Geoscience Reference
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was also a notable increase in non-planktonic organisms at this level of the cores
suggesting a major influx of shallow water sediments to the deeper waters of
the lakeatthistime.
One of the potential problems associated with using lake sediments and tur-
bidites as evidence for past earthquakes is the difficulty in estimating the carbon
reservoir correction of those sediments, for radiocarbon determinations. Such
corrections are important because old carbon can be contained within the sed-
iments due to the carbon residence time in the catchment sediments before
they were deposited and submerged in the lake. The analysis is made easier if
there are calibration ages present, such as a known and accurately timed event.
When trees are submerged due to land subsidence during the earthquake, high-
precision dating of the outer rings of these trees can be used to calibrate the
radiocarbon dates from the lake sediments.
Archaeological evidence of prehistoric earthquakes
Archaeological evidence can help refine the temporal boundaries of past
seismic events. This evidence can be relatively easily dated either through abso-
lute geological dating techniques or through an understanding of the chrono-
logical changes experienced by various cultures, e.g. Chinese dynasties, Greek
and Roman architectural styles and occupation of various lands. The types of
evidence used to date prehistoric earthquakes often involve damage to build-
ings and infrastructure of a known age, and/or the cessation of occupation of
atown/city or region. In such situations the age of the buildings or features
provides a maximum age for the earthquake. A minimum age for the event
can be determined by the age of undamaged buildings or features at the same
site. These undamaged features are assumed to have been constructed after the
earthquake. The ages of the damaged, and presumably later constructed undam-
aged features, bracket the age of the earthquake. Of course bracketing an event
in this manner requires humans to have continued to occupy the site after the
earthquake.
Archaeological evidence can also assist palaeoseismological techniques where
occupation horizons in buried sedimentary sequences are cut across by sand
blows and/or microfaults. In such situations the palaeoseismological features
must post-date the archaeological evidence. The most commonly found artefacts
used for dating of historic cultural sequences, and occupation horizons, are
pottery shards and charcoal. Dateable objects can also include plant remains
from agricultural activities or those occurring naturally and associated with a
particular climate, possibly conducive to human occupation of a region for a
period of time. Objects and plant evidence can be matched with artefact types
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