A tale of two realities; reconciling physical and numerical modeling via 'bootstrap' processing

David C. Henley

Seismic physical modeling is the process of conducting seismic surveys on laboratory scale models of earth structures, using ultrasonic transducers, to simulate the expected seismic response to similar structures in the earth. From modeling results, we improve our understanding of the generation and propagation of various elastic and acoustic wave modes in the real earth. Because of the similarity to seismic field surveying, physical model results can be considered a form of 'ground truth' for geology accurately represented by the model. Numerical modeling, on the other hand, creates a simulated seismic response to a digital representation of a physical earth structure. It is useful not only for evaluating how well a digital model represents the earth, but also for verifying the modeling process itself. Numerical modeling plays a significant role in Full Waveform Inversion, since a modeling algorithm is used to compute a seismic response to the most current earth model to compare with the most current processed input data, in order to update the model. Using a scale model constructed and surveyed in the CREWES physical modeling lab, we have the unique opportunity to compare images obtained from the physical model survey data with images produced by the data from numerical modeling of a digital representation of the laboratory scale model. We initially have only a schematic of the laboratory physical model, however, so we first use the schematic, along with an image from the physical survey itself, to create the digital model for input to the numerical modeling algorithm. The physical model data are then re-imaged using this estimated digital model velocity field, and the model itself updated--a 'bootstrap' approach. We then use a finite difference acoustic numerical modeling algorithm to create a CMP survey of the digital model, emulating the acquisition geometry of the actual survey. The numerical data are processed identically to the physical model data. We compare the physical and numerical model images.