korea Meteorological Administration, their magnitudes are less than ML 5.0 (Figure 2). A noticeable increase in the number of events in recent years is recognized (Figure 3). The average annual number of events before year 2017 is 1.1; in contrast, the average number since

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