I have been saying this for years and people looked at me like i was nutts! There are a many of ways in which induced seismicity has been seen to occur. In the past several years, some energy technologies that inject or extract fluid from the Earth, such as oil and gas extraction and geothermal energy development, have been found or suspected to cause seismic events. Some energy technologies also produce wastes that may be managed through disposal or storage by injection deep into the ground. For example, waste water from oil and gas production and carbon dioxide from a variety of industrial processes may be managed through underground injection. Reservoirs[edit] In deep and large reservoirs, the column of water in a reservoir alters in-situ stress state along an existing fault or fracture. In these very large and deep reservoirs the load of the water column can significantly change the stress state on the fault or fracture by increasing the total stress through direct loading, or decreasing the effective stress through the increased pore water pressure. This significant change in stress state can lead to movement along the fault or fracture resulting in an earthquake.[2] Reservoir-induced seismic events can be relatively large compared to other forms of induced seismicity. The first case of reservoir induced seismicity occurred in 1932 in Algeria’s Oued Fodda Dam. Though understanding of reservoir induced seismic activity is very limited, it has been noted that seismicity appears to occur on dams with heights larger than 100 meters (330 ft). The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity.[3] Induced seismicity is usually overlooked due to cost cutting during the geological surveys of the locations for proposed dams. Once the reservoirs are filled, induced seismicity could occur immediately or with a small time lag. The 6.3 magnitude 1967 Koynanagar Earthquake occurred in Maharashtra, India with its epicenter, fore- and aftershocks all located near or under the Koyna Dam reservoir.[4] 180 people died and 1,500 were left injured. The effects of the earthquake were felt 230 km (140 mi) away in Bombay with tremors and power outages. During the beginnings of the Vajont Dam in Italy, there were seismic shocks recorded during its initial fill. After a landslide almost filled the reservoir in 1963, causing a massive flooding and around 2,000 deaths, it was drained and consequently seismic activity was almost non-existent. On August 1, 1975, a magnitude 6.1 earthquake at Oroville, California, was attributed to seismicity from a massive earth-fill dam and reservoir recently constructed and filled there. The filling of the Katse Dam in Lesotho, and the Nurek Dam in Tajikistan is an example.[5] In Zambia, Kariba Lake may have provoked similar effects. The 2008 Sichuan earthquake, which caused approximately 68,000 deaths, is another possible example. An article in Science suggested that the construction and filling of the Zipingpu Dam may have triggered the earthquake.[6][7][8] Some experts worry that the Three Gorges Dam in China may cause an increase in the frequency and intensity of earthquakes.[9] Mining[edit] Mining leaves voids that generally alter the balance of forces in the rock, many times causing rock bursts. These voids may collapse producing seismic waves and in some cases reactivate existing faults causing minor earthquakes.[10] Natural cavern collapse forming sinkholes would produce an essentially identical local seismic event. Extraction of fossil fuels and disposal of waste[edit] Fossil fuel extraction can generate earthquakes.[11][12] Some oil and natural gas wells produce large amounts of waste water. This high-saline water is usually pumped into salt water disposal (SWD) wells. The weight and lubricity of this waste water has been shown to trigger earthquakes.[13][14] The 2011 Oklahoma earthquake, of magnitude 5.6[15] (often reported as 5.7), which occurred after 20 years of injecting waste water into porous deep formations, is believed by some researchers to be the strongest earthquake induced by injection of material.[16] However, the Oklahoma Geological Survey believes that the quake was most likely due to natural causes, and was not triggered by waste injection.[17] Groundwater extraction[edit] The changes in crustal stress patterns caused by the large scale extraction of groundwater has been shown to trigger earthquakes, as in the case of the 2011 Lorca earthquake.[18] Geothermal energy[edit] Enhanced geothermal systems (EGS), a new type of geothermal power technologies that do not require natural convective hydrothermal resources, are known to be associated with induced seismicity. EGS involves pumping fluids at pressure to enhance or create permeability through the use of hydraulic fracturing techniques. Hot dry rock (HDR) EGS actively creates geothermal resources through hydraulic stimulation. Depending on the rock properties, and on injection pressures and fluid volume, the reservoir rock may respond with tensile failure, as is common in the oil and gas industry, or with shear failure of the rocks existing joint set, as is thought to be the main mechanism of reservoir growth in EGS efforts.[19] HDR and EGS systems are currently being developed and tested in Soultz-sous-Forêts (France), Desert Peak and the Geysers (U.S.), Landau (Germany),and Paralana and Cooper Basin (Australia). Induced seismicity events at the Geysers geothermal field in California has been strongly correlated with injection data.[20] The test site at Basel, Switzerland, has been shut down due to induced seismic events. Largest Events at EGS Sites Worldwide[21] Site Maximum Magnitude Cerro Prieto, Baja California, Mexico[22] 6.6 The Geysers, United States 4.6 Cooper Basin, Australia 3.7 Basel, Switzerland 3.4 Rosemanowes Quarry, United Kingdom 3.1 Soultz-sous-Forêts, France 2.9 Researchers at MIT believe that seismicity associated with hydraulic stimulation can be mitigated and controlled through predictive siting and other techniques. With appropriate management, the number and magnitude of induced seismic events can be decreased, significantly reducing the probability of a damaging seismic event.[23] Induced seismicity in Basel led to suspension of its HDR project. A seismic hazard evaluation was then conducted, which resulted in the cancellation of the project in December 2009. U.S. National Research Council Report[edit] A 2012 report from the U.S. National Research Council examined the potential for energy technologies—including shale gas recovery, carbon capture and storage, geothermal energy production, and conventional oil and gas development—to cause earthquakes.[24] The report found that only a very small fraction of injection and extraction activities among the hundreds of thousands of energy development sites in the United States have induced seismicity at levels noticeable to the public. However, although scientists understand the general mechanisms that induce seismic events, they are unable to accurately predict the magnitude or occurrence of these earthquakes due to insufficient information about the natural rock systems and a lack of validated predictive models at specific energy development sites.[25] The report noted that hydraulic fracturing has a low risk for inducing earthquakes that can be felt by people, but underground injection of wastewater produced by hydraulic fracturing and other energy technologies has a higher risk of causing such earthquakes. In addition, carbon capture and storage—a technology for storing excess carbon dioxide underground—may have the potential for inducing seismic events, because significant volumes of fluids are injected underground over long periods of time.[25]
Posted on: Sun, 16 Feb 2014 04:51:50 +0000
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