Key points
• Reflection seismic imaging of fault systems in Seoul metropolitan
area.
• Suggested dependency of the regional seismicity from Chugaryeong fault
system.
• Deep geometry reconstruction of three regional fault systems.
Abstract.
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 (MEMS-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
domed-shaped package of reflectivity is interpreted as a fault, and
could project to the known surface position of the Pocheon fault. The
domed-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.