NOTE: This item is not available outside the Texas A&M University network. Texas A&M affiliated users who are off campus can access the item through NetID and password authentication or by using TAMU VPN. Non-affiliated individuals should request a copy through their local library's interlibrary loan service.
Controlled-source electromagnetic mapping of a faulted sandstone aquifer in central Texas
MetadataShow full item record
Controlled-source electromagnetic mapping (CSEM) techniques were used to identify lateral variations in electrical conductivity associated with faults and facies contacts in a shallow sandstone aquifer in central Texas. The purpose of the research is ultimately hydrologic in nature, for faulting often plays a significant role in affecting groundwater flow. The affect of lithology, structural geology and the role of the faults in this aquifer has been previously studied by Randolph and Johnson (1989) and Randolph (1991). Results indicate that the CSEM technique provides complementary subsurface structural information that can be used to refine hyrological models and their interpretation for local water resources management and conservation. In this study frequency--domain (FEM) and time-domain electromagnetic (TEM) surveys were Geonics 34-3 system, with which conducted. The frequency-domain instrument utilized was a Geonics 34-3 system, with which apparent conductivity values were collected in multiple traverses over a variety of facies changes and fault contacts. This portion of the research was conducted not only to identify subsurface lateral variations but also to test how useful this particular system is as a mapping tool and what its limitations are. The Geonics 34-3 system clearly resolves lateral electrical conductivity variations in the internal sandstone units, but it is difficult to differentiate between the apparent conductivity signatures of facies changes and fault contacts. The system has a high noise level, therefore if a traverse passes over particularly resistive material, for instance the Lower Hickory which is less than the 0.002 S/m detection limit, all the system can detect is noise. To test the ability of the time-domain survey and to identify subsurface structure and stratigraphy at the study site two time-domain electromagnetic profiles were conducted with the Geonics PROTEM 47 system. An Occam-style regularized inversion written by Mark Everett which finds the 1-D smoothest model that fits the data to a tolerable misfit was used to model the data. The individual 1-D models were linked together to create a vertical conductivity cross-section of the subsurface. The final modeled conductivity values range from extremely resistive to abnormally high conductive values across very small vertical and lateral distances. The time-domain profiles proved difficult to analyze suggesting that the subsurface geology is strongly 3-D at the study site.
DescriptionDue to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to firstname.lastname@example.org, referencing the URI of the item.
Includes bibliographical references: p. 44-45.
Issued also on microfiche from Lange Micrographics.
Gorman, Erin Margaret (1998). Controlled-source electromagnetic mapping of a faulted sandstone aquifer in central Texas. Master's thesis, Texas A&M University. Available electronically from
Request Open Access
This item and its contents are restricted. If this is your thesis or dissertation, you can make it open-access. This will allow all visitors to view the contents of the thesis.