Crustal-Scale Fault Systems in the Korean Peninsula Unraveled by Reflection Seismic Data

An approximately 40-km long high-resolution reflection seismic profile (P3) was acquired in the metropolitan area of Seoul in South Korea for the purpose of fault system imaging in a highly noisy and challenging urban environment. Two 12t seismic vibrators (mini-vibs) were used as the seismic source. Data were recorded using a dual element seismic spread; 20 m spaced 421 wireless seismic recorders connected to 10 Hz geophones and 20 micro-electro-mechanical-based landstreamer sensors (2 m sensor spacing) attached to one of the vibrators. The purpose of the dual spread employed was to delineate both near-surface and deep structures. The processing results show good quality and the processing work was complemented by different analysis to further constraints the geological interpretation. The survey results provide evidence for the 3D geometry of three fault systems, including Chugaryeong, Pocheon, and Wangsukcheon faults. A gently westerly dipping set of reflectivity underlying a dome-shaped package of reflectivity is interpreted as a fault, and could project to the known surface position of the Pocheon fault. The dome-shaped reflectivity is interpreted as folded and faulted dyke or sill systems. Downward continuation of the interpreted fault intersects the sub-vertical Chugaryeong fault in a zone where the current seismicity is observed, suggesting that these two major fault systems may have jointly evolved in the form of splay faults. Reflections from the Wangsukcheon fault are also present in the data and interpreted to dip approximately 60 degrees to the east, in an opposite direction to the two other faults. Plain Language Summary An approximately 40-km long high-resolution reflection seismic profile was acquired in the metropolitan area of Seoul in South Korea for the purpose of in-depth fault system imaging in a highly noisy and challenging urban environment. Two different types of receivers were used simultaneously to achieve good results from both shallow and deep structures. Processing results have good quality and are complemented with different analysis to further constraints the geological interpretation. The survey results provide evidence for the 3D geometry of three fault systems, including Chugaryeong, Pocheon, and Wangsukcheon faults. A gently westerly dipping structure underlying a dome-shaped structure is interpreted as a fault, and could project to the known surface position of the Pocheon fault. A dome-shaped reflectivity is interpreted as folded and faulted dyke or sill systems. Downward continuation of the interpreted fault intersects the sub-vertical Chugaryeong fault in a zone where the current seismicity is observed, suggesting that these two major fault systems may be connected and jointly evolved. Results from the Wangsukcheon fault are also present in the data and it is interpreted to approximately dip 60 degrees to the east, in an opposite direction to the two other faults.