The surveys were completed on a sandy beach in Monterey Bay, California. The same geometry and acquisition parameters were used for both surveys to minimize differences unrelated to fluid changes. The source was a 0.25 kg hammer, and geophone spacing was 20 cm. These acquisition parameters coupled with the homogeneous nature of the sand allowed significant energy above 800 Hz to be recorded in the shot records. Figure 1 shows a typical shot record before and after high-pass filtering to remove the ground-roll. Despite the narrow bandwidth of the signal, at least two distinct hyperbolic events are visible in the filtered gather.
Since the honey was added to the top 2 m of the subsurface, we were not able to image it directly. Instead we looked for changes in the response of the water-table below. Theory predicted that the primary effect of the honey would be one of attenuation.
The surveys had been designed to see if it was possible to detect 20 liters of honey that had been mixed with 200 liters of sand at one location along the survey line, giving approximately 25% pore-space saturation.
In this paper, we are concerned only with the problem of cross-equalizing the datasets. We will cover the motivation and rock physics fully in later papers. However, in summary, the experiment follows up on earlier shallow seismic experiments described in Bachrach and Nur (1997) and Bachrach et al. (1997), and theoretical work concerning partial saturations Bachrach and Dvorkin (1997).