Mining-Induced Seismicity in the Saarland, Germany     

Ralf Fritschen 《Pure and Applied Geophysics》2010,167(1-2):77-89

Coal mining in the Saar mine, Germany, is accompanied by mining-induced seismic events. Strong events occur only in certain areas of the mine, other areas exhibit almost no seismicity. Shear events occur simultaneously to non-shear events. The shear events occur in different depths but their epicenters do concentrate in bands. The strike of the bands coincides with the strike of larger regional faults in the area. The seismic events of the Saar mine show some characteristics which distinguish them from seismic events observed in other German coalfields. The Gutenberg–Richter relation, for example, does not hold for these events. Furthermore, radiated seismic energy and extracted coal volume are not correlated. In the Primsmulde field a strong seismic event was observed even before mining in that region started. The event was triggered just by driving roadways into the field. The shear events cannot be explained by the mining process alone. They are presumably induced in certain regions (bands) under tectonic load by an interaction of mining-induced and tectonic stresses. In February 2008, extraction in the Primsmulde field induced a seismic event of magnitude 4, which led to surface vibrations reaching 93 mm/s. After this event, the Primsmulde field had to be abandoned. Future extraction of the Saar mine will be restricted to some small areas not intersected by the event bands found in the Dilsburg Ost and Primsmulde fields. The Saar mine will close in 2011.  相似文献   

Tracking the lithium isotopic evolution of the mantle using carbonatites     

Ralf Halama  William F. McDonough  Roberta L. Rudnick  Keith Bell 《Earth and Planetary Science Letters》2008,265(3-4):726-742

Carbonatites are mantle-derived, intraplate magmas that provide a means of documenting isotopic variations of the Earth's mantle through time. To investigate the secular Li isotopic evolution of the mantle and to test whether Li isotopes document systematic recycling of material processed at or near the Earth's surface into the mantle, we analyzed the Li isotopic compositions of carbonatites and spatially associated mafic silicate rocks. The Li isotopic compositions of Archean (2.7 Ga) to Recent carbonatites (δ⁷Li = 4.1 ± 1.3 (n = 23, 1σ)) overlap the range typical for modern mantle-derived rocks, and do not change with time, despite ongoing crustal recycling. Thus, the average Li isotopic composition of recycled crustal components has not deviated greatly from the mantle value (~ + 4) and/or Li diffusion is sufficiently fast to attenuate significant heterogeneities over timescales of 10⁸ years. Modeling of Li diffusion at mantle temperatures suggests that limited δ⁷Li variation in the mantle through time reflects the more effective homogenization of Li in the mantle compared to radiogenic isotope systems. The real (but limited) variations in δ⁷Li that exist in modern mantle-derived magmas as well as carbonatites studied here may reflect isotopic fractionation associated with shallow-level processes, such as crustal assimilation and diffusive isotopic fractionation in magmatic systems, with some of the scatter possibly related to low-temperature alteration.  相似文献   

Rapid injection of particles and gas into non-fluidized granular material, and some volcanological implications   总被引：3，自引：3，他引：0  

Pierre-Simon Ross  James D. L. White  Bernd Zimanowski  Ralf Büttner 《Bulletin of Volcanology》2008,70(10):1151-1168

