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Stress- and structure-controlled anisotropy in a region of complex faulting—Yuha Desert, California

June 1, 2015

We examine shear velocity anisotropy in the Yuha Desert, California using aftershocks of the 2010 M7.2 El Mayor-Cucapah earthquake. The Yuha Desert is underlain by a complex network of right- and left-lateral conjugate faults, some of which experienced triggered slip during the El Mayor-Cucapah earthquake. An automated method that implements multiple measurement windows and a range of bandpass filters is used to estimate the fast direction (ϕ) and delay time (δt) of the split shear waves. We find an average ϕ oriented approximately north–south suggesting it is primarily controlled by the regional maximum compressive stress direction. However, the spatial variability in ϕ reveals that the fault structures that underlie the Yuha Desert also influence the measured splitting parameters. We infer that the northeast- and northwest-oriented ϕ reflect shear fabric subparallel to the conjugate fault structures. We do not observe a simple correlation between δt and hypocentral distance. Instead, the observed spatial variation in δt suggests that near-source variation in anisotropic strength may be equal to or more important than effects local to the station. No temporal variation in splitting parameters is observed during the 70-day period following the main shock. In this region of complex faulting, we observe a spatially variable pattern of anisotropy that is both stress- and structure-controlled. This study suggests that shear fabric can form even along short, discontinuous fault strands with minimal offset.                   

Publication Year 2015
Title Stress- and structure-controlled anisotropy in a region of complex faulting—Yuha Desert, California
DOI 10.1093/gji/ggv191
Authors Elizabeth S. Cochran, Kayla A. Kroll
Publication Type Article
Publication Subtype Journal Article
Series Title Geophysical Journal International
Index ID 70155973
Record Source USGS Publications Warehouse
USGS Organization Earthquake Science Center