Abstract

Specially designed refraction microtremor (ReMi) surveys assessed shear‐wave velocities beneath the deepest portion of the Reno‐area basin, as defined by gravity assessments. The analyses delineated sedimentary basin thicknesses (depths to VS=2.2  km/s or Z2.2) of up to 900 m, as well as further details of the deep‐basin velocity structure. Velocity models extended down to 1500 m. Deployment of 30 stand‐alone wireless instruments, across arrays 2.9–5.8 km long, achieved these results by recording ambient urban noise. Two parallel east–west arrays and one shorter north–south array recorded microtremor noise on separate days, for two hours each. ReMi data analysis characterized and mapped the velocity structure beneath the arrays from these noise records. Analyses from overlapping subsets of instruments along each array produced a series of 1D velocity–depth profiles. Interpolation of the 1D velocity–depth profiles yields a 2D representation of the deep shear‐wave velocity structure of the basin. Of particular interest was the observation of a 300–350 m vertical offset in the basin floor, defining the location of either a fault or a paleoerosion surface. This study demonstrates that the ReMi shear‐wave velocity characterization technique is capable of velocity constraint to depths greater than 1000 m. ReMi is thus a valuable tool for delineating deep‐basin structure, shear‐wave velocity, and the identification of faults beneath urban regions. These efforts contribute basin details toward the development of the western Basin and Range Community Velocity Model and the Reno–Tahoe urban hazard map.

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