GEOPHYSICS AND PALEOSEISMOLOGY: THE SIGNATURE OF ACTIVE FAULTS IN THE GREAT BASIN

We show examples of locating and estimating the relative ages of suspected fault strands using three simple and inexpensive geophysical methods. In the east Gardnerville basin, Nevada, we used shallow seismic reflection, total-field ground magnetics, and resistivity to define the three-dimensional geometry and characteristics of poorly characterized recent fault strands. Locating the strongest magnetic and resistivity anomalies focused further surveys on the most potentially active fault strands. We used a sledgehammer seismic reflection profile to image faulted Cenozoic stratigraphy below the anomalies. The signal arising from each technique varies regionally among faults and locations so it is important to integrate methods. Combining electrical resistivity, ground magnetics, and high-resolution seismic imaging can identify the more recent and active strands within a fault zone. Such signatures have been found, by similar field campaigns, to occur on normal and strike-slip faults in other areas in the Great Basin including Warm Springs Valley, Pahrump Valley and the Virginia Range of Nevada. This combination of geophysical signatures provides an additional tool for paleoseismic investigations in the Great Basin and abroad. The implications of such a set of techniques include improved seismic hazard analyses, particularly on the outskirts of urban areas, and more efficient targeting of paleoseismic investigative trenches.