Magnetic field seeding by galactic winds     

Serena Bertone  Corina Vogt  Torsten Enßlin 《Monthly notices of the Royal Astronomical Society》2006,370(1):319-330

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Hypocenter migration of fluid-induced earthquake swarms in the Tjörnes Fracture Zone (North Iceland)     

Martin Hensch  Carsten Riedel  Jrg Reinhardt  Torsten Dahm  The NICE-People 《Tectonophysics》2008,447(1-4):80

The Tjörnes Fracture Zone separates Iceland's North Volcanic Zone from Kolbeinsey-Ridge (Greenland-Sea). Seismicity mainly occurs in swarms, often 100 and more per day, with similar waveforms and frequently offshore.We analysed three earthquake swarms between June and September 2004, recorded by 35 stations, i.e. the permanent Icelandic SIL network and a temporary setup of land and ocean-bottom-seismometers, and 5 swarms of the years 1994-1997 only using the sparser SIL network. Events occurring in the same swarm often show similar waveforms at the same station. We cross-correlated these time series by using a new approach of three component cross-correlation in order to relocate the hypocenters relative within the swarms and to precisely determine the direction and velocity of migration. Our method delivered good relocations with small spatial and temporal errors. This allows the interpretation and characterisation of the observed earthquake swarms. We try to classify observed migration velocities by comparing them to typical fluid- and crack-propagation velocities and determine focal-mechanisms and orientation of the best fitting plane through the hypocenter distribution.We separate the investigated events into two types of earthquake swarms, supposedly dike-induced and hydrothermally- or gas-induced swarms, by pointing out typical characteristics of both types and by comparing them to similar events of other volcanic regions. Based on different migration velocities, we will discuss possible mechanisms and their triggers of all single clusters within a swarm. Hypothetic models will be established, trying to explain the processes during the swarm episodes and to derive possible pre-eruptive patterns from the character of seismicity.  相似文献   

An experimental database for the development,calibration and verification of constitutive models for sand with focus to cyclic loading: part II—tests with strain cycles and combined loading     

Torsten Wichtmann  Theodoros Triantafyllidis 《Acta Geotechnica》2016,11(4):763-774

For numerical studies of geotechnical structures under earthquake loading, aiming to examine a possible failure due to liquefaction, using a sophisticated constitutive model for the soil is indispensable. Such model must adequately describe the material response to a cyclic loading under constant volume (undrained) conditions, amongst others the relaxation of effective stress (pore pressure accumulation) or the effective stress loops repeatedly passed through after a sufficiently large number of cycles (cyclic mobility, stress attractors). The soil behaviour under undrained cyclic loading is manifold, depending on the initial conditions (e.g. density, fabric, effective mean pressure, stress ratio) and the load characteristics (e.g. amplitude of the cycles, application of stress or strain cycles). In order to develop, calibrate and verify a constitutive model with focus to undrained cyclic loading, the data from high-quality laboratory tests comprising a variety of initial conditions and load characteristics are necessary. It is the purpose of these two companion papers to provide such database collected for a fine sand. Part II concentrates on the undrained triaxial tests with strain cycles, where a large range of strain amplitudes has been studied. Furthermore, oedometric and isotropic compression tests as well as drained triaxial tests with un- and reloading cycles are discussed. A combined monotonic and cyclic loading has been also studied in undrained triaxial tests. All test data presented herein will be available from the homepage of the first author. As an example of the examination of an existing constitutive model, the experimental data are compared to element test simulations using hypoplasticity with intergranular strain.  相似文献   

Plant–Arthropod Associations from the Lower Miocene of the Most Basin in Northern Bohemia (Czech Republic): A Preliminary Report     

Jakub PROKOP  Torsten Wappler  Stanislav Knor  Zlatko Kva?ek 《《地质学报》英文版》2010,84(4):903-914

