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Prague, Czech Republic

Cermakova H.,Academy of Sciences of the Czech Republic | Cermakova H.,Institute of Geophysics CAS | Horalek J.,Academy of Sciences of the Czech Republic
Journal of Seismology | Year: 2015

This paper presents the basic characteristics of the 2011 West Bohemia/Vogtland earthquake swarm and compares it with the swarms in 2000 and 2008. All these swarms occurred in the Nový Kostel focal zone. Up to 25,000 ML≤3.7 events with depths between 6 and 10 km were detected in the 2011 swarm. Utilizing WEBNET data, we analysed the cumulative seismic moment, magnitude-frequency and interevent time distributions, space-time distribution of foci and typical focal mechanisms. For this purpose, we improved the formula for estimating the local magnitude ML used by WEBNET. The 2011 swarm exhibited much higher rapidity than the swarms of 2000 and 2008. The magnitude-frequency distributions of all the three swarms are similar, having the b-value close to 1.0. However, the events of higher magnitudes, roughly ML∼3.0+, depart markedly from the general trend of the weaker events. The probability density functions of the interevent times of all the swarms comply with power law ∝T−1.4, which points to Omori law-like mainshock-aftershock activity. All swarms exhibit a pronounced focal migration; however, no regularity was found. The spatial distribution of the 2011 foci indicates two active fault segments which differ from the segment triggered in the swarms of 2000 and 2008. Furthermore, we analysed the spatial distribution of the mini-swarm of 2013 and found that it complements the swarm of 2011. The prevailing focal mechanisms in the 2011 swarm are of both oblique-normal and oblique-thrust types and correspond closely to the geometry of the activated fault segments. Our analyses indicate that the Nový Kostel area is more complex than was believed to be. © 2015, Springer Science+Business Media Dordrecht. Source

Babuska V.,Institute of Geophysics CAS | Ruzek B.,Institute of Geophysics CAS | Dolejs D.,Charles University | Dolejs D.,Albert Ludwigs University of Freiburg
Tectonophysics | Year: 2015

We propose a new model of the origin of earthquake swarms in West Bohemia/Vogtland (central Europe) by extensive CO2 degassing of carbonates in the metasomatized junction of three mantle domains. The associated volume change of the decarbonation reaction accounts for the continuing subsidence of the Cheb Basin adjacent to the major focal zone. The local stress perturbation created by the subsidence, in combination with the regional stress field, may account for the recurring swarm seismicity. The largest earthquake energy has been continuously released along a steep contact between orthogneisses of the uplifting Krušné Hory/Erzgebirge domain and granites of the subsiding Smrčiny/Fichtelgebirge domain, forming boundary between two lithospheric segments. The physical parameters of both lithologies, Poisson's ratio and bulk modulus, derived from the P- and S-wave velocities at different depths indicate that this high-friction suture might be able to accumulate deformation energy that is being released as periodically recurring seismic swarms. The proposed model represents an alternative to prevailing considerations suggesting that the earthquake swarms were triggered by pressurized fluids of mantle origin, whose sources are however separated from the earthquake foci. © 2015 Elsevier B.V. Source

Grison H.,Institute of Geophysics CAS | Petrovsky E.,Institute of Geophysics CAS | Kapicka A.,Institute of Geophysics CAS | Stejskalova S.,Institute of Geophysics CAS
Catena | Year: 2016

In the case of andic soils - developed on volcanic rocks - permanently humid conditions are essential for andosolisation processes. Although volcanic rocks are usually rich in highly magnetic iron oxides, knowledge about these minerals in andic soils with respect to the soil development is missing. The aim of this contribution is to investigate the relationship between magnetic and basic chemical properties of soils developed on volcanic basement and parameters related to the pedogenesis factors. The studied sites are located on basaltic lava flows in the eastern part of the French Massif Central. Investigated pedons with alu-andic, sil-andic, and vitric properties were pedologically described and analysed by a set of magnetic and soil-chemical methods. Magnetic parameters include low-field volume-specific and mass-specific magnetic susceptibility, frequency-dependent magnetic susceptibility, remanent properties (including S-ratio) and coercivities. Chemical parameters included the pHH2O, soil organic matter, total cation exchange capacity, base saturation, and content of Fe and Al extracted in dithionite-citrate, acid-ammonium oxalate, and pyrophosphate solutions. Micro-morphology of Andosols and parent material was observed by scanning electron microscopy, completed with energy dispersive spectrometry. The pedogenesis factors are represented by parent-rock age, annual precipitation, and soil thickness. Our findings suggest that (1) precipitation is the most important pedogenesis factor with a strong relationship to the relative magnetic grain-size, concentration of ferrimagnetic minerals, aluminium dissolved in pyrophosphate and acid-ammonium oxalate, and content of organic matter; (2) parent-material age shows a well-pronounced relationship with magnetic grain-size parameters represented by the frequency-dependent susceptibility and ratio of saturation remanent to saturation induced magnetisation (Mrs/Ms), selective dissolution parameters, and pHH2O; (3) thickness of soil profile shows a link to Mrs/Ms, pHH2O, and content of organic matter. © 2015 Elsevier B.V. Source

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