Geophysical Response of the Mission Creek Fault Near Desert Hot Springs, California

Geophysical surveys crossed the Mission Creek Fault, a branch of the San Andreas Fault system near Desert Hot Springs, California. The fault is situated in the alluvial Coachella Valley, and is a major barrier to groundwater flow. The fault trace is marked sporadically by oases and vegetation, and is associated with hot springs and hot water wells. Resistivity, VLF, VLFresistivity, and horizontal-loop electromagnetics (HLEM) have been employed to visualize the subsurface near the fault, and image the fault gouge. The main geophysical response is due to the water table which is deeper on the southwest side of the fault, according to observations in nearby wells. We believe that the geophysical response of the fault is distinct enough to allow its delineation in other locations where not exposed and/or mapped. The measurements were carried out as an undergraduate field trip and class project.