Estimating subsurface topography from surface-to-borehole seismic studies at the Rye Patch geothermal reservoir, Nevada, USA

A 3-D surface seismic reflection survey, covering an area of over 7.7 km2, was conducted at the Rye Patch geothermal reservoir (Nevada, USA) to explore the structural features that may control geothermal production in the area. In addition to the surface sources and receivers, a high-temperature three-component seismometer was deployed in a borehole at a depth of 1250 m within the basement below the reservoir, which recorded the waves generated by all surface sources. The objective of this study was to determine the subsurface structure of the reservoir based on this surface-to-borehole dataset. A total of 1959 first-arrival travel times were determined out of 2134 possible traces. Two-dimensional ray tracing was performed to simulate wave propagation from the surface sources to the receiver at depth. The ray tracing was based on a 2-D laterally homogeneous velocity model derived from results of a verticalseismic- profile (VSP) experiment recorded in the same well. The method is an approximation where it is assumed that differences in travel time between the observed and modeled data are caused by structural deviations from a homogeneously layered model as estimated by the VSP profile, and thus are mapped into topographic changes at depth. The results indicate, to first order, the presence of two dominant geologic features. The first observation is consistent with the regional trend of the geologic units in the Basin and Range province with a north-south strike and dip to the west, as expected for this area west of the Humboldt Thrust Range. The second is a local feature in the form of an east–west ridge. The geometry of the structure is corroborated by results from a seismic-reflection survey, and by results of a gravity survey conducted in the area above the reservoir. # 2003 CNR. Published by Elsevier Science Ltd. All rights reserved.