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Tectonic inheritance during plate boundary evolution in southern California constrained from seismic anisotropy
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  • Vera Schulte-Pelkum,
  • Thorsten Wolfgang Becker,
  • Whitney M. Behr,
  • Meghan Samantha Miller
Vera Schulte-Pelkum
CIRES/Geol. Sci., University of Colorado at Boulder

Corresponding Author:[email protected]

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Thorsten Wolfgang Becker
University of Texas at Austin
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Whitney M. Behr
Department of Earth Sciences, ETH Zürich
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Meghan Samantha Miller
Australian National University
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Abstract

The style of convective force transmission to plates and strain-localization within and underneath plate boundaries remain debated. To address some of the related issues, we analyze a range of deformation indicators in southern California from the surface to the asthenosphere. Present-day surface strain rates can be inferred from geodesy. At seismogenic crustal depths, stress can be inferred from focal mechanisms and splitting of shear waves from local earthquakes via crack-dependent seismic velocities. At larger depths, constraints on rock fabrics are obtained from receiver function anisotropy, Pn and P tomography, surface wave tomography, and splitting of SKS and other teleseismic core phases. We construct a synthesis of deformation-related observations focusing on quantitative comparisons of deformation style. We find consistency with roughly N-S compression and E-W extension near the surface and in the asthenospheric mantle. However, all lithospheric anisotropy indicators show deviations from this pattern. Pn fast axes and dipping foliations from receiver functions are fault-parallel with no localization to fault traces and match post-Farallon block rotations in the Western Transverse Ranges. Local shear wave splitting inferences deviate from the stress orientations inferred from focal mechanisms in significant portions of the area. We interpret these observations as an indication that lithospheric fabric, developed during Farallon subduction and subsequent extension, has not been completely reset by present-day transform motion and may influence the current deformation behavior. This provides a new perspective on the timescales of deformation memory and lithosphere-asthenosphere interactions.
Nov 2021Published in Geochemistry, Geophysics, Geosystems volume 22 issue 11. 10.1029/2021GC010099