Unlike traditional seismic technologies, passive seismic methods observes and measures the natural seismic activities which is already occurring underground or which is inducted.
Passive seismic is the observation of very small-scale earthquakes which occur naturally in the ground when energy is released as a result of rock failure along a fault or as a result of human activities.
Natural seismic activity or human inducted activities as mining, hydraulic fracturing, enhanced oil recovery, geothermal re-injection operations or underground gas storage changes the stress distribution or the volume of a rockmass, inducing a re-distribution of the seismic equilibrium with a releasing of energy in micro seismic events form arousing a re-distribuition of the stress within the rockmass which suddenly slip or shear along pre-existing zones of weakness such as along faults or fracture networks.
Traditional micro seismic mapping determines the location and magnitude of the event and when micro seismicity is observed over time, operators may start to see patterns of seismicity related to production activities.
Passive seismic science grew out of earthquake seismology and low frequency spectrometry, it focuses on local micro-earthquakes (i.e. magnitude less than zero) detectable by array of 3D superficial, borehole or fore hole seismometers and on the seismic energy distribution over time.
Explorations for hydrocarbon and geothermal purposes.