Wednesday 20 March 2013

Polish miners rescued after Earthquake.

On Tuesday 19 March 2013, slightly before 9.10 pm GMT (slightly before 10.10 pm local time) the Lower Silesia Region of southwest Poland was struck by a magnitude 4.7 Earthquake at a depth of 3.7 km, close to the town of Lubin, which was felt as far away as Wroclaw 75 km to the southeast. This did not lead to any problems at the surface, but caused a tunnel collapse at the Rudna Copper Mine 10 km northeast of Lubin, trapping 19 miners underground. All the miners were rescued with only miner injuries after an eight hour operation.

The location of the 19 March Earthquake. Google Maps.

The Rudna Mine is the deepest mine in Europe, with the deepest working shafts 1150 m beneath the surface. It produces an average 231 000 tonnes of copper and 546 tonnes of silver per year, making it the world's top silver producer. The ores are mined from the from the Rotliegendes Sandstone and the shales and dolomites of the Lower Zechstein. The Zechstein was an ancient inland sea in northern Europe, that evaporated away during the Middle to Late Permian, leaving vast mineral deposits that are excavated as far away as northern England. Sea water contains small amounts of copper and silver in ionic form, which precipitate out as salts when seas become trapped and evaporate (as is happening with the modern Dead Sea). Because different ions have different properties they are precipitated out in a sequence as seawater evaporates, which does not show on a small scale, but which can produce distinct, workable, layered deposits when a body as large as the Zechstein evaporates.

The extent of Zechstein deposits beneath northern Europe. GarcĂ­a-Veigas et al. (2011).

Poland is in northern Europe, an area not noted for its Earthquakes, but not completely immune either. Like other areas where Earthquakes are uncommon, it is seldom possible to give a precise cause for Polish Earthquakes, with both probably being the result of more than one source of tectonic pressure. The strongest source of tectonic stress in southern Poland is the impact of Africa with Europe, far to the south. This is causing uplift and folding in the Alpine region of Central Europe, and exert pressure on the rocks further to the north. There are also areas of minor tectonic spreading beneath the Rhine Valley and North Sea, both of which cause stress over a wide area. Finally there is glacial rebound; until about 10 000 years ago much of northern and upland Europe was covered by a thick layer of glacial ice, pushing the rocks of the lithosphere down into the underlying mantle. This ice is now gone, and the rocks are slowly springing back into place, causing occasional Earthquakes in the process.

Archive image from the Rudna Mine. Reuters.

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