Induced seismicity

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In seismology induced seismicity refers to typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. Most induced seismicity is of an extremely low magnitude, and in many cases, human activity is merely the trigger for an earthquake that would have occurred naturally in any case.^{[citation needed]}

Causes

There are a number of ways in which induced seismicity has been seen to occur:

Reservoirs

The mass of water in a reservoir alters the pressure in the rock below, 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 Quedd Fodda Dam. Unfortunately, understanding of reservoir induced seismic activity is very limited. However, it has been noted that semisicity appears to occur on dams with heights larger than 100 meters. The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity.^[1] 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.

In 1967 a 6.3 magnitude earthquake occurred in Maharashtra, India with its epicenter, fore and aftershocks all located near or under the Konya Dam reservoir.^[2] 180 people died and 1,500 were left injured. The effects of the earthquake were felt 230 Kilometers 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. With scares of landslide emerging, the dam was drained and consequently seismic activity was almost nonexistent. On August 1, 1975, a large magnitude 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.^[3] In Zambia, Kariba Lake may have provoked similar effects.

Some experts worry that the Three Gorges Dam in China may cause an increase in the frequency and intensity of earthquakes.^[4]

Buildings

The construction of some supertall buildings can produce induced seismicity. There were several small earthquakes in the area surrounding the Taipei 101 tower following its construction.

Mining

Mining leaves voids that can alter the balance of forces in the rock. These voids may collapse producing seismic waves and in some cases reactivate existing faults causing minor earthquakes^[5]. Natural cavern collapse forming sinkholes would produce an essentially identical local seismic event.

Extraction of fossil fuel and groundwater

Subsidence caused by fossil fuel (oil and/or natural gas) and groundwater extraction can generate seismic waves and minor earthquakes.^[6]

External links

http://www.internationalrivers.org/en/node/3972 A map of reservoir-induced earthquakes (RIS).

http://tais.iaspei.net IASPEI's Triggered and induced seismicity working group website.

References

1. ^ http://internationalrivers.org/de/node/1477
2. ^ Reservoir-Induced Seismicity
3. ^ International Rivers
4. ^ Chen, L. & Talwani, P. (1998) Seismicity in China, Pure and Applied Geophysics, 153, 133-149.
5. ^ Redmayne, D.W. (1988) Mining induced seismicity in UK coalfields identified on the BGS National Seismograph Network. Geological Society, London, Engineering Geology Special Publications; vol. 5; pp. 405-413
6. ^ Van Eijsa, R.M.H.E, Muldersa, F.M.M, Nepveua, M, Kenterb, C.J, Scheffers, B.C. (2006) Correlation between hydrocarbon reservoir properties and induced seismicity in the Netherlands, Engineering Geology, 84, 99-111

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