Abstract
Fault zones are the locations where motion of tectonic plates, often
associated with earthquakes, is accommodated. Despite a rapid increase
in the understanding of faults in the last decades, our knowledge
of their geometry, petrophysical properties, and controlling processes
remains incomplete. The central questions addressed here in our study
of the Dead Sea Transform (DST) in the Middle East are as follows:
(1) What are the structure and kinematics of a large fault zone?
(2) What controls its structure and kinematics? (3) How does the
DST compare to other plate boundary fault zones? The DST has accommodated
a total of 105 km of left-lateral transform motion between the African
and Arabian plates since early Miocene (\~20 Ma). The DST segment
between the Dead Sea and the Red Sea, called the Arava/Araba Fault
(AF), is studied here using a multidisciplinary and multiscale approach
from the micrometer to the plate tectonic scale. We observe that
under the DST a narrow, subvertical zone cuts through crust and lithosphere.
First, from west to east the crustal thickness increases smoothly
from 26 to 39 km, and a subhorizontal lower crustal reflector is
detected east of the AF. Second, several faults exist in the upper
crust in a 40 km wide zone centered on the AF, but none have kilometer-size
zones of decreased seismic velocities or zones of high electrical
conductivities in the upper crust expected for large damage zones.
Third, the AF is the main branch of the DST system, even though it
has accommodated only a part (up to 60 km) of the overall 105 km
of sinistral plate motion. Fourth, the AF acts as a barrier to fluids
to a depth of 4 km, and the lithology changes abruptly across it.
Fifth, in the top few hundred meters of the AF a locally transpressional
regime is observed in a 100-300 m wide zone of deformed and displaced
material, bordered by subparallel faults forming a positive flower
structure. Other segments of the AF have a transtensional character
with small pull-aparts along them. The damage zones of the individual
faults are only 5-20 m wide at this depth range. Sixth, two areas
on the AF show mesoscale to microscale faulting and veining in limestone
sequences with faulting depths between 2 and 5 km. Seventh, fluids
in the AF are carried downward into the fault zone. Only a minor
fraction of fluids is derived from ascending hydrothermal fluids.
However, we found that on the kilometer scale the AF does not act
as an important fluid conduit. Most of these findings are corroborated
using thermomechanical modeling where shear deformation in the upper
crust is localized in one or two major faults; at larger depth, shear
deformation occurs in a 20-40 km wide zone with a mechanically weak
decoupling zone extending subvertically through the entire lithosphere.
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