Integrated geophysical and geological methods to investigate the inner and outer structures of the Quaternary Mýtina maar (W-Bohemia,Czech Republic)     

Christina?FlechsigEmail author  Jens?Heinicke  Jan?Mrlina  Horst?K?mpf  Tobias?Nickschick  Alina?Schmidt  Tomá??Bayer  Thomas?Günther  Carsten?Rücker  Elisabeth?Seidel  Michal?Seidl 《International Journal of Earth Sciences》2015,104(8):2087-2105

The Mýtina maar is the first known Quaternary maar in the Bohemian Massif. Based on the results of Mrlina et al. (J Volcanol Geother Res 182:97–112, 2009), a multiparametric geophysical (electrical resistivity tomography, gravimetry, magnetometry, seismics) and geological/petrochemical research study had been carried out. The interpretation of the data has provided new information about the inner structure of the volcanic complex: (1) specification of the depth of post-volcanic sedimentary fill (up to ~100 m) and (2) magnetic and resistivity signs of one (or two) hidden volcanic structures interpreted as intrusions or remains of a scoria cone. The findings at the outer structure of the maar incorporate the (1) evidence of circular fracture zones outside the maar, (2) detection and distribution of volcanic ejecta and tephra-fall deposits at the surface, and (3) indications from electrical resistivity tomography and gravity data in the area between the Mýtina maar and ?elezná h?rka scoria cone, interpreted as a palaeovalley, filled by volcaniclastic rocks, and aligned along the strike line (NW–SE) of the Tachov fault zone. These findings are valuable contributions to extend the knowledge about structure of maar volcanoes in general. Because of ongoing active magmatic processes in the north-east part of the Cheb Basin (ca. 15–30 km north of the investigation area), the Mýtina maar-diatreme volcano and surroundings is a suitable key area for research directed to reconstruction of the palaeovolcanic evolution and assessment of possible future hazard potential in the Bohemian Massif.  相似文献   

CO2 degassing in the Hartoušov mofette area,western Eger Rift,imaged by CO2 mapping and geoelectrical and gravity surveys     

Tobias Nickschick  Horst Kämpf  Christina Flechsig  Jan Mrlina  Jens Heinicke 《International Journal of Earth Sciences》2015,104(8):2107-2129

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Identification and applicability of analogues for a safety case for a HLW repository in evaporites: results from a NEA workshop     

Ulrich Noseck  Jens Wolf  Walter Steininger  Bill Miller 《Swiss Journal of Geoscience》2015,108(1):121-128

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Observations of the Early Morning Boundary-Layer Transition with Small Remotely-Piloted Aircraft   总被引：1，自引：1，他引：0  

Norman Wildmann  Gerrit Anke Rau  Jens Bange 《Boundary-Layer Meteorology》2015,157(3):345-373

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Long-term ocean simulations in FESOM: evaluation and application in studying the impact of Greenland Ice Sheet melting     

Wang  Xuezhu  Wang  Qiang  Sidorenko  Dmitry  Danilov  Sergey  Schr&#;ter  Jens  Jung  Thomas 《Ocean Dynamics》2012,62(10):1471-1486

The Finite Element Sea-ice Ocean Model (FESOM) is formulated on unstructured meshes and offers geometrical flexibility which is difficult to achieve on traditional structured grids. In this work, the performance of FESOM in the North Atlantic and Arctic Ocean on large time scales is evaluated in a hindcast experiment. A water-hosing experiment is also conducted to study the model sensitivity to increased freshwater input from Greenland Ice Sheet (GrIS) melting in a 0.1-Sv discharge rate scenario. The variability of the Atlantic Meridional Overturning Circulation (AMOC) in the hindcast experiment can be explained by the variability of the thermohaline forcing over deep convection sites. The model also reproduces realistic freshwater content variability and sea ice extent in the Arctic Ocean. The anomalous freshwater in the water-hosing experiment leads to significant changes in the ocean circulation and local dynamical sea level (DSL). The most pronounced DSL rise is in the northwest North Atlantic as shown in previous studies, and also in the Arctic Ocean. The released GrIS freshwater mainly remains in the North Atlantic, Arctic Ocean and the west South Atlantic after 120 model years. The pattern of ocean freshening is similar to that of the GrIS water distribution, but changes in ocean circulation also contribute to the ocean salinity change. The changes in Arctic and sub-Arctic sea level modify exchanges between the Arctic Ocean and subpolar seas, and hence the role of the Arctic Ocean in the global climate. Not only the strength of the AMOC, but also the strength of its decadal variability is notably reduced by the anomalous freshwater input. A comparison of FESOM with results from previous studies shows that FESOM can simulate past ocean state and the impact of increased GrIS melting well.

