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Crustal anisotropy in southern California from local earthquake data
Author(s) -
Paulssen Hanneke
Publication year - 2004
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 - 10.1029/2003gl018654
Subject(s) - geology , shear wave splitting , anisotropy , azimuth , seismology , isotropy , crust , shear (geology) , transverse plane , seismic anisotropy , perpendicular , shear waves , geophysics , geometry , physics , petrology , optics , mantle (geology) , mathematics , structural engineering , engineering
Shear wave splitting measurements were made for local earthquakes in southern California at incidence angles larger than the critical incidence angle. For the region of San Bernardino Mountains, the fast polarization directions vary strongly, but are consistently fast for directions roughly perpendicular to the ray paths. This observation is most readily explained by transverse isotropy with a vertical symmetry axis, and is probably associated with horizontally foliated gneisses or schists in the upper crust. Other measurements show a predominance of north‐south fast directions, while some data have fast directions that are parallel to the San Andreas fault. These observations are related to azimuthal anisotropy as found in other local shear wave splitting and SKS splitting studies. The data show that, apart from the free surface effect, shear wave splitting measurements for shear waves at shallow incidence angles can have an imprint of transverse isotropy as well as azimuthal anisotropy.