Quantitative imaging of the Permo‐Mesozoic complex and its basement by frequency domain waveform tomography of wide‐aperture seismic data from the Polish Basin     

Michal Malinowski  Stéphane Operto 《Geophysical Prospecting》2008,56(6):805-825

In this study we present the workflow and results of 2D frequency domain waveform tomography applied to the global‐offset seismic data acquired in central Poland along a 50‐km long profile during the GRUNDY 2003 experiment. The waveform tomography method allows full exploitation of the wide‐aperture content of these data and produces in a semi‐automatic way both the detailed P‐wave velocity model and the structural image (i.e., perturbations in respect to the starting model). Thirteen frequencies ranging from 4 to 16 Hz were inverted sequentially, gradually introducing higher wavenumbers and more details into the velocity models. Although the data were characterised by relatively large shot spacings (1.5 km), we obtained clear images both of the Mesozoic and Permian sedimentary cover. Velocity patterns indicated facies changes within the Jurassic and Zechstein strata. A high velocity layer (ca. 5500 m/s) was found near the base of Triassic (Scythian), which made the imaging of a deeper layer difficult. Nevertheless, we were able to delineate the base of the Permian (i.e., base of the Rotliegend), which was not possible to derive from conventional common‐depth‐point processing, as well as some deeper events, attributed to the Carboniferous. The sub‐Permian events formed a syn‐form which favoured our previous interpretation of a depression filled with Upper Carboniferous molasse. The validity of the waveform tomography‐derived model was confirmed by well‐log data. Forward ray‐tracing modelling and synthetic seismograms calculations provided another justification for the key structures present in the waveform tomography model.  相似文献   

Fresnel volumes corresponding to PKP waves in the IASP91 model     

Michal Kvasnička  Jaromír Janský 《Journal of Seismology》1999,3(4):375-391

Fresnel volumes provide a suitable tool for estimating the resolution limits or accuracy of tomographic methods based only on the arrival times of these seismic waves, which penetrate the deep interior of the Earth. The standard definition of the Fresnel volume was modified to include effects of multipathing, i.e., multivalued travel times. Computations were performed in the IASP91 model for three representative epicentral distances and two prevailing signal periods. Preliminary results have been obtained. They place a rather strong restriction on the resolution limits of tomographic methods, depending on the prevailing period, due to the relatively large fatness of PKP Fresnel volumes.  相似文献   

Late quaternary paleogeography of Middle Europe and the Northcentral United States: A framework for comparative studies of prehistoric man-land relationships     

John Bower  Michal Kobusiewicz 《Geoarchaeology》1988,3(2):117-125

The work summarized in this paper is an important component of a larger study concerned with the responses of prehistoric hunting-gathering cultures to long term environmental change. the general approach involves comparing cultural systems and their transformations in Middle Europe and the northcentral United States during the late Pleistocene and early Holocene transition from glacial to interglacial conditions. This paper is specifically aimed at identifying ecological factors that may help account for similarities and differences in the cultural successions on opposite sides of the Atlantic. We conclude that, despite broadly similar environmental histories in both regions, important differences are evident in, for example, trajectories of climatic amelioration. These, together with differences in human demography, can be seen to have contributed toward shaping divergent cultural adaptations in Europe and North America.  相似文献   

Modelling multiseasonal preferential transport of dissolved organic carbon in a shallow forest soil: Equilibrium versus kinetic sorption     

Jaromir Dusek  Michal Dohnal  Tomas Vogel  Anne Marx  Johannes A.C. Barth 《水文研究》2019,33(22):2898-2917

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A modern analogue of the Pleistocene steppe‐tundra ecosystem in southern Siberia     

Milan Chytrý  Michal Horsk  Ji&#x;í Danihelka  Nikolai Ermakov  Dmitry A. German  Michal Hjek  Petra Hjkov  Martin Ko í  Svatava Kube&#x;ov  Pavel Lustyk  Jeffrey C. Nekola  Vra Pavelkov &#x;i nkov  Zdenka Preislerov  Philipp Resl  Milan Valachovi 《Boreas: An International Journal of Quaternary Research》2019,48(1):36-56

