We develop and test a new hybrid approach of the amplitude and waveform moment tensor inversions, which utilizes the principal component analysis of seismograms. The proposed inversion is less sensitive to noise in data, being thus more accurate and more robust than the amplitude inversion. It also suppresses other unmodeled phenomena, like a directivity of the source, errors caused by local site effects at individual stations, and by time shifts in arrivals of observed and synthetic signals due to an inaccurate velocity model. This inversion is computationally less demanding than the full waveform inversion and thus applicable to large sets of earthquakes. The approach is numerically tested on synthetic data with various levels of noise. The applicability of the inversion is demonstrated on inverting more than 800 microearthquakes that occurred during the 2014 activity in West Bohemia, Czech Republic. The analysis revealed several distinct clusters of moment tensors. Focal mechanisms corresponding to moment tensors of three clusters are left-lateral strike slips associated with the most active fault in the focal zone. Another cluster is characterized by right-lateral strike slips associated with the fault conjugate to the main fault. Finally, we identified a cluster with pure reverse focal mechanisms that are anomalous and not expected to occur in the region. These mechanisms were not detected in previous seismic activity, and they have an unfavorable orientation with respect to regional tectonic stress. This might indicate a presence of local stress heterogeneities caused, for example, by an interaction of faults or fault segments in the focal zone.

The aim of the present work was to compare the distribution of selected metals in tissues of several fish species caught in the Věstonice reservoir. The hygienic quality of fish meat was assessed with respect to the mercury concentration. A total of 35 fish of the following species were caught: carp (Cyprinus carpio), bream (Abramis brama), asp (Aspius aspius), pikeperch (Sander lucioperca) and pike (Esox lucius). Samples of muscle, liver (hepatopancreas), kidney, gonads and gills were analyzed. Hg, Pb, Cd, Cu, Zn and Cr concentrations in fish tissues were determined by the AAS. The results showed that different metals differ in their affinity to different fish tissues (e.g. Cu -liver, Cd -kidney). Mercury concentrations along the food chain increase, i.e. higher mercury concentrations are found in predatory fish. Contrary to mercury, cadmium and lead concentrations do not show any increases along the fish part of food chain in surface water ecosystems. In predatory fish, lower concentrations of these metals were found than in nonpredatory fish species. Differences in concentrations between ovaria and testes were found only in Cu and Zn. To evaluate possible health risks of mercury concentrations for consumers, the risk index was calculated and maximum admissible amounts of muscle meat for consumption were determined. The results confirmed good hygienic quality of market-ready fish from the Věstonice reservoir. Predatory fish, non-predatory fish, heavy metals, AAS, risk indexThe rising living standards of human population take their toll in increasing loads to the environment with various contaminating substances that occur naturally at very low concentrations, or do not naturally occur at all. Besides metal manufacturing and processing, the sources of environmental metal contamination include industrial waste products, the burning of fossil fuels, and the use of metals by consumers. The increase in metal concentrations in the environment is further enhanced by their poor degradability resulting in metal accumulation in the soil, water sediments and the food chain (Svobodová et al. 1987).As the final link of the food chain in the aquatic environment, fish are an important indicator of contamination by a number of substances, including metals (Svobodová et al. 1996). Moreover, toxic metal concentrations in fish are monitored also in terms of food safety (Svobodová et al. 2004). First and foremost, the most closely monitored potentially toxic metals include mercury followed by cadmium and lead. In recent years, food safety has been a priority in EU member states. Hence, the large number of regulations targeting veterinary food hygiene that are being adopted mainly by the European Food Safety Authority (EFSA) and other organisations. At present, hygienic limits are determined by the highest acceptable levels of contaminants in foodstuffs in the Commission Regulation 1881/2006/EC as amended and Decrees 68/2005 Sb. and 305/2004 Sb. of the Ministry of Health. As far as fish as food animals are concerned, the m...

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Summary Earthquake swarms represent a special case of seismic activity, featuring seismic energy released gradually by many earthquakes without a dominant event, in a short time period. Behavior like this offers detailed insight into the processes on activated faults. An earthquake swarm enabling such insight hit the West Bohemia/Vogtland earthquake swarm region during May 2018. The swarm contained more than 4000 earthquakes with ML = 〈0.5, 3.8〉 which occurred within two weeks period. During this time the activity character significantly changed: what started as a pure earthquake swarm ended as a typical mainshock-aftershock sequence. Based on precise double-difference relocations, four fault segments differing in strikes and dips were identified with similar dimensions. The activity started by consecutive activation of two fault segments with a typical earthquake swarm character, and ended with activation of a fault segment hosting a mainshock-aftershock sequence two weeks later. The differences were observable in the earthquakes spatio-temporal evolutions (systematic vs. disordered migration of the hypocenters), b-values (>1.3 for the swarm, <1 for the mainshock-aftershocks), or the smoothness of seismic moment spatial distribution along the fault plane. We interpret our findings in terms of the varying roughness of the fault plane that allows for creating large ruptures at some fault segments and only small ones on the others. This could be related to fluids circulating along the fault plane and their interplay with the seismic cycle.

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