Field measurements of azimuthal anisotropy: First 60 meters, San Francisco Bay area, CA, and estimation of the horizontal stresses’ ratio from Vs1/Vs2

Abstract

[Formula: see text], Q) of near‐surface strata. The azimuthal anisotropy revealed in these field experiments is the result of a combination of circumstances: unequal horizontal stresses (the data were collected near the center of the San Andreas and associated fault systems), fabric anisotropy introduced by the depositional agent, and stress‐aligned fluid‐filled microcracks, cracks, or pore spaces.