Mining earthquakes in Ruhr District, Germany

An urban area with more than 5 million inhabitants, born by coal, grown with steel, is going to lose its former most important industry in the coming years: Coal mining. Two mines are left in Ruhr District in western Germany: "Prosper Haniel" and "Auguste Victoria".
Mining earthquakes are a known phenomen in Ruhr District. Mainly there shocks are weak and not significant. But in the last weeks, two years before the mines get closed, the earthquakes become more frequent.

On October 30th a quake of Magnitude 2.6 was felt in northern Oberhausen, caused by mining operations in Prosper Haniel. It was the strongest quake in western Germany (North Rhine-Westphalia) in this year, the strongest Prosper Haniel quake for years. It was precursed by three quakes of Magnitude 1.2, 1.5 and 1.6 on October 29th and 28th. No damage was caused, but is has been a clear sign, that the mine is still active. ShakeMap

For about one week, there was no other mining quake detected in Ruhr district. Until November 11th: Within 50 hours, the seismological observatory of Ruhruniversität Bochum registered 10 earthquakes between Magnitude 1.2 and 1.9 in Haltern (Auguste Victoria). So, it was no real surprise what followed on November 15th, 12.35 local time: The second strongest quake in Germany 2014 (behind Darmstadt), the strongest mining quake for three years: Magnitude 3.6. The shocks were felt in parts of Haltern am See, Marl and Dorsten. (see map)

Epicenter

I visited the epicenter area (Suburb Lippramsdorf-Freiheit) today. Minor damage was visible on a wall, only 80 m south of the estimated epicenter. No structural damage was visible, the situation was normal. A local newspaper confirms this damage. Two residents claimed cracks in walls and tiles.

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It was not the first "big" earthquake in Haltern am See. Similar magnitudes occurred in December 2013 and December 2011. Both were felt with moderate intensities of IV - V. Instrumental measurements confirm Intensity V in Haltern Eppendorf, 1,4 km north of the epicenter, on Saturday.  A very soft, sandy soil increases the amplitude of seismic waves and the earthquake becomes more intensive.
And it won't be the last intensive earthquake. Until the end of coal era, the work in depths of 1200 m will continue and trigger tension to the sandstone layers below Haltern. More quakes will occurr, maybe with similar magnitudes, maybe stronger.

On Sunday, a new mining quake of Magnitude 1.9 occurred, this time again in Oberhausen. It is a very active period currently. Not the first this year, but the strongest. During January and February, several quakes of Magnitude 2 were felt in Oberhausen, causing no damage.

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A third area with continuous earthquakes is Hamm in eastern Ruhr District. Although the last mine was closed there years ago, earthquakes go on. This year, the strongest one reached Magnitude 2.1.

The second active mining area in Northern North Rhine-Westphalia, Ibbenbüren, is also plagued by regular minor earthquakes. Although their Magnitude is ususlly low (rarely stronger than M 2.5), damage to houses is clearly visible in parts of Ibbenbüren and Mettingen. Fears are growing that earthquake magnitudes will increase like they did in Haltern, before the mining activity will be stopped.