Several types of engineering developments are suspected, with varying amounts of evidence, of triggering the occurrence on a limited localized scale and referred as induced-seismicity. The strength of induced seismic (IS) activity range from moderately sized, damaging, earthquakes with the range of failure of the order of kilometers, through to rock bursts, and down to micro-seismic emissions, which are mostly sensed by instrumentation and have range of failure on a scale of meters. Historically, the development of large reservoirs for power generation was the first type of engineering activity that significantly affected the earth's crust and seismicity is associated with such stress modifications. The largest event recorded was 6.5 on Richter scale and associated with the impoundment of very large reservoirs. The actual (3) incidence of Reservoir Induced Seismicity (RIS) is associated to about hundred twenty reservoirs of different sizes. Other induced seismic activities are related with mining ( MIS - 5.7 in potash), fluid injection and disposal ( Denver Arsenal 5.2), fluid withdrawal (Strachan, Alberta - 4.3) and geothermal (Goldsmith, TX, 3.5), enhanced oil recovery (3.0) and storage of oil and gas in the underground caverns, mostly associated to microseismic activity generated by the gas pressure variations.
Reservoir Induced Seismicity (RIS) used to be considered as a strange unintentional environmental phenomenon, which was generally detected without instruments. It was observed in relation to new impoundments and presented a problem to the professional and scientific community for many years. Today, RIS is recognized mostly as an environmental and dam safety-related concern, which is largely understood but for which there are limited means of prediction on a consistent basis. The first engineering operation to be aborted on environmental grounds, was associated with seismic activities at a series of deep wells for disposal of contaminated fluids at the Rocky Mountain Arsenal in Denver Colorado USA, in 1966. Not all seismic activity was proved to be connected with the fluid disposal, but awareness and social sensitivity brought the operation to an end because of environmental concern associated to increased social sensitivity rather than real threats. RIS is of particular concern in areas of low natural seismicity, where potential larger induced events might be higher than the natural activity.
Contributions of Dr. Thomas Vladut, Ph.D., P.Eng.
Contributions of Dr. Valentina Baranova, Ph.D., Geotectonics
Contributions of Mr. Azer Mustaqeem, Application Geoscientist