Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
CHARACTERISTICS AND PALEOSEISMIC STUDY OF THE QUATERNARY
EUPCHEON FAULT IN SOUTHEAST KOREA
M. Lee (1), S.R. Han (1), T. Shim (2) and Y.S., Kim (1, *)
(1) Dept. of Environmental Geosciences, Pukyong National University, Busan 608‐737, KOREA.
(2) Safety Technology Division, Korea Institute of Nuclear Safety, Daejeon 305‐338, KOREA. * ysk7909@pknu.ac.kr
Abstract: The Eupcheon Fault is one of the Quaternary faults developed in southeastern part of Korean peninsula. The fault is located 1.8 km
away from the Weolsung nuclear power plant to the south. Based on the fault analysis developed in marine terrace deposits, the Eupcheon
Fault was developed as a syn‐depositional fault. At least four faulting events are recognized based on colluvial wedges and displacement‐
distance (d‐x) analysis. The Eupcheon Fault cuts the third level Quaternary marine terraces (40‐50 m), which is relatively higher compared with
other regions (25‐33m). An N‐S trending fault is discovered in the northern extent of the Eupcheon Fault, which composed of several fault
gouges indicating multiple deformations. The hanging wall block of the fault shows highly damaged fracture patterns indicating that the
hanging wall is weaker than footwall. Therefore, detailed analysis of fault characteristics and fault zones must be a very useful way to assure
the seismic hazard assessment of the site for nuclear power plants.
Key words: Eupcheon Fault, fault analysis, displacement‐distance, seismic hazard assessment
INTRODUCTION
Generally, the Korean peninsula has been considered as
tectonically safe region from earthquakes, because it is
located in stable margin of the Eurasian plate. However,
more than 36 Quaternary faults have recently been
reported from the southeastern part of Korea (Fig. 1; Kee
et al., 2007). These Quaternary faults are almost
distributed around the Yangsan and Ulsan faults, SE
Korea. Recently the Eupcheon Fault is reported (Kyung et
al., 1999; Chang, 2001; Park et al., 2006) close to the
Weolsung Nuclear Power Plant (WNPP), which is located
1.8 km away from the WNPP to the south. Seismic hazard
assessment associated with the Eupcheon Fault is very
important in terms of the safety concerns in nuclear
power plant industry. Therefore, we described the basic
geometry and characteristics and interpreted movement
seismic history of the fault. For this purpose, geometric
analysis and d‐x analysis are carried out from a trench
excavated across the Eupcheon Fault to understand its
movement history and kinematics (Kim et al., in review).
Furthermore, detailed fault zone analyses are carried out
in the northern extent of the fault to understand the
condition of site foundation.
LOCAL GEOLOGIC SETTING
The basement of the study area consists of Cretaceous
sediment rocks, which have been intruded by Cretaceous
and Tertiary igneous rocks, mainly granites and dykes of
various compositions. The intraplate deformation of
microplates initiated back‐arc rifting and the spreading of
the East Sea in the Oligocene to early Miocene (e.g.
Kimura & Tamaki, 1986; Yoon & Chough, 1995). Tertiary
basins along the eastern margin of the Gyeongsang Basin
are associated with the extension of the East Sea.
Collision of the Bonin Arc with central Honshu caused
back‐arc closing and crustal shortening in the Middle
Miocene (e.g. Kim and Park, 2006).
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Fig. 1: Distribution of Quaternary faults (yellow circle) in
southeast Korean Peninsula (WNP: Weolsung Nuclear Power
Plant, KNP: Kori Nuclear Power Plant; from Kee et al., 2007).
Thirty‐six, Quaternary fault close to study area have been
mapped in detail. Most of them show a right lateral
strike‐slip or reverse movement (Kyung et al., 1999;
Chang, 2001; Park et al., 2006) coincident with focal
mechanism solution from recent earthquakes (Kim et al.,
2006; Park et al., 2007). According to the focal mechanism
solution (Kim et al., 2006), both the subducting Pacific
plate and the collision of the Indian Plate with the
Eurasian continent result in a maximum principal stress