Graduation Year

2024

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geosciences

Major Professor

Paul Wetmore, Ph.D.

Co-Major Professor

Charles Connor, Ph.D.

Committee Member

Glenn Thompson, Ph.D.

Committee Member

Elisabeth Gallant, Ph.D.

Keywords

basin geometry, education, geophysics, gravimetry, modeling, potential fields

Abstract

Gravity data and modeling can be used to create a 3D view of basin and fault geometries, a valuable tool for seismic hazard assessment. Additionally, access to a high-speed, easy-to-use modeling workflow will enable more researchers to supplement their work with a new method and allow students to be exposed to modeling earlier in their academic careers. The primary goals of this work are to create a widely usable 3D gravity and basin model, to create an introduction to modeling teaching module for undergraduate geology students, and to apply the model to the northernmost two segments of the Lost River Fault in Idaho to constrain its dip and the sediment thickness of the overlying basin.

The model is written in Python, which is popular among geoscientists for being versatile, beginner-friendly, and open-source. It uses several powerful libraries, including pandas for importing and organizing data, PyGMT for producing maps, and multiprocessing to decrease runtime by a factor of ~2-8. The model reads a comma-separated values (CSV) file containing the UTM coordinates and Bouguer gravity anomaly values, and the user configures parameters within a separate parameter file, such as grid spacing and density contrast. Without any further input from the user, the code will generate several gravity maps, a sediment thickness map, and a basin floor slope map. It will also create a directory structure for saving the modeled data and figures to minimize the work required by the user before running the model. The ease of use and high speed make this a valuable tool for researchers and for introducing students in courses such as structural geology or geophysics to modeling with Python. The user can test different parameters and quickly compare the results to learn how the model is affected by each.

I apply this model to the northern Lost River Fault with an assumed density contrast of -450 kg/m3 between the Quaternary alluvium basin fill and Paleozoic basement rock. The modeled basin sediment thickness varies rapidly over short distances with steep gradients along the basin-bounding faults and in the middle of the valley. This pattern suggests that the basin floor retains paleotopographic features and that there are buried Eocene Challis Volcanics with densities similar to those of the sediment fill, as evidenced by exposures at the surface.

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