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Balance Between Autotrophic and Heterotrophic Components and Processes in Microbenthic Communities of Sandy Sediments: A Field Study     

Kristina Sundbäck  Per Nilsson  Claes Nilsson  Benno Jönsson 《Estuarine, Coastal and Shelf Science》1996,43(6):689-706

The microscopic community of a microtidal sandy sediment on the Swedish west coast was studiedin situat two depths (0·5 and 4 m) on four occasions (January, April, August and October). Biomass of microalgae, bacteria, ciliates and meiofauna, as well as primary and bacterial productivity, were quantified. Meiofaunal grazing on algae and bacteria was measured simultaneously by radiolabelling intact sediment cores. Autotrophic biomass dominated the microbial community at both depths and on all sampling occasions, accounting for 47–87% of the microbial biomass. Meiofauna contributed 10–47%, while bacteria and ciliates together made up less than 6%. The microflora was dominated by attached (epipsammic) diatoms, but occasional ‘ blooms ’ of motile species occurred. Vital cells of planktonic diatoms contributed to benthic algal biomass in spring. Primary productivity exceeded bacterial productivity in April and August at both depths, while the balance was reversed in October and January. Meiofauna grazed between 2 and 12% of the algal biomass per day, and between 0·3 and 37% of the bacterial biomass. Almost an order of magnitude more algal (17–138 mg C m⁻²) than bacterial (0·1–33 mg C m⁻²) carbon was grazed daily. At the shallow site, primary productivity always exceeded grazing rates on algae, whereas at the deeper site, grazing exceeded primary productivity in October and January. Bacterial productivity exceeded grazing at both depths on all four occasions. Thus, meiofaunal grazing seasonally controlled microalgal, but not bacterial, biomass. These results suggest that, during summer, only a minor fraction (<10%) of the daily microbenthic primary production appears to enter the ‘ small food web ’ through meiofauna. During spring and autumn, however, a much larger fraction (≈30–60%) of primary production may pass through meiofauna. During winter, meiofaunal grazing is a less important link in the shallow zone, but at sublittoral depths, algal productivity may be limiting, and meiofauna depend on other food sources, such as bacteria and detritus.  相似文献   

Finite element simulation of time dependent fracture and fragmentation processes in rock blasting     

P. J. Digby  L. Nilsson  M. Oldenburg 《国际地质力学数值与分析法杂志》1985,9(4):317-329

Two constitutive models for the simulation of fracture and fragmentation processes in rapidly loaded rocks are studied. The models were included in a wave propagation finite element code. The results obtained from the two models were compared by a study of the intensity and extent of fracturing obtained from two different configurations of explosive charge and reflecting surfaces in a plane strain problem. The evolution of the time dependent fracture pattern and fragmentation process is also presented.  相似文献   

General oceanography,an introduction | G. Dietrich,K. Kalle,W. Krauss and G. Siedler, 1980. Wiley,Chichester, U.K., 2nd ed., xxi + 626 pp., £27.00     

Jens Meincke 《Earth》1982,18(2):183-184

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Local stability and estimation of uncertainty for solutions to inverse problems     

Alexey I. Yaremchuk  Maxim I. Yaremchuk  Jens Schröter  Martin Losch 《Ocean Dynamics》2001,52(2):71-78

 We present a method for studying local stability of a solution to an inverse problem and evaluate the uncertainty in determining true values of particular observables. The investigation is done under the assumption that only the Gaussian part of fluctuations about the local minimum of the cost (likelihood) function is essential. Our approach is based on the spectral analysis of the Hessian operator associated with the cost function at its extremal point, and we put forward an effective iterative algorithm suitable for numerical implementation in the case of a computationally large problem. Received: 16 May 2001 / Accepted: 22 October 2001  相似文献   

Crustal structure and local seismicity in Colombia     

Anibal Ojeda  Jens Havskov 《Journal of Seismology》2001,5(4):575-593

Using P-wave travel time data from local seismicity, the crustal structure ofthe central and southern part of Colombia was determined. A very stableand narrow range of possible velocity models for the region was obtainedusing travel time inversion. This range of models was tested with earthquakelocations to select the best velocity model. The 1D velocity modelproposed has five layers over a halfspace, with interfaces at depths of 4,25, 32, 40 and 100 km and P-wave velocities of 4.8, 6.6, 7.0, 8.0, 8.1and 8.2 km/sec, respectively. According to this model the Moho lies at32 km depth on average. For P-waves, the station corrections range from–0.62 to 0.44 sec and for S-wave they range from –1.17 to 0.62 sec.These low variations in station residuals indicate small lateral velocitychanges and therefore the velocity model found should be well suited forearthquake locations and future starting model for 3D tomography studies.Using this new velocity model, the local earthquakes were relocated. Theshallow seismicity, < 30 km, clearly shows the borders betweentectonic plates and also the main fault systems in the region. The deepseismicity, > 80 km, shows two subduction zones in the country: theCauca subduction zone with a strike of N120^°E, dip of 35^°and thickness of 35 km, and the Bucaramanga subduction zone which has,for the northern part, a strike of N103^°E, dip of 27^° andthickness undetermined and, for the southern part, a strike ofN115^°E, dip of 40^° and thickness of 20 km. Based ondifferences of thickness of brittle crust in the subducted slab and spatialdistribution of the seismicity, the Cauca and Bucaramanga subduction zonesseem to represent independent processes. The Cauca subduction seems tobe connected to the process of the Nazca plate being subducted under theNorth Andes Block. In the Bucaramanga subduction zone, the transitionbetween southern and northern parts and changes in geometry of the slabseem to be gradual and there is no evidence of a tear in the slab, howeverthe local seismicity does not allow us to determine which plate or plates arebeing subducted. The Bucaramanga nest appears to be included into thesubducted slab.  相似文献