POTENTIAL FIELD ANALYSIS OF PORTIONS OF THE WALKER LANE BELT/EASTERN CALIFORNIA SHEAR ZONE, EAST-CENTRAL CALIFORNIA AND WEST-CENTRAL NEVADA

We are currently extending our regional analysis of the structure of the northern portion of the Walker Lane Belt and Eastern California Shear Zone utilizing gravity inversions based both on national gravity compilations and new detailed gravity datasets from areas such as Queen Valley (recently acquired by KU) and Fish Lake Valley (Black, et al., 2004). The area is dominantly a right-lateral strike-slip tectonic regime currently accounting for approximately 25% of the shear displacement budget of the NA/Pacific Plate boundary. However, in the area of the Mina deflection there is a change in the strain field causing a complex array of NW-striking dextral faults, NW-striking and NE-striking normal faults, and ENE-striking sinistral faults. Inversion of gravity data in the area allows interpretation of basin fill geometries, bedrock structure, and tracing of lithological units beneath basin fill. Three dimensional gravity models help in developing a three dimensional picture of the subsurface, including fault geometries and sedimentary geometries. Understanding these are key to the development of realistic regional strain budgets and sedimentation patterns, which in turn are important in the study of tectonic rates in complex areas. Due to the non-unique nature of gravity modeling the vertical extent of features are poorly constrained. The models are still quite useful if standardized on a regional basis. In the case of the basin depth problem this is usually done in the Basin and Range by assuming a standard basin density/depth model (i.e. Jachens and Moring, 1990). Using the data for absolute rate calculations requires hard data such as deep, basement-penetrating borehole samples and log suites. Borehole information and seismic information are being utilized where available. In addition, we are experimenting with joint inversions utilizing the 2002 national aeromagnetic grid and detailed individual aeromagnetic survey flightline data.