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

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 ML 5.0 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 ML 5.42. However, Mmax estimated from the catalog including instrumentally recorded seismicity and historical records increases to ML 6.67.

Seismic stratigraphy and structural evolution of the South Korea Plateau, East Sea (Sea of Japan)

“…The SKP formed by extension was associated with back‐arc rifting in the NW Pacific subduction zone and separation of the southwestern Japan since Late Oligocene time (Kim, Lee, Choi, et al, 2015; Kim, Lee, Park, et al, 2015, Kim et al, 2022; Tamaki et al, 1992). At the time, the plateau was extended through domino‐style block faulting, resulting in rapid tectonic subsidence along the fault planes (Figure 14a).…”

“…Since the early 2000s, the SKP has attracted attention in terms of gas‐hydrate exploration, and extensive two‐dimensional (2D), multi‐channel, seismic data were acquired by the Korea Institute of Geoscience and Mineral Resources (KIGAM) between 2000 and 2004 (Figure 1c). Based on these geophysical data, numerous studies have been carried out in the fields of seismic stratigraphy (Cukur et al, 2015, 2018; Horozal et al, 2017; Kwon et al, 2009), structural evolution (Chough et al, 2018; Kim et al, 2007; Kim, Lee, Choi, et al, 2015; Kim, Lee, Park, et al, 2015), volcano‐tectonic evolution (Kim et al, 2011) and geo‐hazard assessment (Cukur et al, 2018; Kim et al, 2022). Moreover, the Integrated Ocean Drilling Program (IODP) Expedition 346, which collected data at Site U1430 in the Eastern South Korea Plateau (ESKP), played an important role in enhancing our understanding of palaeoclimatic and palaeoceanographic variability (Kim et al, 2019; Kim, Yi, et al, 2020; Kim, Yoo, et al, 2020).…”

“…Because the formation of a tectonostratigraphic unit is mainly controlled by basin‐forming tectonism, a tectonostratigraphic unit provides valuable information about basin evolution processes and regional basin‐infill history (Roberts & Bally, 2012). The SKP is composed of several rift basins (half‐grabens), including the Bandal (BB), Okgye (OB) and Onnuri (ON) basins (Kim et al, 2022; Figure 1c). In the Cenozoic, the SKP was deformed by extension associated with back‐arc rifting and separation of the southwestern Japan Arc (Kim, Lee, Choi, et al, 2015; Kim, Lee, Park, et al, 2015).…”