Abstract
Tectonic seismicity in Poland is sparse. The biggest event was located near Myślenice in 17th century of magnitude 5.6. On the other hand, the anthropogenic seismicity is one of the highest in Europe related, for example, to underground mining in Upper Silesian Coal Basin (USCB) and Legnica Głogów Copper District (LGCD), open pit mining in “Bełchatów” brown coal mine and reservoir impoundment of Czorsztyn artificial lake. The level of seismic activity in these areas varies from tens to thousands of events per year. Focal mechanism and full moment tensor (MT) decomposition allow for deeper understanding of the seismogenic process leading to tectonic, induced, and triggered seismic events. The non-DC components of moment tensors are considered as an indicator of the induced seismicity. In this work, the MT inversion and decomposition is proved to be a robust tool for unveiling collapse-type events as well as the other induced events in Polish underground mining areas. The robustness and limitations of the presented method is exemplified by synthetic tests and by analyzing weak tectonic earthquakes. The spurious non-DC components of full MT solutions due to the noise and poor focal coverage are discussed. The results of the MT inversions of the human-related and tectonic earthquakes from Poland indicate this method as a useful part of the tectonic and anthropogenic seismicity discrimination workflow.
Highlights
Earthquakes seldom happen in Poland and earthquakes large enough to cause damage are even more rare
In case of good focal sphere coverage the stability of the nodal plane is good for all types of solutions and wasn’t influenced much by noise. These results indicate that the Jarocin 2012 earthquake full moment tensor (MT) solution was not reliable due to poor focal sphere coverage and noise
The main limitation of the Full moment tensors (full MT) inversion with use of the first arrival P-wave displacement amplitude comes from the focal sphere coverage and its sensitivity to noisy data
Summary
Earthquakes seldom happen in Poland and earthquakes large enough to cause damage are even more rare. The Podhale earthquake from 30th November 2004 ML = 4.8 was the biggest earthquake located in Poland since the instrumental measurements started. The last significant tectonic earthquakes in Poland were located in the Tornquist-Teisseyre zone, where seismic activity was reported in the past Guterch 2009), but only the 2007, ML = 2.8 and 2012, ML = 3.8 seismic events located near Jarocin were recorded (Lizurek et al 2013). Map of significant historical earthquakes as well as those recorded instrumentally is shown on Fig. 1. Seismic activity in USCB (Southern Poland) is very high, there are about 3000 events per year recorded by Polish Seismological Network run by Institute of Geophysics, Polish Academy of Sciences.
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