Laterally Varying Crustal and Quaternary Fault-Zone Structures in the Seoul Metropolitan Area, South Korea, from a Joint Inversion Analysis Based on Dense Seismic Arrays

Abstract

The crustal structure and Quaternary fault zone in the Seoul metropolitan area are investigated using a joint inversion that combines the receiver functions with surface wave dispersion based on seismic data from densely deployed seismic arrays. The uncertainty in inverted models is examined through a set of synthetic experiments. Synthetic tests and comparisons with other methods verify the observed crustal features. The Moho depths range between 28.7 and 32.8 km with relatively shallow depths in the central Seoul metropolitan area. The VP/VS ratio varies between 1.67 and 1.85. A Conrad discontinuity with a weak velocity increase is present at a depth of ∼20 km. Low-velocity anomalies appear at depths of ∼3 km and 6–11 km along the Chugaryeong fault zone and fault junction area. Apparent shear wave velocity contrasts appear across the fault zone where earthquakes are clustered. A high-velocity block in the western Seoul metropolitan area lies along the fault zone that runs across western Seoul. The shear wave velocity models and seismicity suggest that the fault zone may extend to a depth of 11 km at least.

Role of Backbone Fault System on Earthquake Spawning and Geohazards in the Seoul Metropolitan Area

“…Major faults are presented (thin solid lines). Lee et al, 2022). The seismic tomography and seismic reflection studies suggest subvertical structures in Chugaryeong (Dongducheon) fault (Kil et al, 2021;Malehmir et al, 2022;Zappalá et al, 2022).…”

“…The focal mechanism solutions agree with the fault traces (Hong et al., 2021) (Figure 1). Recent studies reveal large seismic‐velocity contrasts across the faults at depth (Kil et al., 2021; Lee et al., 2022). The seismic tomography and seismic reflection studies suggest subvertical structures in Chugaryeong (Dongducheon) fault (Kil et al., 2021; Malehmir et al., 2022; Zappalá et al., 2022).…”

“…On the other hand, the central‐to‐southern Seoul metropolitan area presents relatively low seismicity (Figure 1). Also, clustered earthquakes appear to occur around major fault systems where medium contrasts and interfaces are located (Hong et al., 2021; Kil et al., 2021; Lee et al., 2022; Malehmir et al., 2022).…”

Displacement of Dongducheon and Wangsukcheon Fault Observed by Gravity Field Interpretation

“…서 언 한반도 중부의 수도권 지역은 남-북 방향 및 북북동-남 남서 방향으로 발달하는 추가령 단층대(Fig. 1A의 CFS) 가 분포한다 (Choi et al, 2012;Chung et al, 2014;Choi et al, 2021;Kil et al, 2021;Lee et al, 2022). 추가령 단 층대는 동해안 원산에서 추가령에 이르는 협곡을 지나며 한반도 중부 지역인 평강, 철원, 연천 및 서울의 삼각산 과 북한산을 통과하여 남쪽으로 충청남도 서해안까지 이 어지는 대규모 구조대로 최소 4개 이상의 단층으로 구분된 다(Fig.…”

Analysis of the Causes of Clustered Scismicity Registered in Yeoncheon, the Middle Part of the Korean Peninsula through Gravity Field Interpretation and Modeling

“…1C 의 빨간색 세모)의 지진이 관측되었고 최대 규모와 평균 규모는 M2.9와 M1.4였다. 반면, 경주지진 이후 2018년 부터 2021년까지 4년간 303 회로 지진의 발생 빈도가 증 가하였고 (Kil et al, 2021;Lee et al, 2022), 지진규모가 1.0 미만의 군발성 지진을 특징으로 한다(연세대학교 자 료 제공). 더욱이 이 지역에서 최근에 발생한 미소지진의 대부분이 동두천 단층과 인접한 지역에서 집중적으로 발 생하였다는 것이 우려되는 점이다(Fig.…”