Podmořská sopečná činnost patří k fascinujícím přírodním jevům, jež pro svou rozmanitost poutají pozornost jak zájemců o živou přírodu, tak těch, které přitahuje spíše geologie a procesy probíhající na naší planetě. V okolí aktivních podmořských sopek se díky soustavnému obohacování vody o nejrůznější minerály a chemické látky udržuje specifické prostředí, které je domovem unikátních ekosystémů a zdrojem cenných údajů mimo jiné pro výzkum vzniku života na Zemi a vývoje jeho rozmanitosti. Vulkanická činnost na dně oceánu představuje přibližně 75 % celosvětové produkce magmatu, což podtrhuje její význam pro vulkanologii, nezanedbatelná jsou i možná společenská rizika těchto vulkánů. Pokud podmořská erupce vyvolá sesuv, může dojít ke vzniku vln tsunami. Přes uvedené významné aspekty zůstává sopečná činnost pod mořem málo probádaným jevem ve srovnání vulkanismem na kontinentech. Příčina je zřejmá - oceánské dno, z něhož sopky vystupují, se ukrývá pod kilometry vodního sloupce, takže jeho topografii známe méně detailně než topografii povrchu Marsu. and Aleš Špičák.
A grant project for the period 2003-2005, supported by the Grant Agency of the Czech Republic, was set up to determine properties of seismic waves and the structure of the uppermost part of the Earth´s crust in the territory of northern Moravia and Silesia. Quarry blasts and mining induced seismic events served as seismic sources. Permanent, temporary and portable seismic stations were used for the monitoring of these seismic events. During the experiments local microearthquakes were also detected and localized. For the complex evaluation of seismic wave features, data of the CELEBRATION 2000 and SUDETES 2003 refraction experiments were incorporated, as well. The velocity-depth dependence of body waves was searched by joint inversions of travel times of Pg/Sg phases. A special feature of the wave trains, generated by quarry blasts, was a pronounced dispersive character of short-period Rayleigh surface waves. These waves enabled us to establish their dispersion curves, on the basis of which the structure of superficial layers was determined down to a depth of several hundreds of meters., Karel Holub, Jaromír Knejzlík, Bohuslav Růžek, Jana Rušajová and Oldřich Novotný., and Obsahuje bibliografii
PATNET, the seismic network of the University of Patras, monitores regularly the seismic activity in the whole western Greece, using for a HYPO location a model, derived as an average representation for this broad area. One of the active regions of the western Greece is the Gulf of Corinth, which central part lies partially on the edge of the PATNET. Due to this and to the fact that the PATNET stations have mostly the vertical component only, the PATNET HYPO location of events in this region are often characterized by large standard errors in epicentres and especially in depths. Using a sequence of small earthquakes that occurred from February to May 2001 close to the city of Aigion, and was recorded by PATNET and as well by local Corinth rift laboratory (CRL) three-component network (CRLNET), we have derived for PATNET station and local model constants whose aplication improves the PATNET HYPO location of events in central part of Gulf of Corinth. These constants represent the main result useful for improvement of the future PATNET location in the given region., Jaromír Janský, Efthimios Sokos, Anna Serpetsidaki and Helene Lyon-Caen., and Obsahuje bibliografické odkazy
Zemětřesení - jeden z nejmocnějších projevů planety Země, který pozorujeme na jejím povrchu, je většinou způsobeno křehkým porušením (praskáním, trháním) horninového masivu podél existujících zlomů v důsledku tektonického napětí v zemské kůře a ve svrchním plášti. Náhlé prasknutí horniny budí rychlé pohyby v ohnisku zemětřesení, které se dále šíří formou seismických vln do celého zemského tělesa. Vysoké tlaky panující v nitru nepřejí vzniku dutin, nýbrž upřednostňují střižný (smykový) skluz podél zlomové plochy. Vystupuje-li zlom na povrch, můžeme střižné posuvy horninových bloků přímo pozorovat (obr. 1). Z fyzikálního hlediska je zemětřesení komplikovaný nelineární proces křehkého porušení materiálu a v určité omezené oblasti (na zlomech v délce od několika metrů až do stovek kilometrů), odehrávající se v poměrně krátkém časovém úseku (od milisekund do desítek sekund). Velikost skluzu mezi sousedními bloky činí od několika milimetrů až po několik metrů. Čím je skluz rychlejší, tím intenzivněji vyzařuje seismické vlny. U některých zemětřesení se však uplatní i nesmyková složka deformace, a právě těm se v článku věnujeme., Jan Šílený, Václav Vavryčuk, Jiří Zahradník., and Obsahuje seznam literatury
