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High-Resolution Bayesian Spatial Auto-Correlation (Spac) Pseudo-3D vs Model of Utah Forge Site With a Dense Geophone Array

Session: Advances in Upper Crustal Geophysical Characterization II

Type: Oral

Date: 4/21/2021

Presentation Time: 02:00 PM Pacific

Description: 

The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) project aims to establish an enhanced geothermal systems (EGS) laboratory to develop and test new technologies that improve geothermal energy extraction from low-permeability host rocks. In support of the FORGE project, a high-resolution three-dimensional (3D) basin-scale velocity model is required to: (1) improve seismic event locations, (2) improve ground motion predictions for seismic hazard analysis, and (3) provide additional constraints on the uplift of the Mineral Mountains and resulting structures and the formation of the adjacent basin. Spatial autocorrelation (SPAC) methods use the noise field to construct coherent surface waves in the frequency domain and are typically applied to resolve one-dimensional (1D) shallow Vs structure (e.g. upper 30 meters) at individual sites. Here, we expand the application of SPAC from typical 1D Vs profiles to pseudo-3D imaging via Bayesian Monte-Carlo inversion (BMCI) using a dense nodal array (49 nodes) located at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) site. Using combinations of 4 and 9 geophones in subarrays provides for 36 and 25 1D Vs profiles, respectively. Profiles with error bars are determined by calculating coherency functions that fit observations in a frequency range of 0.2–5 Hz. Thus, a high-resolution pseudo-3D Vs model from the surface to 2.0 km depth is derived and shows that surface-parallel sedimentary strata deepen to the west, consistent with a 3D seismic reflection survey. Moreover, the resulting Vs profile is consistent with a Vs profile derived from distributed acoustic sensing (DAS) data located in a borehole at the FORGE site. The pseudo-3D velocity model shows that the base of the basin dips ~22^o to the west and topography on the basement interface coincident with the Mag Lee Wash suggests that the bedrock interface is an unconformity.

Presenting Author: Hao Zhang

Student Presenter: No

Authors