Terrestrial plants and insects currently account for the majority of the Earth's biodiversity, and approximately half of insect species are herbivores. Thus, insects and plants share ancient associations that date back more than 400 Myr. However, investigations of their past interactions are at the preliminary stages in Western Europe. Herein, we present the first results of our study of various feeding damage based on a dataset of nearly 3500 examined plant specimens from the Lower Miocene of the Lagerst?tte Bílina Mine in the Most Basin, Czech Republic. This site provides a unique view of the Neogene freshwater ecosystems. It has long been studied by scientists working in different branches of sedimentology, paleobotany, and paleozoology. The fossils are preserved in three characteristic horizons overlaying the coal seam (Clayey Superseam Horizon, Delta Sandy Horizon, and Lake Clayey Horizon), reflecting paleoenvironmental changes in a short time period of development. The trace fossils are classified as functional feeding groups or “guilds”, without searching for a direct cause or a recent analog host relation. Approximately 23% of specimens of dicotyledonous plant leaves were found to be damaged and associated with some leaf “morphotypes”. Deciduous plant–host taxa, and those with a chartaceous texture typical of riparian habitats, were frequently damaged, such as Populus, recorded with two species Populus zaddachii and Populus populina (57.9% and 31% herbivory levels, respectively), followed by Acer, Alnus, and Carya, averaging almost 30% of damaged leaves/leaflets. There has been evidence of 60 damage types (DT) representing all functional feeding groups recorded at the Bílina Mine, including 12 types of leaf mines and 16 gall-type DT. In total, Lower Miocene of the Lagerst?tte Bílina Mine exhibits a high level of external foliage feeding types (23.7%), and a low level of more specialized DT, such as galls (4.3%) and leaf mines (<1%). A broader comparison based on DT of the main sedimentary environments shows significance supporting different biomes by frequency of damage levels and DT diversities.  相似文献   

Robust methods for the decomposition and interpretation of compound dunes applied to a complex hydromorphological setting     

Leon Scheiber  Oliver Lojek  Axel Götschenberg  Jan Visscher  Torsten Schlurmann 《地球表面变化过程与地形》2021,46(2):478-489

Underwater dunes are a morphological feature that are explored by marine scientists and coastal engineers alike. This study presents new methodologies in order to simplify bedform identification and morphodynamic analyses. Specifically, subaqueous compound dunes are decomposed with a simple yet extensive tracking algorithm, which relies on a repeated evaluation of unfiltered bed elevation profiles according to five predefined length classes. In a second step, morphological trends are assessed in the form of bed migration rates, bed slope asymmetries and net sediment changes, in which all parameters are referred to equidistant sections of the examined fairway stretch. This integrated approach not only avoids the challenges in weighting the varying size and abundance of dunes of different scales but also ensures comparability between dune-specific and areal parameters, which significantly improves the interpretation of the morphological setting as a whole. The developed methods are applied to the Outer Jade fairway, an anthropogenically influenced and regularly maintained waterway in the German Bight, and allow scrutiny of spatio-temporal trends in this region. Based on a unique data set of 100 sequential high-quality echo-sounding surveys, various types of bedforms are identified, comprising large-scale primary as well as superimposing secondary dunes that are assumed to interfere with each other. Temporal trends show a long-term rise of the troughs of major bedforms and constant maximum crest elevations near the official maintenance depth, which matches the observed long-term aggradation of sediments. The spatial distribution of integrated morphodynamic parameters reflects a previously described zone of primary dune convergence and facilitates the precise localization of this geophysical singularity. The presented findings both confirm the robustness of the proposed methodologies and, in return, enhance the understanding of morphological processes in the Outer Jade. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Observing upper troposphere–lower stratosphere climate with radio occultation data from the CHAMP satellite     

Ulrich Foelsche  Michael Borsche  Andrea K. Steiner  Andreas Gobiet  Barbara Pirscher  Gottfried Kirchengast  Jens Wickert  Torsten Schmidt 《Climate Dynamics》2008,31(1):49-65

