Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

trending ENE/WSW in the Korean peninsula and
ESE/WNW in the east on the East Sea (Choi et al., 2008).
The Quaternary terrace deposits in the southeastern part
of the Korean Peninsula were developed parallel to the
coastline at five different elevations. The Eupcheon Fault
is developed in the third marine terrace about 30–50 m
above sea level. The marine terrace of the study area is
relatively higher than other regions indicating local
tectonic uplift. The average long‐term uplift rates are 0.31
(~0.3)m/ka in the study area, but other regions uplift
rates are 0.18 (~0.2) m/ka (Choi et al., 2008).
Fig. 2: Photomosaic and sketch logs of the northern lower trench
walls(a), displacement–distance (d–x) data for the northern (b).
Note that the trends show several step‐like features that indicate
cumulated displacement. The displacements accommodated by
drag folding are generally constant along the fault. However, the
displacements slightly increase in inverse proportion to the total
displacement, which may indicate that some of the displacement
associated with faulting is accommodated by folding at fault tips.
The displacement accommodated by drag folding is not included
to the amount of the total displacement (from Kim et al., in rev.)
GENERAL CHARACTERISTICS OF THE EUPCHEON FAULT
The Eupcheon Fault, one of the identified Quaternary
faults, was discovered during the construction of a
primary school in an area close to a nuclear power plant.
The Eupcheon Fault consists of one main reverse fault
(N20°E/40°SE) with approximately 6‐7m displacement,
and synthetic and antithetic faults. It also includes
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
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mesoscale structures such as hangingwall anticlines, drag
folds, back thrusts, pop‐up structures, flat‐ramp
geometries, fault‐related folds, and duplexes in
unconsolidated sediments (Kim et al., 2004). The
orientation of the new trench (Fig. 2) was about 140°,
almost perpendicular to the strike of the fault, and the
trench was about 25 m in length, 3‐5 m in width, and 8‐11
m in depth depending on the location within the trench
(Kim et al., in review; Fig. 2a).
The trench shows an upper section in the northern wall
that included three sedimentary wedges that correspond
to periods of surface faulting, and two lower sections that
recorded thrust events cutting the marine terraces. Kim
et al.(in review) measured the displacements across the
fault based on the established sedimentary sequences.
Some layers in the footwall are thinner than hanging wall,
which probably indicates the development of topographic
relief between hanging wall and footwall since
sedimentation and syn‐depositional faulting. Moreover,
d‐x profiles reveal consistent step‐like patterns indicative
of repeated faulting (Fig. 2b). Therefore, the total
cumulative displacement along the fault is about 6 m, and
four or five faulting events are recognized based on the
existence of colluvial wedges and the d‐x profiles.
Furthermore, these indicate that the amount of slip in
each event might be in the range of 0.7 to 1.8 m (Kim et
al., in review). Kim et al.(in review) suggests that this
maximum slip corresponds to earthquake magnitudes in
the range of Mw 6.3 to 7.0 based on the relationship
between maximum slip and moment magnitude
suggested by Wells and Coppersmith (1994).
AGE CONSTRAIN OF THE FAULT ACTIVITY AND THE
MARINE TERRACE DEPOSITS
Marine terraces are developed extensively along the
southeastern coast of the Korean peninsula. Marine
terraces are valuable materials for discerning late
Quaternary vertical displacement and deformation based
on optically stimulated luminescence (OSL) dating
method. The Eupcheon Fault cuts the unconsolidated
third level Quaternary marine terrace. Many studies
suggest the age of fault activity of the Eupcheon Fault,
using ESR and OSR age dating methods (e.g. Lee et al.,
2007, Choi et al., 2008, Choi et al., 2009). The reported
OSL age from this trench site in the third marine terrace is
in the range of 110‐120ka (Choi et al., 2003).
Based on the ESR dating result, the fault has been
reactivated at least five times such as 2000, 1300, 900‐
1100, 700‐800, and 500‐600ka ago. However, ESR dating
ages are older than the terrace ages, suggesting that they
do not represent the youngest faulting event. These data
suggest that the Eupcheon Fault can be classified as a
potentially active fault.
GEOMETRIC FAULT PATTERNS IN THE NORTHERN
EXTENT OF THE EUPCHEON FAULT
Recently, a east dipping, N‐S trending fault was
discovered during developed in the construction of new
Weolsung nuclear power plant construction site in the
northern extent of the Eupchon Fault.