Passive Seismic Techniques

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Exploration Technique: Passive Seismic Techniques

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Seismic Techniques
Parent Exploration Technique: Seismic 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.
Passive Seismic Techniques:
Passive seismic techniques utilize vibrations from natural earthquakes or rupture processes (due to hydraulic stimulation) as a source for structural imaging of the subsurface.
Other definitions:Wikipedia Reegle

The aim of passive seismic methods is to determine the hypocenter of earthquake and rupture microseismic events in order to image seismically active faults or locate fracture systems in the subsurface.[1]
Use in Geothermal Exploration

Field Procedures
Passive seismic techniques generally require that a sufficiently dense monitoring array of seismometers are installed in the vicinity of a geothermal reservoir with a typical recording duration of a few months.[1] The survey design (in terms of required instrument sensitivity and seismometer array geometry) depend on the subsurface properties and the anticipated frequency of the signal.[2]
Environmental Mitigation Measures
The environmental impact associated with passive seismic techniques are minimal because the source for the survey is naturally occurring. The surface impact from temporary seismometer installations varies and is survey-specific.
Physical Properties

Potential Pitfalls
• Passive seismic techniques cannot provide direct information regarding the temperature or water recharge characteristics of a geothermal system. Passive seismic data can map zones of porosity and permeability and provide a target for futher studies such as heat flow measurements or thermal gradient mapping.[3]

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