In diatremes and other volcanic vents, steep bodies of volcaniclastic material having differing properties (particle size distribution, proportion of lithic fragments, etc.) from those of the surrounding vent-filling volcaniclastic material are often found. It has been proposed that cylindrical or cone-shaped bodies result from the passage of “debris jets” generated after phreatomagmatic explosions or other discrete subterranean bursts. To learn more about such phenomena, we model experimentally the injection of gas-particulate dispersions through other particles. Analogue materials (glass beads or sand) and a finite amount of compressed air are used in the laboratory. The gas is made available by rapidly opening a valve—therefore the injection of gas and coloured particles into a granular host is a brief (<1 s), discrete event, comparable to what occurs in nature following subterranean explosions. The injection assumes a bubble shape while expanding and propagating upwards. In reaction, the upper part of the clastic host moves upward and outward above the ‘bubble’, forming a ‘dome’. The doming effect is much more pronounced for shallow injection depths (thin hosts), with dome angles reaching more than 45°. Significant surface doming is also observed for some full-scale subterranean blasts (e.g. buried nuclear explosions), so it is not an artefact of our setup. What happens next in the experiments depends on the depth of injection and the nature of the host material. With shallow injection into a permeable host (glass beads), the compressed air in the “bubble’ is able to diffuse rapidly through the roof. Meanwhile the coloured beads sediment into the transient cavity, which is also closing laterally because of inward-directed granular flow of the host. Depending on the initial gas pressure in the reservoir, the two-phase flow can “erupt” or not; non-erupting injections produce cylindrical bodies of coloured beads whereas erupting runs produce flaring upward or conical deposits. Changing the particle size of the host glass beads does not have a large effect under the size range investigated (100–200 to 300–400 μm). Doubling the host thickness (injection depth) requires a doubling of the initial gas pressure to produce similar phenomena. Such injections—whether erupting or wholly subterranean—provide a compelling explanation for the origin and characteristics of multiple cross-cutting bodies that have been documented for diatreme and other vent deposits.  相似文献   

Numerical simulation of the thermal maturation, oil generation and migration in the Songliao Basin, Northeastern China   总被引：5，自引：0，他引：5  

Yongsheng Zhou  Ralf Littke   《Marine and Petroleum Geology》1999,16(8):244

The discovery of the giant Daqing oil field in the Songliao Basin led to the realisation of the significant petroleum potential of non-marine basins. In order to reconstruct the basin evolution and oil formation, an integrated organic geochemical-basin modelling study along a regional transect across the Songliao Basin was conducted. It provided a regional heat flow evolution model, and revealed post-orogenic or late syn-orogenic maturation in the Central Depression and pre-orogenic maturation in the Southeast Uplift Zone. Kinetic parameters of petroleum generation for the lacustrine source formations are the basis for the simulation of oil generation and migration in the Songliao Basin. Using the principle activation energy peaking at 54 kcal/mol and a pre-exponential factor of about 4.2·10²⁷ Ma⁻¹, the simulation obtained a relatively good match with the measured transformation ratios. The Qingshankou Formation in the West and East Central Depressions constituted the major source in the basin. Major oil generation, migration and accumulation occurred during the Early Tertiary. In the West Central Depression, the generated oils migrated upwards into the Yaojia Formation followed by the updip migration into the Daqing Anticline and towards the local structural high along the West Slope. In contrast, the oil migration in the East Central Depression was dominated by the downward movement from the lower member of the Qingshankou Formation followed by the updip migration towards the Caoyang Anticline. The simulated oil accumulations are in good agreement with discovered oil fields, implying a potential application of the model for prediction and evaluation of new exploration targets in the basin.  相似文献   

Role of climate changes for wind gap formation in a young,actively growing mountain range          下载免费PDF全文

Andrea Hampel  Ralf Hetzel 《地学学报》2016,28(6):441-448

Wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision. Although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift, the role of climate changes in their formation has never been explored. Here, we use a coupled tectonics–landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation. In models with a constant precipitation rate, rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late, if at all. If precipitation varies, wind gaps form mostly c. 100–200 ka after a transition to drier conditions because of sediment aggradation upstream of the range. Our results suggest that the Pliocene–Quaternary aridification of Central Asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern Tibet.  相似文献   

The Epochs of Early-Type Galaxy Formation     

Daniel Thomas  Claudia Maraston  Ralf Bender 《Astrophysics and Space Science》2002,281(1-2):371-374

By means of population synthesis models with variable α/Fe ratios we derive average ages, metallicities, and [α/Fe] element enhancements for a sample of 126 field and cluster early-type galaxies. We find a clear positive relation between [α/Fe] and velocity dispersion. Zero-point, slope, and scatter of this correlation are the same for cluster and field galaxies. In particular, the [α/Fe] ratios and mean ages of cluster ellipticals are positively correlated. This strongly reinforces the view that the [α/Fe] element enhancement in ellipticals is produced by star formation timescales rather than by variations of the initial mass function. These results indicate that the more massive the galaxy, the shorter is its star formation timescale, and the higher is the redshift of the bulk of star formation. This finding is not compatible with the predictions from models of hierarchical galaxy formation. The lenticular and field galaxies of the investigated sample do not follow the correlation between age and [α/Fe], but contain a non-negligible fraction of galaxies with young average ages and high [α/Fe] ratios. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

