Paleoseismicity is defined as the study of the occurrence,
size, timing,
and frequency of prehistoric earthquakes. Paleoseismic data may be
gathered from
fault exposures, faulted landforms, fault scarps, stratigraphic
features, and
geomorphic features. The main goal of paleoseismology is the study of
large
earthquakes of the past on the basis of their geologic and geomorphic
expression to provide new and useful information for seismic hazard
evaluations. The recognition and dating of individual paleoearthquakes
and/or
of the cumulated deformation produced by repetead earthquakes on the
same fault
permit to characterize the seismic behaviour of the fault itself. In
fact,
using traditional geologic and geomorphologic metholodologies,
paleoseismological investigations provide the insights to estimate the
main
parameters indicating the behaviour of a seismogenic
(earthquake-producing)
fault. Results of trenching across the eastern Duzce Fault document
that
surface rupture has occurred repeteadly on the fault prior to the 1999
Duzce
earthquake, and that offset during previous earthquakes occurred at the
same
location and with similar amounts and type of slip as that of the 1999
earthquake. The most recent pre-1999 earthquake on the fault occurred
about 300
years ago. At least four and possibly five earthquakes (including 1999)
have
occurred in the past 2100 years. The earthquake recurrence interval
ranges from
300 to 800 years. Trench investigation across the surface rupture zone
associated with the Mudurnu Valley, western Turkey, earthquake of July
22,
1967, and revealed evidence for the last two faulting events including
the 1967
earthquake. On the basis of the radiocarbon dates of sediments in the
trench,
the occurrence of the penultimate event
is estimated most conservatively after 1480 A.D., but it is likely
believed
that the event occurred shortly after 1650 (±20) A.D. The
penultimate event is
likely to be correlated with the Anatolian earthquake of August 17,
1668, which
caused severe damage along the North Anatolian Fault System for about
600 km
from Bolu to Erzincan. At present, paleoseismological data exist only
for a
limited number of seismic regions of the world but these investigations
are
already started, or are going to be started soon, in several other
countries.
Steps of the paleoseismological research, describing the more common
techniques
that are largely suitable for several regions of the globe, may provide
good
results for recognizing the expression of paleoearthquakes and
quantifying the
fault parameters.