Steppe‐tundra is considered to have been a dominant ecosystem across northern Eurasia during the Last Glacial Maximum. As the fossil record is insufficient for understanding the ecology of this vanished ecosystem, modern analogues have been sought, especially in Beringia. However, Beringian ecosystems are probably not the best analogues for more southern variants of the full‐glacial steppe‐tundra because they lack many plant and animal species of temperate steppes found in the full‐glacial fossil record from various areas of Europe and Siberia. We present new data on flora, land snails and mammals and characterize the ecology of a close modern analogue of the full‐glacial steppe‐tundra ecosystem in the southeastern Russian Altai Mountains, southern Siberia. The Altaian steppe‐tundra is a landscape mosaic of different habitat types including steppe, mesic and wet grasslands, shrubby tundra, riparian scrub, and patches of open woodland at moister sites. Habitat distribution, species diversity, primary productivity and nutrient content in plant biomass reflect precipitation patterns across a broader area and the topography‐dependent distribution of soil moisture across smaller landscape sections. Plant and snail species considered as glacial relicts occur in most habitats of the Altaian steppe‐tundra, but snails avoid the driest types of steppe. A diverse community of mammals, including many species typical of the full‐glacial ecosystems, also occurs there. Insights from the Altaian steppe‐tundra suggest that the full‐glacial steppe‐tundra was a heterogeneous mosaic of different habitats depending on landscape‐scale moisture gradients. Primary productivity of this habitat mosaic combined with shallow snow cover that facilitated winter grazing was sufficient to sustain rich communities of large herbivores.  相似文献   

泰国近岸古环境Toarcian-Aalenian期风暴沉积初探     

Assanee MEESOOK  Michal KROBICKI 《地球学报》2012,33(S1):40-40

Jurassic deposits of the Malayan Peninsula (Thailand) are stratigraphically limited to Toarcian and Aalenian only (Meesook & Sha, 2010, and literature cited therein). These are represented by wide spectrum of both clastic and carbonate rocks with full develop-ment of transitional ones. In the middle part of penin-sula (vicinity of Krabi) distribution of Jurassic facies suggest occurrence of full marine palaeoenvironments in NE part of it with gentle transition by lagoonal (brackish?) and tidal environments up to terrestrial ones in the SW part of peninsula. Sections studied, close to Thung Song city, are represented by 20 m thick sequence of thin-bedded limestones and marls of the Khlong Min Formation, most probably lagoonal palaeoenvironments (transitional = restricted ma-rine-brackish), indicated by specific benthic fauna dominated by different kind of ethological group of bivalves – infaunal, epifaunal and encrusted (epibion-tic) species like Protocardia, Praemytilus, Modiolus, Myrene, and Actinostreon. Very characteristic is a lack of full marine, stenohaline, other invertebrates – brachiopods, crinoids, echinoids etc.  相似文献   

Variscan deformation,microstructural zonation and extensional exhumation of the Moravian Cadomian basement     

Michal Lobkowicz  Karel Schulmann  Radek Melka 《Geodinamica Acta》2013,26(2-3):119-137

Abstract

The Cadomian Dyje Batholith, in the foot–wall of the Variscan Moravian nappe pile, has been involved in Variscan ductile deformation. The Cadomian Brunovistulian rocks were obliquely underthrusted during Carboniferous dextral transpression.

Strain intensity is inversely proportional to the distance from the contact of the Variscan thrust front. The microstructures of deformed granodiorites and quartz–diorites show a characteristic zonality marked by relatively high temperature flow in the west (550–580 °C) characterized by dynamic recrystallization of feldspars and grain boundary migration recrystallization of quartz. The size of quartz grains decreases with decreasing strain towards the east. At the easternmost part of the autochthonous Dyje massif, fracturing of feldspar and subgrain rotation recrystallization of quartz predominate. Flow stress estimates calculated from recrystallized quartz grain size show a regional increase of stress intensity from the highly strained margin towards the less deformed core of the Dyje massif. This microstructural zonation is oblique with respect to the major thrust boundary and corresponds roughly to metamorphic isogrades. The microstructural zonation reflects underthrusting of the Brunovistulian domain below the Moldanubian nappe.

