Earthquakes - Extreme Events: A Physical Reconstruction and Risk Assessment - page 166

and cultivation patterns that have been dated on other similar sites. In many
regions in the United States, changes in artefact styles and types, and plant
cultivation, have been mapped for the last 12 000 years (Lafferty, 1996).
Greek, Hebrew, Assyrian, Roman, Byzantine and Islamic cultures repeatedly
reported the occurrence of large earthquakes throughout the Middle East over
thepast several thousands of years. Arab chroniclers described with details main
shocks, aftershocks, surface breaks and related damage distribution in the Mid-
dle East as early as the 7th and 8th Centuries. The same Arabic documents also
show that earthquakes have occurred less frequently over the last 830 years,
or since medieval times, along a section of the Dead Sea Fault known as the
70 km long Missyaf segment. Because of this inactivity, the northern section of
theDead Sea Fault in Lebanon and Syria is considered to be an inactive seis-
mogenic structure compared to other worldwide major strike-slip faults. Such
assumptions, however, can lead to an underestimation of the risk associated
with earthquakes in such locations, particularly if similar seismic gaps have
been common throughout the late Quaternary (Meghraoui et al ., 2003).
Meghraoui et al .(2003)undertook both an archaeoseismic and palaeoseismic
investigation of a site along the Missyaf segment of the fault in Syria. The archae-
ological evidence included a disrupted Roman aqueduct which spans the Dead
Sea Fault. The fault has experienced several episodes of left-lateral displacement
totalling 13.6 m during major earthquakes and this has resulted in severing and
relative displacement of each side of the aqueduct (Fig. 6.4). The age of the aque-
duct was bracketed to between AD 30 and 70 corresponding to the early Roman
period in the Middle East (post 64 BC). The geological evidence for large past
earthquakes resulting from movements of the Dead Sea Fault at the site include
faulted young alluvial, colluvial and lacustrine deposits, deflected streams with
consistent left-lateral displacements of tens to hundreds of metres, and evidence
of large shutter ridges and small pull-apart basins along the strike.
Palaeoseismic analysis involved trenching sediments at the site. The sedi-
ments contain pottery shards and detrital fragments of charcoal that were
radiocarbon dated. A 5 m deep section exposed seven separate units of alluvial
sediments. A 2 m wide shear zone with intense deformational structures and
numerous fault strands occurs in the sediments. This shear zone formed dur-
ing a number of large palaeoearthquakes. Sediments comprising the uppermost
unit (unit a in Fig. 6.5)are not sheared or faulted but rather cap these features.
This unit therefore has been deposited after the most recent earthquake and
provides a minimum age of AD 990--1210 for this event. The next stratigraphi-
cally lower unit (unit b Fig. 6.5)truncates two faults that have occurred after
deposition of the fourth highest stratigraphic unit (unit d Fig. 6.5) which was
radiocarbon dated at AD 680--890. This unit itself caps another sedimentary unit