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Constraining Geologic Structure of the Rock Valley Fault Zone: Dense Gravity Analysis for the Rock Valley Direct Comparison Experiment

Description: 

Direct comparisons of seismic wave observed from earthquake and explosion sources through similar geologic structure are sparsely available. Discriminating the signals produced by shallow earthquakes versus explosions is thus challenging. The Rock Valley Direct Comparison experiment addresses this by proposing to record explosive sources collocated with historic shallow earthquakes. To understand the historic data and to directly compare the signals requires a detailed characterization of the underlying geologic structure. A Geologic Framework Model (GFM) of the Rock Valley region has been generated with data inputs from regional gravity surveys. However, these regional surveys are sparse compared to the scale of the study region. To improve our GFM and better understand the underlying fault structure, we collected a densely sampled gravity dataset spanning Rock Valley Fault Zone (RVFZ). We took gravity measurements along 5 fault perpendicular lines totaling 218 sites, including reoccupation of several regional sites, with ~150 m spacing, and 200-700 m separating each line. Relative gravity measurements are calibrated to an absolute gravity station south of RVFZ in Mercury, Nevada. Gravity data corrections are applied including instrumental drift, latitude, tide, terrain, free air, and Bouguer corrections. The resulting Bouguer anamoly maps clearly highlight the RVFZ structure with gravity lows in the center of the valley where alluvium fill is thickest and gravity highs on the flanks where Paleozoic sedimentary units and Tertiary volcanic rocks are exposed. We run a series of froward models to test the validity of various fault zone permutations and the ability of the data to constrain such models. The gravity observations are also compared to recent tomographic inversions. The seismic data from the region will be integrated with the gravity information in a joint inversion as a part of future work on the project. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Session: Crustal Imaging of High Seismic Hazard Regions [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Miles Bodmer

Student Presenter: No

Invited Presentation: 

Authors