Seismic time reversal mirror: Field experiment

Time Reversal Mirror (TRM) is a physical process which refocuses recorded waves into their initial source location. We demonstrate how seismic P-wave is successfully focused back to its original location in a 3D field experiment. The method does not require a-priori knowledge of seismic velocities in the medium for re-focusing to occur. We further examine the observed focusing resolution of the back propagated wavefield by quantitative comparison to acoustic numerical modeling. As in any TRM process, the experiment includes two stages: in the first stage the seismic wave is generated by a sub-surface point source and recorded by a 3D surface array (the mirror). In the second stage, we activate a vibrator, based on a linear synchronous motor (LSM) to re-emit the time-reversed signals from the original receiver positions. As opposed to standard hydraulic-based seismic vibrators, the LSM-based vibrator enables generation of arbitrary seismic signals, efficiently acting as a reversal mirror. We record the re-emitted wavefield at sub-surface locations, near and at the original source location. Both real and modeled data focus the re-emitted data within the theoretical range of half the dominant wavelength, validating the TRM experimental results. Various applications of the TRM in seismic are considered.