Seismic hazard in regions of present day low seismic activity: uncertainties in the paleoseismic investigations along the Bree Fault Scarp (Roer Graben, Belgium)
K. Atakan et al., Seismic hazard in regions of present day low seismic activity: uncertainties in the paleoseismic investigations along the Bree Fault Scarp (Roer Graben, Belgium), SOIL DYN EA, 20(5-8), 2000, pp. 415-427
Earthquake hazard assessment in stable continental regions, such as norther
n Europe, has traditionally been evaluated on the basis of the instrumental
ly and historically recorded seismicity, which indicates relatively low haz
ard levels. Reliability of such estimates is a matter of debate as the long
-term potential of large earthquakes usually cannot be determined based on
short observational periods generally less than a few hundred years. A sign
ificant improvement to this lack of knowledge can be achieved by extending
the past observations into the geological time scale. Paleoseismic investig
ations can provide valuable information to bridge this gap, where the poten
tial for large earthquakes can be quantified both in magnitude and recurren
ce period, based on the observation of prehistoric earthquakes (paleoearthq
uakes) in the geological record (particularly in the last 20,000 years). Ho
wever, using these records in seismic hazard analysis requires systematic t
reatment of uncertainties. Usually uncertainties are inherent to the interp
retation of geological record, which leads, in the end, to the identificati
on of paleoearthquakes. Field observations used in the analysis may satisfy
several alternative interpretations. Such interpretations become useless w
hen alternative solutions exist but not documented in detail, and especiall
y when the relative reliability of the favored interpretation with respect
to the alternative interpretations is not known. The recently introduced me
thod using logic-tree formalism, which is based on qualitative description
of the uncertainties related to the paleoseismic data and especially in its
interpretation, is applied in the paleoseismic investigations performed on
the Bree Fault Scarp, along the Feldbiss Fault (Roer Graben, Belgium). The
cumulative uncertainties associated with the different stages of the study
are computed as the combination of the preferred alternative branches in t
he logic tree presentation. The final uncertainty and its relative importan
ce in seismic hazard analysis is expressed as the paleoseismic quality fact
or (PQF), which indicate 0.76. This value can directly be used in seismic h
azard analysis. (C) 2001 Elsevier Science Ltd. All rights reserved.