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Assessing the Accuracy of a Borehole-Controlled Velocity Model of Yucca Flat, Nevada Using Large N Seismic Data

Session: Explosion Seismology Applications and Advances [Poster]

Type: Poster

Date: 4/19/2021

Presentation Time: 11:30 AM Pacific

Description: 

With geologic data from over 950 boreholes, the Yucca Flat basin, residing on the Nevada National Security Site (NNSS), has excellent borehole control on stratigraphy. These data were used to create a Geologic Framework Model (GFM) of the basin. 188 of these boreholes have corresponding downhole seismic survey data which were used to determine average P-wave velocities of the geologic units. With the acquisition of five new active-source Large-N datasets in Yucca Flat, we can now quantitatively assess the accuracy of the seismic model previously controlled only by borehole data. To do this, for each of the five datasets, we subset the GFM to the region of interest and create a forward model of P-wave travel times for the GFM given the Large-N source-receiver geometries. We then compare the empirical Large N P-wave travel times to the GFM-derived travel times. We first make trial-and-error adjustments to the unit velocities (while keeping the layer geometry intact) to improve the travel time residuals. Updating the models in this way indicates that the borehole-controlled model overestimates alluvium velocities across Yucca Flat, and overestimates them in southeastern Yucca Flat. The trial-and-error method reduced the travel time error by a factor of five. We then implement a Bayesian grid search to more systematically determine optimal velocity models and provide uncertainty analysis. This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy. DOE/NV/03624--0962. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Presenting Author: Rhiannon E. Vieceli

Student Presenter: Yes

Authors