Open AccessShear‐wave splitting variation over short spatial scales on continents
Author(s) -
Helffrich George,
Silver Paul,
Given Holly
Publication year - 1994
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1994.tb00142.x
Subject(s) - geology , lithosphere , seismology , shear wave splitting , tectonics , shear (geology) , plate tectonics , crust , shear zone , subduction , continental crust , intraplate earthquake , geophysics , mantle (geology) , paleontology
SUMMARY We have analysed broad‐band SKS, SKKS, PKS and S data from 12 stations of the IRIS/IDA network for shear‐wave splitting parameters, fast polarization direction ø and delay time δ t . These include several stations in the Former Soviet Union (FSU) (GAR, ARU, KIV, TLY, AAK, OBN), as well as SUR (Sutherland, South Africa), ESK (Eskdalemuir, UK), ALE (Alert, NWT, Canada), NNA (Naña, Peru), PFO (Piñon Flat, CA, USA), and ERM (Erimo, Japan). We compare observations from these stations with those from other nearby stations to gain insight into the mechanisms by which the anisotropy registered by split shear waves may arise. Intraplate comparisons exclude absolute plate motion as an orienting mechanism. Alternatively, the anisotropy may be linked to either fossil deformation within the continental lithosphere or to small‐scale convection. The close correspondence with geologic fabric supports the former interpretation. Commonly, the fast polarization direction is oriented parallel to the deformational axes of compressional tectonic regions. In regions of presently active tectonics, we also see fast polarization directions orthogonal to the maximum horizontal stress in the crust. Deformation localized in the margins of tectonic blocks may account for the spatial splitting variability, and can be facilitated by volatile fluxing of the continental lithosphere during the preceding subduction event.