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Investigations of Fracture Zones in Crystalline Rock by Borehole Radar

Published online by Cambridge University Press:  28 February 2011

Olle Olsson ,
Lars Falk ,
Olof Forslund ,
Lars Lundmark  and
Eric Sandberg
Olle Olsson
Affiliation:
Swedish Geological Company, Box 1424, S-751 44 Uppsala, Sweden
Lars Falk
Affiliation:
Swedish Geological Company, Box 1424, S-751 44 Uppsala, Sweden
Olof Forslund
Affiliation:
Swedish Geological Company, Box 118, S-930 70 Malå, Sweden
Lars Lundmark
Affiliation:
Swedish Geological Company, Box 118, S-930 70 Malå, Sweden
Eric Sandberg
Affiliation:
Swedish Geological Company, Box 1424, S-751 44 Uppsala, Sweden
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Abstract

A borehole pulse radar system has been developed as part of the International Stripa Project with the objective to identify and characterize fracture zones at a considerable distance from boreholes. The radar uses very short pulses, which are transmitted and received by dipole antennas inserted into the boreholes. The pulses are extremely broadband with center frequencies of 25–60 MHz corresponding to wavelengths of a few meters in the rock. At 25 MHz the attenuation in the Stripa granite is 28 dB/100 m and the pulse velocity is approximately 128 000 km/s. Reflection measurements have been used to identify fracture zones and determine their position and orientation. The zones often cause strong and well-defined reflections. Improvements in the pulse form and numerical filtering of the data have consequently made the radar a very efficient instrument for locating fracture zones. During measurements in Stripa reflections from fracture zones have been observed more than 100 m from the borehole.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 50: Symposium STOCKHOLM – Scientific Basis for Nuclear Waste Management IX , 1985 , 145
Copyright
Copyright © Materials Research Society 1985

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References

1. Olsson, O. and Sandberg, E., Crosshole investigations – Preliminary design of a new borehole radar system. Stripa Project, IR-84−04, SKB, Stockholm, 1984.Google Scholar
2. Carlsten, S., Magnusson, K.-Å., Olsson, O., Crosshole investigations - Description of the small scale site. Stripa Project, IR-85−05, SKB, Stockholm, 1985.Google Scholar
3. Ivansson, S., Cross-hole investigations - Tomography and its application to crosshole seismic measurements. Stripa Project, IR-84-O8, SKB, Stockholm, 1984.Google Scholar