Earthquake swarm
As earthquake swarm or swarm quake a particular form of earthquake series is referred to in geophysics. This occurs several earthquakes within a limited period in certain regions of the earth's crust. The tremor usually have a similar strength and its accumulation can last for several days to approximately 1 year.
Characteristic is often a slow temporal arrival and decay of seismic activity that is subject to any known law. Since the magnitude of the earthquake swarm of earthquakes differ only slightly, no classification of seismicity in pre-, main - and aftershocks can be made.
The term earthquake swarm was first used in 1899 by Josef Knett in a treatise on an accumulation of more than 100 macroseismic perceived earthquakes in the region Vogtland / Western Bohemia, which occurred in 1824 within five weeks. In August and September 2011 and before that in October 2008, September-November 2000 and in winter 1985/86 the earth shook again in the Vogtland / Bohemia. On 14 October 2008 was the strongest measured earthquake in this region, which reached a magnitude of 4.4 on the Richter scale. The epicenter of the quake was near the Czech town of Nový Kostel in 8 to 10 miles deep.
Earthquake swarms occur worldwide mainly in volcanically active regions. It is believed, therefore, that they are caused by the movement of fluids in the crust. Even artificial caused swarms of micro- earthquakes have been observed for example in oil production and compression tests in deep boreholes.
In Germany there are earthquake swarms, for example, in the Vogtland and the Hochstaufen at Bad Reichenhall. In the latter area has been shown that there is earthquake swarms after heavy rain.