High quality observations of the atmosphere are particularly required for monitoring global climate change. Radio occultation (RO) data, using Global Navigation Satellite System (GNSS) signals, are well suited for this challenge. The special climate utility of RO data arises from their long-term stability due to their self-calibrated nature. The German research satellite CHAllenging Minisatellite Payload for geoscientific research (CHAMP) continuously records RO profiles since August 2001 providing the first opportunity to create RO based climatologies for a multi-year period of more than 5 years. A period of missing CHAMP data from July 3, 2006 to August 8, 2006 can be bridged with RO data from the GRACE satellite (Gravity Recovery and Climate Experiment). We have built seasonal and zonal mean climatologies of atmospheric (dry) temperature, microwave refractivity, geopotential height and pressure with 10° latitudinal resolution. We show representative results with focus on dry temperatures and compare them with analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Although we have available only about 150 CHAMP profiles per day (compared to millions of data entering the ECMWF analyses) the overall agreement between 8 and 30 km altitude is in general very good with systematic differences <0.5 K in most parts of the domain. Pronounced systematic differences (exceeding 2 K) in the tropical tropopause region and above Antarctica in southern winter can almost entirely be attributed to errors in the ECMWF analyses. Errors resulting from uneven sampling in space and time are a potential error source for single-satellite climatologies. The average CHAMP sampling error for seasonal zonal means is <0.2 K, higher values occur in restricted regions and time intervals which can be clearly identified by the sampling error estimation approach we introduced (which is based on ECMWF analysis fields). The total error of this new type of temperature climatologies is estimated to be <0.5 K below 30 km. The recently launched Taiwan/U.S. FORMOSAT-3/COSMIC constellation of 6 RO satellites started to provide thousands of RO profiles per day, but already now the single-satellite CHAMP RO climatologies improve upon modern operational climatologies in the upper troposphere–lower stratosphere and can act as absolute reference climatologies for validation of more bias-sensitive climate datasets and models.  相似文献   

Book reviews     

Barry Floyd  William J. Torry  Mohamed A. Mohamed Salih  P. P. Karan  Wolf Tietze  Nikolaos Zahariadis  Torsten Malmberg 《GeoJournal》1987,14(1):137-140

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Moment tensors of microearthquakes from the Eyjafjallajökull volcano in South Iceland     

Torsten Dahm  Bryndís Brandsdóttir 《Geophysical Journal International》1997,130(1):183-192

Analyses of relative P - and S -wave amplitudes of 15 selected earthquakes ( M _L <2.3) from a seismic swarm, which occurred in May and June 1994 at the Eyjafjallajökull volcano in South Iceland, reveal similar radiation patterns, a thrust-type double-couple with an additional source component. All focal solutions have nearly vertical T -axes and horizontally oriented P -axes, with E-W-oriented nodal planes. The volume increase corresponding to an isotropic source component is estimated to be in the range of 24 m³. The temporal and spatial seismic pattern, small magnitude range, focal mechanisms and depth range of the Eyjafjallaökull earthquakes indicate vertical intrusion of magma into a confined region at the northern flank of the volcano.  相似文献   

Formation of sequences of cemented layers and hardpans within sulfide-bearing mine tailings (mine district Freiberg,Germany)     

Torsten Graupner  Andrea Kassahun  Dieter Rammlmair  Jeannet A. Meima  Dagmar Kock  Markus Furche  Adrian Fiege  Axel Schippers  Frank Melcher 《Applied Geochemistry》2007

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Variations of the Ca/Ca ratio in seawater during the past 24 million years: evidence from δCa and δO values of Miocene phosphates     

Anne-Désirée Schmitt  Torsten Vennemann 《Geochimica et cosmochimica acta》2003,67(14):2607-2614

The Ca isotope variation of 11 Miocene and Pleistocene, authigenic, marine phosphates is rather small compared to the corresponding variation in δ¹⁸O values. The δ⁴⁴Ca values are not correlated with the δ¹⁸O values and, therefore, they are not temperature controlled. It is likely that the δ⁴⁴Ca values of the phosphorites reflect the variation in the δ⁴⁴Ca values of paleo-seawater but, in contrast to Sr, not the isotopic composition of seawater itself. Furthermore, Ca and Sr isotopic compositions are decoupled with decreasing stratigraphic age of the phosphate peloids with Sr isotopic compositions changing to more radiogenic values while Ca isotopic compositions remain rather stable. All samples have δ⁴⁴Ca values below present-day seawater values, suggesting that phosphate formation discriminates against heavy Ca isotopes.Phosphorites and carbonaceous sediments have a similar Ca isotopic variation during the Miocene. A systematic and more or less constant shift between marine carbonates and phosphates is observed: the phosphate samples are slightly less enriched in ⁴⁰Ca compared to carbonates. This shift has been related to a mineral-dependent kinetic mass fractionation during precipitation from seawater. The rather stable δ⁴⁴Ca value for the 19 to 9 Ma old phosphorites points to a constant δ⁴⁴Ca fractionation of about 1.1 between seawater and phosphorites during the past and suggests steady-state conditions for the Mid-Miocene seawater (sedimentation flux equals erosion flux).  相似文献