Comparing Deformation at Soda Lake Geothermal Field from GPS and 3D Seismic
AuthorKent, Tyler J.
Geological Sciences and Engineering
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The transition between the two distinct structural regimes of the Walker Lane and the Basin and Range allows for complex transtensional fault interactions. The Carson Sink is the surface expression of the interaction of shear and extensional strains that cause both crustal extension and block rotation. This study investigates this tectonic shift at the Soda Lake geothermal field by comparing the direction and rate of deformation from both regional GPS and a 34 sq km 3D seismic survey. The GPS stations in the region estimate the strain field by comparing tensor solutions that show changing direction and magnitude of strain across the Carson Sink. Using stations surrounding the Soda Lake 3D seismic survey, the strain tensor produced is comparable in orientation to Basin and Range strain but has larger magnitudes. To quantify deformation within the Soda Lake 3D seismic survey, we calculate fault dip and offset of a deformed paleo-planer lacustrine mudstone. Plotting the mean dip direction of the faults in the seismic reflectivity, matches the mean surrounding GPS extensional direction, suggesting fault displacement is likely to be normal dipslip. Using a minimum age of 0.51 Ma from nearby sedimentation rates, the measured extension across the 5.4 km length of this study has a rate of 0.19 mm/yr. This is quite a high value for Basin and Range extension and it is likely a result of some influence from the Northern Walker Lane. The lack of an obvious piercing point for shear observed within the seismic volume precludes a clear estimate of strike-slip related motion within the Soda Lake 3D seismic survey. Clear extension and a large fault bend, indicates a localized relay ramp model. With focused extension indicated by two late Quaternary extrusive volcanic bodies, a model of a transtensional pull-apart basin is also considered. Given the few mapped intrabasinal faults at the surface, this study gives a unique view into fault offsets inside the Carson Sink.