Mapping stress and structurally controlled crustal shear velocity anisotropy in California

We present shear velocity anisotropy data from crustal earthquakes in California and demonstrate that it is often possible to discriminate structural anisotropy (polarization of the shear waves along the fabric of major active faults) from stress-induced anisotropy (polarization parallel to the maxi...

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Bibliographic Details
Published in:Geology (Boulder) 2006-10, Vol.34 (10), p.825-828
Main Authors: Boness, Naomi L, Zoback, Mark D
Format: Article
Language:English
Subjects:
active faults
Anisotropy
body waves
California
compression
crust
discriminant analysis
Earthquakes
elastic properties
elastic waves
faults
mapping
microearthquakes
polarization
S-waves
San Andreas Fault
seismic waves
seismographs
Seismology
shear
Shear stress
statistical analysis
stress
structural controls
three-component seismographs
United States
velocity structure
wave splitting
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Description
Summary:We present shear velocity anisotropy data from crustal earthquakes in California and demonstrate that it is often possible to discriminate structural anisotropy (polarization of the shear waves along the fabric of major active faults) from stress-induced anisotropy (polarization parallel to the maximum horizontal compressive stress). Stress directions from seismic stations located near (but not on) the San Andreas fault indicate that the maximum horizontal compressive stress is at a high angle to the strike of the fault. In contrast, seismic stations located directly on one of the major faults indicate that shear deformation has significantly altered the elastic properties of the crust, inducing shear-wave polarizations parallel to the fault plane.
ISSN:0091-7613
1943-2682
DOI:10.1130/G22309.1