Using Analytic Signal Analysis On Aeromagnetic Data To Constrain AMT Inversions, San Pedro River Basin, Sonora, Mexico
J.C. Wynn, US Geological Survey, Vancouver, Washington;
Floyd Gray, US Geological Survey, Tucson, Arizona;
T.E. Nordstrom, Dexin Liu, E.V. Reed, Zonge Engineering, Tucson, Arizona;
F.A. Villaseñor, SEMARNAT, Cananea, Mexico;
Gerry Connard, NGA Inc., Corvallis, Oregon
Paper — [pdf] AMT_Inversion_with_AeroMAG
On the American side of the San Pedro Valley basin, time-domain airborne geophysical methods were used to map the relatively conductive groundwater typical of an arid region to depths of 150 to 400 meters in the absence of human cultural interference. To better understand the hydrology of the basin as a whole, geophysical surveying has been extended southward into the Sonoran San Pedro Valley of northern Mexico.
We then conducted a scalar audio-magnetoelluric (AMT) survey over four different lines in the Sonoran San Pedro basin, and processed these data using a smooth-model inversion to conductivity-vs-depth profiles. As we view the conductivity inversion results, we are in fact visualizing the highly conductive water typical of an arid climate; in effect, we broadly image the saturated sediments. We then used an analytic signal depth-to-source algorithm on magnetic data along the same profiles to constrain the AMT inversion.
The result is a unique set of geophysical profiles that clearly show basement structure beneath the Sonoran San Pedro basin to depths of up to 800 meters. These constrained profiles help resolve basement controls on groundwater flow in northern Mexico leading to the US frontier.