Study on ground surface fissures in the broader area of the lignite mines of Mavropigi village, Eordaia prefecture, northern Greece

Περίληψη

During the July 2010 a ground fissure was observed in the field, near the village of Mavropigi, in its NW side. Various interpretations about the phenomenon were proposed by the local authorities. At the beginning of September 2010, another ground fissure close and almost parallel to the previous one and very close to the limits of the lignite exploitation by the Public Power Corporation (PPC), appeared. The lignite deposits are found in Neogene sediments, consisting of alternation of clayey and marly layers. The geotectonic survey indicated that the aforementioned fissures moved in a slightly different way, though it was considered that they both operated together based on the same causative. In order to investigate if these tectonic phenomena are results of seismic activity in the region, five digital seismometers installed inside and around the village of Mavropigi. They were in operation for about five months. The obtained results compared with the records received by the national network of seismographs in order to inspect if the shocks are local or not. Afterwards, the ninety local events separated for further processing. Firstly, a map of seismicity with the epicenters of the ninety events produced. A first inspection in the map showed that almost all the events formed a group near the lignite mine which is in Southeast direction of Mavropigi. The seismological investigation revealed that the seismicity of the region characterized as low. There were used two different velocity models for the epicenters’ location, one characterized by high velocities and the second that characterized by low velocities. The second considered to be more accurate because of the lower error values. Using the low velocities model, constructed a map of the epicenters of the recorded seismic events and observed that most of the data form a group within Kardia mine, in the South-East of Mavropigi. Afterwards, an extensive observation in the waveforms of these seismic events found that have explosion characteristics rather than these of earthquakes. It turned out that these seismic events are directly related to the mining activity (e.g. blasts) in the mines of P.P.C., which located in the region, South-East of Mavropigi.