Monitoring of Shallow Subsurface Anomalies With Seismic Waves

Human activity, such as extraction/injection of fluids or heat producing operations can cause significant changes in shallow subsurface. Monitoring of those changes is necessary for evaluation of the overall environmental impact and prevention of the unwanted scenarios. The existing seismic methods utilize surface waves for evaluating the elastic properties of the ground are based on 1D model and not capable to provide a suitable lateral resolution for imaging of contrast anomalies, which require a high resolution imaging. Contrast anomalies generate not just surface waves but also all kinds of scattered waves, which should be accounted for in the inversion process. A significant advancement in an imaging technology can be done using the full waveform inversion in the Fourier domain. For investigation of a sensitivity and resolution of the full waveform inversion we performed 3D modeling of elastic wave propagation in the media with a few vertical anomalies at different depths. The source of seismic signal is on the earth surface. The numerical simulation uses the three dimensional staggered-grid finite-difference method (Petrov and Newman, 2010). We consider scattering fields for a few configurations of anomalies and compute the response at different frequencies. Amplitude anomalies show much higher relative response compare to phase anomalies. The results suggest that the full waveform inversion in the Fourier domain should provide higher resolution and sensitivity than the existing 1D approaches. References. Petrov, P.V., G. A. Newman (2010), Using 3D Simulation of Elastic Wave Propagation in Laplace Domain for Electromagnetic-Seismic Inverse Modeling, Abstract T21A-2140 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.