Institute of Geophysics of the CAS, v. v. i.

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Microgravimetry

Microgravimetry

Microgravity investigations are carried out in order to solve various problems of engineering geology, mainly location of voids and their monitoring. Very detailed measurements of high accuracy can indicate voids of any origin, provided the size and depth are large enough to produce gravity effect stronger than is the level of confidence of relevant gravity signal. The resolution of our LaCoste&Romberg Model D gravimeter is 1 microGal (10-8 m/s2).

For example, we conducted a microgravity survey on a construction site of an underground tunnel in a coal mine district. During construction work an anchor was drilled through a void, the existence of which was not expected at the site. However, our survey indicated a few more locations suspected as old mining voids. The follow-up test drilling confirmed the existence of voids and provided a basis for technological changes in further construction process. We also carried out a few surveys that located hazardous site in historical centres of the cities (Prague, Brno and Ostrava).

A special case is represented by our microgravity investigation applied to archaeology. Successful survey was performed in the St. Vitus cathedral in the Prague Castle. In front of the altar a negative gravity anomaly delineated the presence, and even the shape of the original tomb of the King Charles IV. (14th century). A video-camera suspended through a small-scale drillhole afforded a detailed view of the inner space of the tomb. Similar investigations were performed in the Valley of the Kings in Luxor, where a few indications of tombs were observed in microgravity data.

Researcher: Jan Mrlina               Cooperation:
ElSayed Issawy (NRIAG, Egypt)

Microgravity investigation inside the St. Vitus cathedral,
Prague Castle.

References cited:
Blecha, V., Mrlina J., (2001): Microgravity prospecting for the voids in an abandoned coal-working field. - Proceedings of 7th Meeting of EEGS, Birmingham, England, p. 134-135.
Issawy, E.A, Tealeb, A.A., Mrlina, J., Radwan, A.H., Hassan, G.S. and Sakr, K.O. (2001): Micro-gravity studies in archaeo-prospecting of the Valley of the Kings, Luxor, Egypt. - Bulletin (NRIAG), Geophysics (B), Cairo, 201-212.
Mrlina, J. (2001): 4D microgravimetry in geoengineering. – Extended Abstracts, 63rd EAGE Conference, Amsterdam, 11-15 June, 2001, V1, IG5, 1-4.
Mrlina, J. (2002): Microgravimetric investigations of geomechanical phenomena and processes. – In: Engineering Geology for Developing Countries – Proc. 9th Congress IAEG (J.L.van Rooy and C.A. Jermy, Edit.), Durban, South Africa, 2002, 1230-1235.
Mrlina, J., Křivánek, R., Majer, A. (2005): Geophysical investigation for the location of tombs in the St. Vitus Cathedral in Prague. – Castrum Pragense, 6, 105-124. (in Czech, English abstract).