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Open-File Report 2015–1019

Obtaining Valid Geologic Models from 3-D Resistivity Inversion of Magnetotelluric Data at Pahute Mesa, Nevada

By Brian D. Rodriguez and Donald S. Sweetkind

Thumbnail of and link to report PDF (20.7 MB)Abstract

We summarize the results of a three-dimensional (3-D) resistivity inversion simulation that we conducted with the intent of characterizing the subsurface 3-D distribution of volcanic composite units of Pahute Mesa, Nevada, without any a priori information on the actual 3-D distribution of the known subsurface geology. The 3-D methodology involved using a 3-D geologic model based on drillhole data and average electrical resistivities of the key hydrostratigraphic units at Pahute Mesa to create a 3-D resistivity forward (“known”) model that depicted the subsurface resistivity structure expected for the input geologic configuration. The calculated magnetotelluric response of the modeled resistivity structure was then assumed to represent observed magnetotelluric data and was used as input into a 3-D resistivity inverse model that was allowed to iteratively estimate in 3-D without any a priori geologic information, in particular, the thickness and resistivity of the volcanic composite units. The resulting 3-D resistivity inversion simulation was compared to the “known” model and the results evaluated.

The 3-D inversion was generally able to reproduce the gross resistivity structure of the “known” model, but the simulated conductive volcanic composite unit horizons were often too shallow when compared to the “known” model. Additionally, the chosen computation parameters such as station spacing appear to have resulted in computational artifacts that are difficult to interpret but could potentially be removed with further refinements of the 3-D resistivity inversion modeling technique.

First posted February 27, 2015

For additional information, contact:
Director, Crustal Geophysics and Geochemistry Science Center
U.S. Geological Survey
Box 25046, MS 964
Denver, CO 80225
http://crustal.usgs.gov/

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Suggested citation:

Rodriguez, B.D., and Sweetkind, D.S., 2015, Obtaining valid geologic models from 3-D resistivity inversion of magnetotelluric data at Pahute Mesa, Nevada: U.S. Geological Survey Open-File Report 2015–1019, 104 p., https://dx.doi.org/10.3133/ofr20151019.

ISSN 2331-1258 (online)



Contents

Abstract

Introduction

Electrical Properties of Rock

Magnetotelluric Method

3-D Resistivity Model Build

3-D Resistivity Inversion Results

Conclusion

Acknowledgments

References Cited

Appendix 1. Magnetotelluric Simulated and Computed Data


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