The San Andreas Fault In Southern California Has a “Propeller” Shape—Implications for Tectonics and Seismic Hazard
Where traced through the crust in deep seismic studies or projected through the crust from upper-crustal studies, the SAF intersects the Moho on the immediate northeast side of the well documented upper-mantle high-velocity body of the Transverse Ranges, imaged from P-wave teleseismic tomography. It appears to continue to more than 150-km depth in the mantle along the northeast and north side of this body. In most places, the dip of the north side of this body is somewhat steeper than the dip of the SAF in the crust. We interpret this geometry to indicate a component of downwelling of PAC lithosphere along the plate boundary. Anisotropy may play a role in the visibility of the high-velocity body to teleseismic P-wave imaging owing to reorientation of the fast direction of olivine in the downwelling.
The dip of the SAF is important for estimating shaking potential for scenario major earthquakes and for calculating geodetic deformation.