The main ductile tectonic event D₁ is followed by a retrogressive brittle–ductile and brittle deformation D₂. D₂ results in the development of shear zones and faults superimposed on the D₁ mylonite fabric. D₂ is related to extension oblique to the D₁ fabric, associated with detachment and the westward movement of the Moravian nappes. © Elsevier, Paris  相似文献   

Model Fusion and Joint Inversion   总被引：1，自引：1，他引：0  

Eldad Haber  Michal Holtzman Gazit 《Surveys in Geophysics》2013,34(5):675-695

Inverse problems are inherently non-unique, and regularization is needed to obtain stable and reasonable solutions. The regularization adds information to the problem and determines which solution, out of the infinitely many, is obtained. In this paper, we review and discuss the case when a priori information exists in the form of either known structure or in the form of another inverse problem for a different property. The challenge is to include such information in the inversion process. To use existing known structure, we review the concept of model fusion, where we build a regularization functional that fuses the inverted model to a known one. The fusion is achieved by four different techniques. Joint inversion of two data sets is achieved by using iterative data fusion. The paper discusses four different methods for joint inversion. We discuss the use of correspondence maps or the petrophysics of the rocks, as well as structure. In particular, we suggest to further stabilize the well-known gradient cross product and suggest a new technique, Joint Total Variation, to solve the problem. The Joint Total Variation is a convex functional for joint inversion and, as such, has favorable optimization properties. We experiment with the techniques on the DC resistivity problem and the borehole tomography and show how model fusion and joint inversion can significantly improve over existing techniques.  相似文献   

Integral transformations of deflections of the vertical onto satellite-to-satellite tracking and gradiometric data     

Michal Šprlák  Pavel Novák 《Journal of Geodesy》2014,88(7):643-657

With the advent of geodetic satellite missions mapping almost globally the Earth’s gravitational field, new methods and theoretical approaches have been developed and investigated to fully exploit the potential of their new observables. Besides estimating values of numerical coefficients in harmonic series of the gravitational potential, new applications emerged such as data validation and combination. In this contribution, new integral transformations are presented which transform principal components of the terrestrial deflection of the vertical onto disturbing satellite-to-satellite tracking and gradiometric data at altitude. Using spherical approximation, necessary integral kernel functions are derived in both spectral and closed forms. The behaviour of isotropic kernel functions is studied and the new integral transformations are tested in a closed-loop simulation using synthetic terrestrial and satellite data synthesized from a global gravitational model. New integral transformations can be used for data validation and combination purposes.  相似文献   

Holocene history and environmental reconstruction of a Hercynian mire and surrounding mountain landscape based on multiple proxies     

Lydie Dudová  Petra Hájková  Věra Opravilová  Michal Hájek 《Quaternary Research》2014

We discovered the first peat section covering the entire Holocene in the Hrubý Jeseník Mountains, representing an island of unique alpine vegetation whose history may display transitional features between the Hercynian and Carpathian regions. We analysed pollen, plant macrofossils (more abundant in bottom layers), testate amoebae (more abundant in upper layers), peat stratigraphy and chemistry. We found that the landscape development indeed differed from other Hercynian mountains located westward. This is represented by Pinus cembra and Larix during the Pleistocene/Holocene transition, the early expansion of spruce around 10,450 cal yr BP, and survival of Larix during the climatic optimum. The early Holocene climatic fluctuations are traced in our profile by species compositions of both the mire and surrounding forests. The mire started to develop as a calcium-rich percolation fen with some species recently considered to be postglacial relicts (Meesia triquetra, Betula nana), shifted into ombrotrophy around 7450 cal yr BP by autogenic succession and changed into a pauperised, nutrient-enriched spruce woodland due to modern forestry activities. We therefore concluded that its recent vegetation is not a product of natural processes. From a methodological viewpoint we demonstrated how using multiple biotic proxies and extensive training sets in transfer functions may overcome taphonomic problems.  相似文献