An-Najah National University

Radwan J. El-Kelani,

 

 
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  • Thursday, September 25, 2003
  • Boundary-layer mantle flow under the Dead Sea transform fault inferred from seismic anisotropy
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    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

     

    1,2

    , and

    deeper crustal structure has been imaged by seismic profiling

     

    3

    .

    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

     

    4–6

    trending approximately N20E. Near the

    Figure 1

     

    Study area and shear-wave splitting parameters. a

    , 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

     

    f) and the length is proportional to the delay time dt–1 s. b

    , 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

     

    17

    . A measure of error has been derived from the 95% confidence region as

    determined by the

     

    x 2

    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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PROFILE

Radwan J. El-Kelani
Associate Professor in Applied and Environmental Engineering Geophysics
 
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