Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
Fig. 3: The photographs of outcrops along the northern extent of the Eupcheon Fault in new Weolsung nuclear power plant(a, b). photo mosaic
and sketch map, and detailed photographs and sketches showing movement senses(c, d).
This location is the northern extent of the Euchon Fault.
The fault deformed the Cretaceous sedimentary rocks
developed in the construction site. of the Gyeongsang
supergroup. Well‐exposed vertical and horizontal sections
are analyzed so as to understand 3‐dimensional fault
geometry and fault evolution. A well exposed 1 km long
and up to 2m thick reactivated fault zone is studied
developed (Fig. 3). The main N‐S striking fault zone shows
various fault gouge bands and S‐C fabrics, which that
indicate discrete stages of normal and reverse fault
movements during several stages of deformation. The
fault gouges within the fault zone occur as splits or merge
into another fault zone rather than crosscut each other.
These may indicators suggest indicate that the major fault
has been evolved into in this study area ia mature fault
system.
FAULT SLIP ANALYSIS AND REACTIVATION
To understand the transport direction of the fault, we
analyzed the relative timing of kinematic indicators, such
as cleavages, lineations, and slickensides (Fig. 4a, b). The
results show consistent slip pattern (Fig. 4c). The slip data
indicates that the fault zone experienced repeated
movements including normal movement under SE
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extension and reverse movement under NNW
compression (Fig. 4d)
HAZARD ASSESSMENT AROUND THE EUPCHEON FAULT
Generally, earthquakes occur along preexisting active
faults (e.g. Ota, 1999; Chen et al., 2002; Ota et al., 2004;
Ota et al., 2005). This suggests that detailed mapping of
active faults is a key for understanding future surface
faulting. One of the important characteristics of
earthquake hazard is that no serious damage occurs on
the footwall although buildings are located very close to a
fault (Ota et al., 2005).
Hanging wall block in the study area also represents a
wide range of damages such as wide fracture zone, large
volume of distributed deformation, and alteration by
groundwater (Fig. 3a). Therefore, the fault geometries
and kinematics are important factors to evaluate
conditions of important sites. Furthermore, fault damage
zones (Kim et al., 2004) around faults are very important
indications for the seismic hazard assessment due to
secondary fractures and aftershocks (Kim and Sanderson,
2008).