Induced seismicity

In seismology, induced seismicity has two meanings: intentional and unintentional. Intentional induced seismicity or reflection seismology is the production of seismic waves by various means for the purpose of gathering subsurface "images" for energy and mineral exploration purposes.

Unintentional 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.

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 filling of the Katse Dam in Lesotho, and the Nurek Dam in Tajikistan is an example. [ [http://www.internationalrivers.org/en/africa/lesotho-water-project International Rivers] ] In Zambia, Kariba Lake may have provoked similar effects. 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. [http://internationalrivers.org/en/node/1477 Reservoir-Induced Seismicity] ]

Some experts worry that the Three Gorges Dam in China may cause earthquakes — and the proximity of the epicenter of the 2008 Sichuan earthquake to the dam suggests a potential correlation. [ [http://www.probeinternational.org/catalog/content_fullstory.php?contentId=6809&cat_id=7 Probe Int'l 5-14-2008] ] Seismic activity was predicted in the area independent of the construction of the dam by recent developments in world seismology. Some geologists believe that the Zipingpu Dam, dangerously damaged by the Sichuan quake, may be implicated in it. Unquestionably, the Zipingpu reservoir stresses the fault that caused the quake. [ [http://www.probeinternational.org/catalog/content_fullstory.php?contentId=6840&cat_id=7 Probe Int'l 6-5-2008] ] . [ [http://www.probeinternational.org/catalog/content_fullstory.php?contentId=6846&cat_id=7 Probe Int'l 6-10-2008] ]

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 [ [http://egsp.lyellcollection.org:/cgi/content/abstract/5/1/405 Redmayne,D.W. 1988. Mining induced seismicity in UK coalfields identified on the BGS National Seismograph Network. Geological Society, London, Engineering Geology Special Publications; v. 5; p. 405-413] ] . 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. [ [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V63-4JHMFNB-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5e4d2f903fb0995f9c0b05c60b84759b] R.M.H.E. Van Eijsa, F.M.M. Muldersa, M. Nepveua, C.J. Kenterb and B.C. Scheffers. 2006. Correlation between hydrocarbon reservoir properties and induced seismicity in the Netherlands. Engineering Geology, 84, 99-111]

References