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The use of microgravity for cavity characterization in karstic terrains

P. Styles, R. McGrath, E. Thomas and N. J. Cassidy
The use of microgravity for cavity characterization in karstic terrains
Quarterly Journal of Engineering Geology and Hydrogeology (May 2005) 38 (2): 155-169

Abstract

Microgravity is the interpretation of changes in the subsurface density distribution from the measurement of minute variations in the gravitational attraction of the Earth. As a technique, it is particularly suited to the investigation of subsurface structures, mapping of geological boundaries and, most importantly in this case, the location and characterization of voids or cavities. Gravity variations due to the geological/petrophysical changes associated with fracturing and changes in pore composition are superimposed upon much larger variations due to elevation, latitude, topography, Earth tides and regional geological variations. However, these external changes can be modelled or monitored with sufficient accuracy to be removed from the data. With the recent development of high-resolution instruments, careful field acquisition techniques and sophisticated reduction, processing and analysis routines, anomalies as small as 10 microgal can be detected and interpreted effectively. This paper describes the "state-of-the-art" application of the microgravity technique for the detection and characterization of karstic cavities in a variety of limestone terrains, including the Carboniferous Limestone of the United Kingdom and Eire and the coral limestones of the Bahamas. The case study examples show how the recorded gravity anomalies have revealed the location of density variations associated with underground cave systems and, ultimately, provided information on their depths, shapes and morphology from a combined analysis of their spectral content, characteristic gradient signatures and modelling responses. In addition, mass deficiencies have been estimated, directly from the anomaly map, by the use of Gauss's theorem without any prior knowledge of the exact location, or nature, of the causative bodies.


ISSN: 1470-9236
EISSN: 2041-4803
Coden: QJEGA7
Serial Title: Quarterly Journal of Engineering Geology and Hydrogeology
Serial Volume: 38
Serial Issue: 2
Title: The use of microgravity for cavity characterization in karstic terrains
Affiliation: Keele University, School of Earth Sciences and Geography, Keele, United Kingdom
Pages: 155-169
Published: 20050501
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 25
Accession Number: 2005-062399
Categories: GeomorphologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
N20°45'00" - N28°00'00", W79°30'00" - W72°00'00"
N51°22'60" - N51°51'00", W04°19'60" - W03°04'60"
N51°30'00" - N55°19'60", W10°30'00" - W06°30'00"
Secondary Affiliation: Geotechnology, GBR, United Kingdom
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 200538
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