The Decay of Supersonic and Super-Alfvénic Turbulence in Star-Forming Clouds     

Mordecai-Mark Mac Low  Michael D. Smith  Ralf S. Klessen  Andreas Burkert 《Astrophysics and Space Science》1998,261(1-4):195-196

Supersonic and super-Alfvénic turbulent motions generate an intricate pattern of shock waves through which the turbulence decays. We here illustrate the spatial structure during shock formation and decay. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system   总被引：2，自引：2，他引：0  

Reinhard Calov  Andrey Ganopolski  Martin Claussen  Vladimir Petoukhov  Ralf Greve 《Climate Dynamics》2005,24(6):545-561

We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO₂ forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.

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Reinhard CalovEmail:

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Late- and post-Variscan cooling and exhumation history of the northern Rhenish massif and the southern Ruhr Basin: new constraints from fission-track analysis     

Harald Karg  Andrew Carter  Manfred R. Brix  Ralf Littke 《International Journal of Earth Sciences》2005,94(2):180-192

Apatite fission-track analyses were carried out on outcrop and core samples from the Rhenish massif and the Carboniferous Ruhr Basin/Germany in order to study the late- and post-Variscan thermal and exhumation history. Apatite fission-track ages range from 291±15 Ma (lower Permian) to 136±7 Ma (lower Cretaceous) and mean track lengths vary between 11.6 m and 13.9 m, mostly displaying unimodal distributions with narrow standard deviations. All apatite fission-track ages are younger than the corresponding sample stratigraphic age, indicating substantial post-depositional annealing of the apatite fission-tracks. This agrees with results from maturity modelling, which indicates 3500–7000 m eroded Devonian and Carboniferous sedimentary cover. Numerical modelling of apatite fission-track data predicts onset of exhumation and cooling not earlier than 320 Ma in the Rhenish massif and 300 Ma in the Ruhr Basin, generally followed by late Carboniferous–Triassic cooling to below 50–60°C. Rapid late Variscan cooling was followed by moderate Mesozoic cooling rates of 0.1–0.2°C/Ma, converting into denudation rates of <1 mm/a (assuming a stable geothermal gradient of 30°C/km). Modelling results also give evidence for some late Triassic and early Jurassic heating and/or burial, which is supported by sedimentary rocks of the same age preserved at the rim of the lower Rhine Basin and in the subsurface of the Central and Northern Ruhr Basin. Cenozoic exhumation and cooling of the Rhenish massif is interpreted as an isostatic response to former erosion and major base-level fall caused by the subsidence in the lower Rhine Basin.  相似文献   

Late Quaternary polycystine radiolarian datum events in the Sea of Okhotsk   总被引：2，自引：0，他引：2  

Alexander Matul  Andrea Abelmann  Ralf Tiedemann  Andre Kaiser  Dirk Nürnberg 《Geo-Marine Letters》2002,22(1):25-32

Five radiolarian datum events have been recorded in the Late Quaternary sediment section from the Sea of Okhotsk, using age assignments based on oxygen-isotope stratigraphy: the last occurrence datum (LOD) of Stylacontarium acquilonium (at about 329 ka), the LOD of Spongodiscus sp. (at about 287 ka), the LOD of Amphimelissa setosa (at about 72 ka), the LOD of Lychnocanoma nipponica sakaii (at about 28 ka), and the L. nipponica sakaii acme event (at about 72 ka). The LODs of S. acquilonium, Spongodiscus sp. and A. setosa appear to be synchronous in comparison with those in the Subarctic North Pacific, but the LOD and the acme event of L. nipponica sakaii show an apparent diachroneity with the corresponding North Pacific events.  相似文献