Abstract
The Elat fault system in the southern Arava Valley (Dead Sea rift,
Israel) is a complex fault zone, characterized by marginal normal
faults and central sinistral strike- slip faults. Paleoseismic evidence
shows that the Elat fault system has generated at least 15 earthquakes
of magnitudes (M) larger than 6 during the late Pleistocene and the
Holocene. At least two branches of the fault zone were tectonically
active simultaneously, indicating that the seismic response over
a period of 80 k.y. was time and space dependent. Late Pleistocene
earthquakes displaced the surface by 1-1.5 m; their magnitudes were
between M 6.7 and M 7, and their average recurrence interval was
2.8 +- 0.7 k.y. Movements along the fault system in the Holocene
had a higher frequency and a recurrence interval of 1.2 +- 0.3 k.y.,
but resulted in smaller displacement amounts (0.2-1.3 m) and smaller
earthquake magnitudes (M 5.9-M 6.7). Historical records document
the last seismic event along the Elat fault zone at \~1000 yr ago.
The decrease in tectonic activity with time is inferred from the
concentration of offset along the fault segments in the central part
of the Elat fault zone and the decreased seismicity in the eastern
and western margins. The magnitude range determined for the central
zone (M 6.1-M 6.7) was likely not high enough to activate the marginal
faults. The average slip rate on the normal faults is 0.2 mm/yr.
However, the slip rate has changed through time on different fault
segments in the active wide shear zone and between clusters of events
related to the same segment. The event-specific slip rates, therefore,
have varied from 0.1 to 0.3 mm/ yr. The decrease in earthquake magnitudes
with time, combined with the observations that the last large event
occurred in A.D. 1068 and that no microseismicity has been detected
during the past 15 yr, might signal locking of the Elat fault zone.
This effect, if true, may result from episodic global reorganization
of the system's mode of strain- energy release, reflected in the
configurational entropy of stress states on the fault. These results
have significant implications for seismic hazard assessment in the
southern Arava Valley, southern Israel, and underscore the possibility
that the Elat fault may be a site of major earthquakes in the near
future.
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