Induced seismicity
Induced seismicity ( induced seismicity ) are earthquakes caused by human activities.
It refers to small seismic events (small earthquakes). They arise, for example by mining ( coal mining ), the damming of reservoirs, the injection of water into deep wells, pumping water from a great depth at which geothermal energy, or by hydraulic fracturing ( hydraulic fracturing ) in the production of crude oil or natural gas or by underground explosions. In most cases, the strength of the induced seismic events is very low and is usually below the limit of perceptibility by humans. However, larger earthquakes with magnitudes above 5 are already created.
Sometimes a distinction is " induced seismicity " ( triggered seismicity ) of " induced seismicity ". When triggered seismicity natural stresses are reduced, caused by human intervention to a local stress field. When induced seismicity voltages causes until they degrade through a seismic event.
Induced and Triggered Seismicity can be caused by changes in the mechanical stresses or changes in the shear strength of rock in the Earth's crust that are caused by humans. Loads on the Earth's surface there by the weight of water from reservoirs, relief by mining. Pressed fluids or increased pore water pressure can reduce the shear strength of the rock. The water acts as a lubricant in dislocations or fractures between the stone slabs.
In several dams stausee induced earthquakes have been observed or suspected. The strongest known stausee induced earthquake (magnitude 6.5 ) took place on 10 December 1967, to the Koyna Dam southeast of Bombay in India instead. Here, 200 people came to our life and there was great damage to property. The dam itself did not break, but it was a crack. Other cases are:
- Xinfeng Reservoir ( Hsinfengkiang ), China, Magnitude 6.1 (1962 )
- Kariba Dam
- Lake Mead ( Hoover Dam )
- Nurek Dam
- Kremasta Dam
- Zipingpu Dam ( suspected)
A variety of other cases of induced seismicity in dams is known.
Induced earthquakes by other works were, for example, the following events:
- 1962-1966 is pressed in Denver, Colorado, about 620,000 cubic meters of chemical waste in the underground. During the injections in 1300 seismic events were recorded up to a magnitude of about 5.0. The largest earthquake occurred only after the end of the pressings.
- In the Kaliabbaugebieten in central Germany were produced during collapse of cavities underground earthquake, so at Sünna on 23 June 1975 at Völkershausen on March 13, 1989 in Halle ( Saale) on 11 September 1996.
- The end of 2006 sparked a sample hole of "Deep Heat Mining Basel " project near Basel hundreds of small tremors. Some of which reached a magnitude of 3.5 and damaged buildings.
- Were presented in May 2011 in Lorca, Spain, triggered by groundwater extraction earthquake, which reached a magnitude of 5.1. Here, nine people were killed.