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Origin of the anomalies of gravity and its vertical gradient over cavities in brittle rockNormal access

Author: Z. Fajklewicz
Journal name: Geophysical Prospecting
Issue: Vol 34, No 8, December 1986 pp. 1233 - 1254
DOI: 10.1111/j.1365-2478.1986.tb00526.x
Organisations: Wiley
Language: English
Info: Article, PDF ( 978.42Kb )

Summary:
Investigations show that the depth range of the gravity method for detecting cavities is considerably greater than expected on the basis of theoretical calculations that consider only the depth and shape of the cavity.

The cavity generates its own gravity field that is the sum of the activity of the cavity itself and the density changes caused in the surrounding rocks by the process of their destruction as a result of the cavity's expansion. The latter factor is decisive for the cavity's detection by the gravity method in several cases.

The extent of the zones of change density in the surrounding rocks and their actual shape depend on many parameters. Thus, the determination of the depth of the cavity cannot be made by comparing measured and theoretical curves of gravity anomalies. The location of the center of gravity of the area disturbed by the cavity or upper boundary of its development towards the ground surface can be determined by denoting the singular point of gravity as a result of the downward analytical continuation of Ag.

The Strakhov-Grigorieva-Lapina (1977) method fulfils the necessary conditions in the field.


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