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Constraints from exhumed rocks on the seismic signature of the deep subduction interface
  • Carolyn Morgan Tewksbury-Christle,
  • Whitney M. Behr
Carolyn Morgan Tewksbury-Christle
Department of Earth Sciences, ETH Zurich

Corresponding Author:carolyn.tewksbury-christle@erdw.ethz.ch

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Whitney M. Behr
Department of Earth Sciences, ETH Z├╝rich
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Abstract

Low Velocity Zones (LVZs) with anomalously high Vp-Vs ratios occur along the downdip extents of subduction megathrusts in most modern subduction zones and are collocated with complex seismic and transient deformation patterns. LVZs are attributed to high pore fluid pressures, but the spatial correlation between the LVZ and the subduction interface, as well as the rock types that define them, remain unclear. We characterize the seismic signature of a fossil subduction interface shear zone in northern California that is sourced from the same depth range as modern LVZs. Deformation was distributed across 3 km of dominantly metasedimentary rocks, with periodic strain localization to km-scale ultramafic lenses. We estimate seismic velocities accounting for mineral and fracture anisotropy, constrained by microstructural observations and field measurements, resulting in a Vp/Vs of 2.0. Comparable thicknesses and velocities suggest that LVZs represent, at least in part, the subduction interface shear zone.
28 Sep 2021Published in Geophysical Research Letters volume 48 issue 18. 10.1029/2021GL093831