Induced seismicity

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The term induced seismicity covers earthquakes caused by human activities . This is understood to mean predominantly small seismic events, i.e. hardly or imperceptible earthquakes which are only registered by seismic observatories (see →  Seismograph ). Only in rare cases are there noticeable or even very destructive earthquakes.

causes

Induced seismicity occurs as a result of various human interventions in nature, mostly those that change the local stress conditions in the upper crust or that locally reduce the shear strength of the rock structure in the subsurface. This includes

In the vast majority of cases, the strength of the seismic events caused is very low and is usually below the limit of human perception. But larger earthquakes with magnitudes over 5 have already been registered. The Human-Induced Earthquake Database currently (as of February 2018) lists over 750 earthquakes that are attributable to human activities, most of them (37%) as a result of mining.

Sometimes a distinction is made between “triggered seismicity” and induced seismicity in the narrower sense. When seismicity is triggered, naturally occurring tensions in the upper crust of the earth are reduced by human intervention. In the case of induced seismicity in the narrower sense, tensions in the upper crust of the earth are brought about by human intervention until they are reduced by a seismic event.

Induced seismicity (in a broader sense) can arise from changes in mechanical stresses or changes in shear strength in the rocks of the earth's crust, which are caused by humans. The earth's surface is burdened by the weight of the water in reservoirs , and relief by mining . Injected liquids or increased pore water pressure can reduce the shear strength of the rock. The water acts like a lubricant in faults or fractures in the rock.

In several dams , earthquakes induced by reservoirs have been observed or are suspected. The strongest earthquake, probably caused by reservoirs (magnitude 7.9), took place on May 12, 2008 near the Zipingpu Dam in southern China. 90,000 people were killed and there was major property damage. The dam did not break, but it was cracked. Other cases are:

A large number of other cases of induced seismicity in dams are known.

Earthquakes induced by other construction work were, for example, the following events:

  • From 1962 to 1966 , approximately 620,000 cubic meters of chemical wastewater was injected underground near Denver , Colorado . 1300 seismic events, three of them with a magnitude of at least 5.0, were recorded during operation and also after the injection system was shut down. These strongest earthquakes did not occur until around a year after the grouting had ended.
  • In the potash mining areas in central Germany, earthquakes were generated when cavities collapsed underground, for example at Sünna on June 23, 1975, at Völkershausen on March 13, 1989 and near Halle (Saale) on September 11, 1996.
  • End of 2006, in a 5000 m deep test well of the " Deep Heat Mining Basel " - geothermal project near Basel in a dry rock Hot measure subject triggered deliberately earthquake swarms with hundreds of smaller earthquakes. The strongest of these, however, reached an unexpectedly high magnitude of 3.4 and was thus on the order of magnitude in which buildings can be slightly damaged. This clearly noticeable tremor unsettled politicians and the population so permanently that the project was stopped.
  • In May 2011, earthquakes with a magnitude of 5.1 were triggered in Lorca , Spain, when the groundwater was extracted. Nine people were killed.

swell

  1. ↑ http://www.geophys.uni-stuttgart.de/agis/ Working Group Induced Seismicity
  2. ↑ Induced seismicity ( Memento from August 5, 2013 in the Internet Archive )
  3. ↑ Induced seismicity - vibrations of non-natural origin ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / 129.13.109.100
  4. ↑ a b Science Lexicon online
  5. ↑ Ge Shemin, Liu Mian, Lu Ning, Jonathan W. Godt, Luo Gang: Did the Zipingpu Reservoir trigger the 2008 Wenchuan earthquake? Geophysical Research Letters. Vol. 36, No. 20, 2009, doi: 10.1029 / 2009GL040349 (Open Access)
  6. ↑ CISRG Database: Reservoir Induced Seismicity (up to 1990) after Guha and Patil, 1992
  7. ^ JH Healy, WW Rubey, DT Griggs, CB Raleigh: The Denver Earthquakes. Science. Vol. 161, No. 3848, 1968, pp. 1301–1310, doi: 10.1126 / science.161.3848.1301 (alternative full text access : USGS and Stanford University ; PDF around 2.5 MB each)
  8. ↑ The Deep Heat Mining project in Basel on the website of the Swiss Seismological Service (SED)
  9. ↑ Water extraction was to blame for earthquakes in Spain ( Memento from December 28, 2015 in the Internet Archive )

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