Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations

Beem, L I

Title: Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations

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Abstract

The use of the perturbation of seismic wave velocities by solid earth tides as a possible method of exploration for fractured media is discussed. Velocity of compressional seismic waves in fractured homogeneous rock has been observed to vary through solid earth tide cycles by a significant 0.5-0.9%. This variation of seismic velocities may be attributed to the opening and closing of joints by tidal stresses. In an attempt to see if shear-wave velocities show a similar velocity variation, a pneumatic shear-wave generator was used for the source. The 5 receivers, 3-component, 2.0 Hz, moving-coil geophones, were connected to a GEOS digital recorder. The two receivers located 120 m and 110 m from the source showed large shear-to-compression amplitude ratio and a high signal-to-noise ratio. A glaciated valley was chosen for the experiment site, since topography is flat and the granodiorite is jointed by a set of nearly orthogonal vertical joints, with superimposed horizontal sheeting joints. A slight velocity variation was noted in the first 200 consecutive firings; after which, the amplitude of the shear-wave begun to increase. This increase has been attributed to the compacting of the soil beneath the shear-wave generator (SWG). In the future, the soil will bemore »« less

Authors:: Beem, L I

Publication Date:: Sat Aug 01 00:00:00 EDT 1987

Research Org.:: Idaho State Univ., Pocatello

OSTI Identifier:: 5697055

Report Number(s):: CONF-870915-
Journal ID: CODEN: AABUD

Resource Type:: Conference

Journal Name:: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

Additional Journal Information:: Journal Volume: 71:8; Conference: American Association of Petroleum Geologists Rocky Mountain Section meeting, Boise, ID, USA, 13 Sep 1987

Country of Publication:: United States

Language:: English

Subject:: 02 PETROLEUM; 03 NATURAL GAS; NATURAL GAS DEPOSITS; EXPLORATION; PETROLEUM DEPOSITS; SEISMIC SURVEYS; DATA ANALYSIS; FRACTURED RESERVOIRS; GEOLOGIC FRACTURES; PERMEABILITY; GEOLOGIC DEPOSITS; GEOLOGIC STRUCTURES; GEOPHYSICAL SURVEYS; MINERAL RESOURCES; RESOURCES; SURVEYS; 020200* - Petroleum- Reserves, Geology, & Exploration; 030200 - Natural Gas- Reserves, Geology, & Exploration

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                    Beem, L I. Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations.  United States: N. p., 1987. 
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                    Beem, L I. Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations.  United States.

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                    Beem, L I. 1987.  
        "Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations".  United States.

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@article{osti_5697055,

  title        = {Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations},

  author       = {Beem, L I},

  abstractNote = {The use of the perturbation of seismic wave velocities by solid earth tides as a possible method of exploration for fractured media is discussed. Velocity of compressional seismic waves in fractured homogeneous rock has been observed to vary through solid earth tide cycles by a significant 0.5-0.9%. This variation of seismic velocities may be attributed to the opening and closing of joints by tidal stresses. In an attempt to see if shear-wave velocities show a similar velocity variation, a pneumatic shear-wave generator was used for the source. The 5 receivers, 3-component, 2.0 Hz, moving-coil geophones, were connected to a GEOS digital recorder. The two receivers located 120 m and 110 m from the source showed large shear-to-compression amplitude ratio and a high signal-to-noise ratio. A glaciated valley was chosen for the experiment site, since topography is flat and the granodiorite is jointed by a set of nearly orthogonal vertical joints, with superimposed horizontal sheeting joints. A slight velocity variation was noted in the first 200 consecutive firings; after which, the amplitude of the shear-wave begun to increase. This increase has been attributed to the compacting of the soil beneath the shear-wave generator (SWG). In the future, the soil will be compacted prior to placing the SWG or the SWG will be coupled directly to the rock to alleviate the amplitude fluctuation problem. This research may have application in exploration for fracture permeability in the rock mass between existing wells, by measuring seismic velocities from well to well through the tidal cycle.},

  doi          = {},

  url          = {https://www.osti.gov/biblio/5697055},
  journal      = {AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)},
number       = ,

  volume       = 71:8,

  place        = {United States},

  year         = {Sat Aug 01 00:00:00 EDT 1987},

  month        = {Sat Aug 01 00:00:00 EDT 1987}

}

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