Heather Kennedy , Claudia Finger, Katrin Löer, Amy Gilligan

Rayleigh waves are prevalent in the ambient seismic noise wavefield and
are thus often exploited in passive seismic methods to characterise the near
subsurface. In fractured or faulted media, Rayleigh waves show azimuthal
anisotropy that could provide information on the fault properties. However,
the exact relationship between Rayleigh wave anisotropy and true anisotropic
structures is not well known. This study used a three-component (3C) beam-
forming toolbox to analyse numerical full waveform seismic wave propagation
from conceptual models of fractured media. We identify Rayleigh waves in
the synthetic data, compare observed Rayleigh wave anisotropy to structural
anisotropy, and assess the effect array design and source locations have on
Rayleigh wave analysis and observed anisotropy. Numerical analysis shows
that the smaller the velocity contrast between fault and surrounding rock,
the more complex the anisotropic response. We find that the slow directions
of Rayleigh wave propagation can be a better indicator of fault strike than
the fastest direction, when the velocity contrast between the two media are
small.