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- Thursday, September 25, 2003
- Boundary-layer mantle flow under the Dead Sea transform fault inferred from seismic anisotropy
- Published at:Not Found
Lithospheric-scale transform faults play an important role in the
dynamics of global plate motion. Near-surface deformation fields
for such faults are relatively well documented by satellite geodesy,
strain measurements and earthquake source studies
, and
deeper crustal structure has been imaged by seismic profiling
.
Relatively little is known, however, about deformation taking
place in the subcrustal lithosphere—that is, the width and depth
of the region associated with the deformation, the transition
between deformed and undeformed lithosphere and the interaction
between lithospheric and asthenospheric mantle flow at
the plate boundary. Here we present evidence for a narrow,
approximately 20-km-wide, subcrustal anisotropic zone of
fault-parallel mineral alignment beneath the Dead Sea transform,
obtained from an inversion of shear-wave splitting
observations along a dense receiver profile. The geometry of
this zone and the contrast between distinct anisotropic domains
suggest subhorizontal mantle flow within a vertical boundary
layer that extends through the entire lithosphere and accommodates
the transform motion between the African and Arabian
plates within this relatively narrow zone.
At the southern end of the Dead Sea transform (DST), between
the Dead Sea and the Red Sea, the Wadi Arava fault is the main
active strike-slip fault
trending approximately N20E. Near the
Figure 1
, Map with topography and
the locations of seismic stations for which the shear-wave splitting analysis was
performed. The Arava fault (black line) strikes at approximately N20E. The bars indicate
measured SKS splitting parameters for the period range of 2–5 s (blue) and 5–7 s (red).
The orientation corresponds to the polarization direction of the fast shear wave (fast
polarization
, Measured shearwave
splitting parameters (circles) along the profile (delay times and fast polarization
directions) for the two period bands (2–5 and 5–7 s). The parameters are obtained by
application of an inverse splitting operator to minimize the energy of the transverse SKS
component
. A measure of error has been derived from the 95% confidence region as
determined by the
distribution. For reasons of representation a factor of 0.4 is applied
to the error scales used in this figure. The lines represent a smoothed version of the
measurements, calculated by averaging the results within a sliding window.
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