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Use of multi-offset borehole-radar reflection method in fractured crystalline bedrock at Mirror Lake, Grafton County, New Hampshire

December 31, 1998

Multi-offset, single-hole, borehole-radar reflection surveys were conducted at the U.S. Geological Survey Fractured Rock Research Site at Mirror Lake, in Grafton County, New Hampshire. The study was conducted to evaluate the benefits of applying multi-offset seismic processing techniques to borehole-radar reflection surveys in fractured rock.

The multi-offset reflection surveys were conducted in conjunction with a saline tracer- injection experiment. During injection, a sodium chloride (NaCl) solution was continuously pumped into a hydraulically conductive zone that was isolated by specially constructed, reusable, PVC straddle packers suspended from PVC casing. Eight common-offset borehole reflection profiles were collected within the PVC-sleeved portion of the borehole before and during the tracer injection. The offset between the transmitter and receiver antennas ranged from 6.4 to 9.9 m (meters). The common offset data were filtered, sorted into common distance-point (CDP) gathers, normal move-out (NMO) corrected, and stacked to produce a zero-offset borehole CDP profile.

Comparison of the common-offset and CDP profiles indicates that multi-offset data acquisition and CDP processing; (1) increases the resolution of reflectors near the borehole, (2) decreases the effects of direct wave coupling, antenna ringing, and system noise, and (3) improves the clarity of difference images used to identify the effects of saline tracer on reflections from transmissive fractures.

Citation Information

Publication Year 1998
Title Use of multi-offset borehole-radar reflection method in fractured crystalline bedrock at Mirror Lake, Grafton County, New Hampshire
Authors John W. Lane, F. P. Haeni, Roelof J. Versteeg
Publication Type Conference Paper
Publication Subtype Conference Paper
Index ID 70206374
Record Source USGS Publications Warehouse
USGS Organization Office of Ground Water

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