If the induced seismicity reaches the larger thresholds, operations are shut down immediately. The second type of traffic light system sets only one threshold. If this threshold is reached, the operations are halted. This is also called a "stop light system". Thresholds for the traffic light system vary between and within countries, depending on the area. However, the traffic light system is not able to account for future changes in seismicity. It may take time for changes in human activities to mitigate the seismic activity, and it has been observed that some of the largest induced earthquakes have occurred after stopping fluid injection. Nuclear explosions Nuclear explosions can cause seismic activity, but according to USGS, the resulting seismic activity is less energetic than the original nuclear blast, and generally does not produce large aftershocks. Nuclear explosions may instead release the elastic strain energy that was stored in the rock, strengthening the initial blast shockwave. U.S. National Research Council report A 2013 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. 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. 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. List of induced seismic events Table References Further reading External links The Human-Induced Earthquake Database Map of reservoir-induced earthquakes at International Rivers WEBINAR: Yes, Humans Really Are Causing Earthquakes – IRIS Consortium One-year seismic hazard forecast for the Central and Eastern United States from induced and natural earthquakes – United States Geological Survey, 2016