7
Conclusions
We have acquired an approximately 40-km long reflection seismic profile
intersecting three major fault systems (Chugaryeong, Pocheon and
Wangsukcheon faults) in the broader metropolitan area of Seoul in South
Korea. The data are consistent with the Chugaryeong fault being a
sub-vertical structure below the location where it is geologically
mapped. From a seismic viewpoint, surface-waves show strong back
scattering from it and it shows no coherent reflectivity. A 30-degree NW
dipping zone of reflectivity underlying a dome-shaped reflective package
is imaged in the central part of the migrated stacked section and it is
interpreted as a fault. A dyke or sill system intersected by the
propagating fault has resulted in the fault-bend fold structures
(dome-shaped reflectivity). This fault if projected downwards would
intersect a series of seismic events at the intersection with the
Chugaryeong fault. This further suggests, and confirms a recent
speculation, a relation between the two faults concerning the
intersection and the seismicity, with the implication that both faults
may be active and form splays. If this fault is projected to the surface
it will intersect Pocheon fault surface expression and related strong
surface wave back scattering, unfortunately there is no imaging of the
near surface geometry of Pocheon fault to confirm or reject this
possibility. The Wangsukcheon fault, on the other hand, is found to have
a N20E/60E geometry, implying an opposite dip angle from the other two
faults. There is no related seismicity associated with the Wangsukcheon
fault in the area, which may justify why it has completely different
geometry with respect to the two other faults.
Data availability . Original data underlying the material
presented are available by contacting the corresponding author. However,
as the dataset is the subject of other PhD studies, there is a period of
3years embargo on their availability.
Acknowledgments. We thank the contributions of many students and
post-docs from Yonsei University and Uppsala University, Geopartner and
C&H Company. Chiara Colombero and Politecnico di Torino provide access
to the surface waves back scattering energy computation code.
Author contributions . TKH initiated the project, organized the
acquisition and was involved in the discussions of the results and their
interpretations. SZ is responsible for the data preparation, for most of
the data processing, for the traveltime tomography, for the crossdip
analysis, for the interpretations and for the writing of the article. AM
led the data acquisition, processed most of the landstreamer data,
helped with the overall processing and especially with the writing of
the article and the interpretational aspects and discussion. CJ worked
in the first part of the data processing highlighting the Wangsukcheon
fault reflection and modeling its reflection traveltime. JL helped on
the acquisition setting and organization and prepared the basis for the
maps. MP worked on the surface-wave back scatterings analysis. BB
contributed in the data acquisition and planning. TKH, BB, CJ, JL, MP,
SP, DC, BK and JeL contributed to the final preparation of the paper.
Financial support . This work was supported by the Korean
Meteorological Administration (KMA) Research and Development Program
under grant KMI2022-00710, and partly by the Basic Science Research
Program of National Research Foundation of Korea
(NRF-2017R1A6A1A07015374).