Assessing Bulk Gravity Datasets in MATLAB for Preliminary Modeling of Basin Thickness; Case Study of Bridgeport Basin, Bridgeport, CA

Abstract:

Understanding the potential availability of water resources in Eastern California aquifers is of critical importance to making water management policy decisions and determining best-use practices for California, as well as for downstream use in Nevada. Hydrologic well log data can provide valuable information on aquifer capacity, but is often proprietarily inaccessible or economically unfeasible to obtain in sufficient quantity. In the case of basin-fill aquifers, it is possible to make estimates of aquifer geometry and volume using geophysical gravity surveys, constrained by additional geophysical and geological observations. In constructing a depth model for the Bridgeport, CA basin, we assess several hundreds of gravity observations. We regard these datasets as “bulk,” as the data are compiled from multiple sources. Inconsistencies among datasets can result in “static offsets,” or bull’s-eye contours, within the gradient. Amending suspect offsets requires the attention of the modeler; however, picking these offsets by hand can be a time-consuming process. We develop a MATLAB script for interpolating the Bouguer anomaly about the basin using sparse observation points, and locating the position of any offsets with a user-defined sensitivity. The script is also capable of plotting gravity profiles between any two endpoints within the map extent. The resulting anomaly map provides an efficient means of locating static offsets in the data, while also providing a fast visual representation of a bulk dataset. This process will help to illuminate new priority field sites for observations within the basin. Additionally, iteration of the preliminary model on newly incorporated data will show the effect of observation density on controlling static offsets.