Optimized Velocities and Prestack Depth Migration in the Reno-Area Basin

Optimized Velocities and Prestack Depth Migration in the Reno-Area Basin, Figure 2 Figure 2.
Depth section 2.3 km long extending to 1000 m depth, running west (left) to east (right) along the Truckee River through downtown Reno. No vertical exaggeration. Colors indicate velocities optimized from 1st-arrival picks, with Quaternary gravels (green) overlying Tertiary sands (red). The reflections are interpreted as showing two west-dipping normal faults (blue lines).
We collected seismic reflection profiles in the Reno, Nevada area basin in collaboration with the USGS and nees@UTexas during June 2009. Stratigraphic horizons and vertical offsets associated with faulting appear along a 6.72 km Truckee River profile while strong, horizontally propagating body waves are seen in shot gathers from the southern 3.84 km Manzanita Lane profile (fig. 1). Reno-area basin fill overlies Miocene andesitic volcanic rocks and consists of Neogene sedimentary rocks and Quaternary outwash deposits. Using the seismic shot records, we created optimized velocity models of the Reno basin using commercial SeisOpt®@2DTM software. The refracted P-wave arrivals provide inputs for a global velocity model over the length of the profiles and to a depth proportional to the source offset distances, expected to be 150-200 m. Within this basin most of the lateral velocity heterogeneity appears within 200 m of the surface. Comparing this velocity model to stacked sections produced by the USGS added confidence to the interpretations of strong reflection boundaries seen in the seismic sections (fig. 2). Boundaries in the velocity model coincide with prominent reflection boundaries as well as with known depths of volcanic fill and other deposits, constraining their depths and velocities. The tomographic velocity sections were then used as input with the shot records to a Kirchhoff pre-stack depth migration (PSDM) imaging steeply dipping structure and further constraining current interpretations and fault/basin geometry. The PSDM resolved the cause of the horizontally propagating waves seen along Manzanita Lane as sidewall reflections from a steeply dipping fault (fig. 3).
</p><p>Acknowledgements: Research supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award numbers G09AP00051, 08HQGR0015, and 08HQGR0046. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.</p>


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