Physical modeling of microseismics and time reversal
Joe Wong, Hongliang Zhang, Kevin L. Bertram, Kristopher A. Innanen
We have conducted two physically-modeled experiments: a microseismic survey to acquire survey data for hypocenter location through an HTI layer, and a time reversal-time study demonstrating propagation reciprocity and wave focusing. Hypocentre location in 3D is normally done using raytracing to match observed event times. In our case, raytracing requires formulas giving accurate description of anisotropic velocities through HTI media. We suggest that the Byun equations are suitable for this purpose.
To completely replicate time-reversal experiments reported in the literature, we must drive the ultrasonic transducers used as seismic sources in physical modeling with time-reversed seismic traces. At present, we can drive source transducers only with impulse functions. Therefore, we have conducted our time-reversal experiment with impulses properly delayed to enforce the main point of time-reversal, which is that multiple sources can be activated in such a way so as to focus acoustic energy at a compact zone centred about a single point. The impulsive waveforms recorded in the physically-modeled experiment can be numerically convolved with a time-reversed received signal. This procedure yields a simulation of data that would have resulted if we had actually used such a waveform to drive the sources in acquisition.