Seismic Techniques

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Exploration Technique: Seismic Techniques

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Seismic Techniques
Parent Exploration Technique: Geophysical Techniques
Information Provided by Technique
Lithology: Rock unit density influences elastic wave velocities.
Stratigraphic/Structural: Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc.
Hydrological: Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation.
Thermal: High temperatures and pressure impact the compressional and shear wave velocities.
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Seismic Techniques:
Seismic methods provide information regarding the elastic properties of the subsurface through the measurement of the propagation velocity of elastic waves.
Other definitions:Wikipedia Reegle



 
Use in Geothermal Exploration
Seismic techniques are used in geothermal exploration in a wide variety of applications, ranging from regional exploration for a heat source to determining locations of individual fractures.[1]

See Reflection Survey; Refraction Survey; Micro-Earthquake; Teleseismic-Seismic Monitoring







 
Physical Properties
Seismic waves are classified as elastic waves because they cause nonpermanent deformation to the material through which they propagate. The characteristics of the deformation define the wave type.[2]

The fundamental wave types for seismic surveys are the p-wave (a.k.a. longitudinal, compressional) and the s-wave (a.k.a. transverse or shear). The particle movement of a p-wave is in the direction of wave travel and involves compression and expansion. For an s-wave, the particle movement is perpendicular to the direction of wave travel.
Compression and shear wave particle motion and direction of propagation.[3]


Velocity is the physical parameter measured by seismic techniques. Seismic waves propagate through a rock body at a velocity which is governed by the elastic properties (stress and strain, Young's modulus) and density of the geological formation.[2] Additional factors which influence compressional and shear wave velocities are lithology, extent of fractures, temperature, fluid content, saturation, and fluid pressure in the subsurface.[2][4]Empirical ranges of compressional and shear wave velocities through different lithologies are shown in the figure below.[5]

Typical rock velocities.[5]
Acoustic impedance contrasts are the ‘reflectors’ which are mapped using seismic techniques and may represent changes in lithology or discontinuous geological contacts. The acoustic impedance is defined as the product of the density and p-wave velocity within a rock unit. When an elastic wave encounters an acoustic impedance boundary, a portion of the wave energy is reflected off of the boundary and a portion is refracted into the second medium, according to Snell’s Law as depicted in the figure below.[4][6]

Behavior of a compressional elastic wave at an acoustic impedance boundary[7]











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      Document # Analysis
      Type
      Applicant Geothermal
      Area
      Lead
      Agency
      District
      Office
      Field
      Office
      Mineral
      Manager
      Surface
      Manager
      Development
      Phase(s)
      Techniques
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      DOI-BLM-NV-W030-2010-0021-CX CX US Geothermal Inc San Emidio Desert Geothermal Area Bureau of Land Management BLM Winnemucca District Office Bureau of Land Management Bureau of Land Management Geothermal/Exploration Seismic Techniques
      DOI-BLM-NV-W030-2011-0007-CX CX US Geothermal Inc San Emidio Desert Geothermal Area BLM BLM Winnemucca District Office BLM BLM Geothermal/Exploration Seismic Techniques
      DOI-BLM-OR-P000-2010-0003-EA EA Davenport Power LLC Newberry Caldera Geothermal Area BLM BLM Prineville District Office BLM United States Forest Service Geothermal/Exploration Drilling Techniques
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      Seismic Techniques
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      Seismic Techniques


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