Hydrologic response of underground reservoirs to seismic vibrations

The response of the water level in wells to seismic impacts from remote earthquakes and explosions are analyzed. It is shown that in most cases the magnitude of the postseismic change in the water level scales as a square root of the amplitude of the deformation wave. The intensity of persistent changes averages a dynamical deformation of 1-5 cm/mu strain. Noticeable deviations from the mentioned range are possible, depending on the particular structural features of the layer. The possibility of the destruction of poorly permeable barriers, which are formed in the fractures in rocks during precipitation of microparticles, by dynamical pulses is studied in laboratory experiments. It is shown that the fracture's permeability of the rock may considerably increase even in the range of low-amplitude vibrations which are unlikely to cause a failure of the rock or a growth of the existing cracks in response to the passage of a seismic wave. It is established that the effect may progressively accumulate under the prolonged action of seismic impacts. The change in the number of open cracks and the increase in their effective permeability may bring about fluid migration and variations in pore pressure and, consequently, change the whole range of the local mechanical properties of the rock.