Updated Gravity Anomaly Map of the Reno Basin
AdvisorLouie, John N.
Geological Sciences and Engineering
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The Truckee-Meadows is a sedimentary basin, with bedrock possibly hundreds of meters below. Gravimetry provides an estimate of depth-to-bedrock because lighter, less-dense sediment pulls less on gravimeters, while bedrock pulls more. Accurate estimates of depth-to-bedrock are necessary for models of seismic shaking because sediment and bedrock move and act differently when in contact with earthquake energy. Comparing recent studies such as Abbott and Louie (2000) and Cashman et al. (2012) displays differences of up to 300 meters in estimating the depth-to-bedrock. An updated gravity anomaly map provides accurate data by combining 356 gravity stations, and may resolve these issues. Gravity measurements are made using a gravimeter to demonstrate changes in gravity across different areas. Gravity varies due to elevation, tidal changes, local topography, and regional terrain. The variations in gravity can be corrected for using the drift correction, terrain correction, free-air correction, and Bouguer correction. Respectively, these corrections account for the drift of instrument and tidal variations (such as the varying pull of the sun and the moon), the pull of mountainous areas or lack-of-pull of basins, elevation, and the slab of material between the gravity measurement station and a datum surface at sea-level. Along with the difference between observed and theoretical gravity at different latitudes, these corrections are combined to create the complete Bouguer anomaly. The Pan-American Center for Earth and Environmental Studies database, University of Nevada, Reno (UNR) Applied Geophysics class data, and raw data from Abbott and Louie (2000) are combined to create an updated complete Bouguer anomaly map of the Reno, Nevada area basin. UNR class data are re-corrected, and outer ring terrain corrections (to account for pull/lack of pull of regional terrain up to 166 kilometers away) are added to both Abbott and Louie and class data to calculate the complete Bouguer anomaly at each point. The data are then inte