Reservoirs
The mass of water in a reservoir alters the pressure in the rock below and through fissures in the rocks, lubricates the fault, which can trigger earthquakes. 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. 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. 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. 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. However, researchers have been denied access to seismological and geological data to examine the cause of the quake further.
Some experts worry that the Three Gorges Dam in China may cause an increase in the frequency and intensity of earthquakes.
Read more about this topic: Induced Seismicity, Causes