The NKCA and KVCA small-aperture (~ 90 m) seismic arrays in western Bohemia represent the second deployment of this type in the Czech Republic. The arrays have a regular triangular geometric configuration with high gain three-component seismographs in each corner of the triangle. This allows very weak local earthquakes to be detected with a high degree of precision and, thereby, substantially enhances the results of the pre-existing local seismic network (WEBNET). This paper reports on the pilot measurement period. It summarises the final configuration of the arrays and compares the derived results. The measured data have been analysed using the DP/EP system developed by NORSAR. This incorporates several array techniques such as beamforming, f-k analysis, and the cross-correlation method. It has been shown that during the study period, the levels of seismic activity recorded by the seismic arrays were up to fifteen times greater than the levels recorded by the pre-existing seismic network., Jaroslav Štrunc and Milan Brož., and Obsahuje bibliografii
The West Bohemia earthquake swarm foci are approximated by a circular seismic source model, which radius is assumed to depend only on magnitude of the event. We consider two different models of average slip (i) a constant slip and (ii) a slip exponentially scaled to the magnitude of the event. Based on these assumptions, we stacked the contributions of individual events into representative final fault slip. We processed in such a way four significant swarms recorded during the last three decades in 1986, 1997, 2000 and 2008. Constant slip model indicates final slip was composed of 2 or 3 principal asperities located on one or two different planes. On the contrary, scaled slip model indicates that one big asperity prevails. It is not possible yet to select the preferred slip model. Analysis of the temporal activity of all swarms generally shows three principal phases: starting phase, main phase and fading phase; the upwards trend of activity spreading was observed (slip animation is presented in www supplement http://www.ig.cas.cz/kolar/StopPhase/Asperity). The maximal possible cumulative slip value may have reached the order of meters., Petr Kolář, Bohuslav Růžek, Alena Boušková and Josef Horálek., and Obsahuje bibliografii
This paper presents the results of the application of wavelet decomposition to processing data from the GGP sites (The Global Geodynamics Project). The GGP is an international project within which the Earth's gravity field changes are recorded with high accuracy at a number of stations worldwide using superconducting gravimeters. Data with a 5-second sampling interval from Wettzell and Bad Homburg were used for the research. The wavelet transform enables the investigation of the temporal changes of the oscillation amplitudes or the decomposition of the time series for the analysis of the required frequencies. The wavelet decomposition was performed using the regular orthogonal symmetric Meyer wavelet. The research concerned data from an earthquake period recorded at various locations and a quiet period when the gravimeters worked without any disturbances. The decomposition was followed by the Fast Fourier Transform for signal frequency components and then by correlation analyses of corresponding frequency components (for periods from 10 to 60 000 seconds) for all sensor combinations, for the quiet and the earthquake periods separately. Frequency components defining long term changes for all sensor combinations, as well as combinations between two sensors at the same site for the quiet days are characterised by high correlation coefficients. For the time of the earthquake, the Wettzell site data proved strong correlation for all frequency components, while the Bad Homburg site data showed an unexpected decrease of correlation for the majority of frequency components. The authors also showed that wavelet decomposition can be a good method of data interpolation, especially from the time of earthquakes. Moreover, it is a very useful tool for filtering the data and removing the noises., Janusz Bogusz, Anna Klos and Wieslaw Kosek., and Obsahuje bibliografii