More than 1000 years salt has been mined in the environment of the city of Lüeburg. In 956AD king Otto I gave the citizens of the city the right to do so. Following the salt, wealth and prestige came to the place as well as subsurface movements that are still threats to the population even after salt mining has largely been stopped and despite the salt dome being one of the smallest of northern Germany (Pries, 2002).
When you walk through the old city you will immediately realize the dopped levels at the Salzstrasse, which were probably caused by an interplay of climatic conditions and century old mining in the salines. From the old market place to the Strasse am Alten Meere a drop of many meters is obevious. However, the latest movements have all been focussed around the cemetery Michaelisfriedhof. We investigated the area because a citizen had recognized a 90 cm deep crack in her garden. Movements of this size should be concurrent with seismic deformation, so we planted a seismic network around the cemetery in a funeral place and two local schools testing the Hamburg University apparatus controlled by the GEOMESS software to record the activity of fracturing induced by the salt dome.
Unfortunately the testing of the instruments could not be finished during the experiment. Still we find some consistency in the data. We can argue from intercomparisons of the data that the uppermost S-wave velocity is around 800 m/s and from amplitude considerations that possible sources for earthquakes are the eastern edge of the Kalkberg and the deforming space on the cemetery. However, the Kalkberg shows more events than the cemetery and events in total are rare. Seismicity is episodical and seems oscillating between the 2 source regions, so that movement of the salt dome as a whole seems to be a more probable origin for the recorded seismicity than a a fracture on the cemetery.
Figure 5: A registered event from 23/05/05, 21:54h GMT.
1. LUNANET, ein temporäres seismisches Netzwerk zur Messung von deformationsbegleitenden seismischen Ereignissen durch Salztektonik