Refraction of Fault-Zone Guided Seismic Waves

Finite-difference synthetic seismograms were computed for a surface source and a surface receiver array along and within a low-velocity fault damage zone. This survey geometry is analogous to a body-wave refraction survey along the fault trace. The synthetic data demonstrate that dispersive fault-zone guided waves are refracted by an increase in both fault-zone and crustal velocity with depth. Refraction of the guided waves allows the surface source and surface array to record waves that sample the deep fault zone. At each frequency, the observed group arrival times can be inverted for a 1D or 2D model of group velocity within the fault plane. The synthetic seismograms were successfully used to derive the fault-zone properties in the subsurface. Using multiple sources and receivers, this method can be used to derive 3D fault-zone structure to seismogenic depths, mapping variations both along strike and in depth.