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Constraints From Exhumed Rocks on the Seismic Signature of the Deep Subduction Interface
Author(s) -
TewksburyChristle C. M.,
Behr W. M.
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl093831
Subject(s) - subduction , geology , episodic tremor and slip , seismology , shear (geology) , shear zone , seismic anisotropy , anisotropy , ultramafic rock , deformation (meteorology) , petrology , geophysics , tectonics , geochemistry , mantle (geology) , oceanography , physics , quantum mechanics
Low Velocity Zones (LVZs) with anomalously high V p ‐V s 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 V p /V s of 2.0. Comparable thicknesses and velocities suggest that LVZs represent, at least in part, the subduction interface shear zone.