Oceanic eddies in synthetic aperture radar images     

Andrei Yu Ivanov  Anna I. Ginzburg 《Journal of Earth System Science》2002,111(3):281-295

Continuous observations since 1991 by using synthetic aperture radar (SAR) on board the Almaz1, ERS-1/2, JERS-1, and RADARSAT satellites support the well-known fact that oceanic eddies are distributed worldwide in the ocean. The paper is devoted to an evaluation of the potential of SAR for detection of eddies and vortical motions in the ocean. The classification of typical vortical features in the ocean detected in remote sensing images (visible, infrared, and SAR) is presented as well as available information on their spatial and temporal scales. Examples of the Almaz-1 and ERS-1/2 SAR images showing different eddy types, such as rings, spiral eddies of the open ocean, eddies behind islands and in bays, spin-off eddies and mushroom-like structures (vortex dipoles) are given and discussed. It is shown that a common feature for most of the eddies detected in the SAR images is a broad spectrum of spatial scales, spiral shape and shear nature. It is concluded that the spaceborne SARs give valuable information on ocean eddies, especially in combination with visible and infrared satellite data.  相似文献   

A Late Pleistocene Tephra Layer in the Southern Great Basin and Colorado Plateau Derived from Mono Craters, California     

David B. Madsen  Andrei M. Sarna-Wojcicki  Robert S. Thompson 《Quaternary Research》2002,57(3):382

A newly identified tephra in stratified deposits in southwestern Utah, dated 14,000 ¹⁴C yr B.P., may aid in correlating late Pleistocene deposits across parts of the southern Great Basin and west-central Colorado Plateau. Geochemical analyses of the ash suggest the tephra originated from Mono Craters, California, and most probably correlates with Wilson Creek ash #3. Because the ash is 2 mm thick 550 km from its source, the event may have been larger than others correlated to Mono Craters eruptions.  相似文献   

Key Late Cenozoic fluvial archives of eastern Europe: the Dniester, Dnieper, Don and Volga     

Andrei V. Matoshko 《Proceedings of the Geologists' Association. Geologists' Association》2004,115(2):141-173

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Late Quaternary faulting along the western margin of the Poronaysk Lowland in central Sakhalin, Russia     

Hiroyuki Tsutsumi  Yasuhiro Suzuki  Andrei I. Kozhurin  Mihail I. Strel'tsov  Takeyuki Ueki  Hideaki Goto  Koji Okumura  Rustam F. Bulgakov  Hiroyuki Kitagawa 《Tectonophysics》2005,407(3-4):257-268

Sakhalin Island straddles an active plate boundary between the Okhotsk and Eurasian plates. South of Sakhalin, this plate boundary is illuminated by a series of M_w 7–8 earthquakes along the eastern margin of the Sea of Japan. Although this plate boundary is considered to extend onshore along the length of Sakhalin, the location and convergence rate of the plate boundary had been poorly constrained. We mapped north-trending active faults along the western margin of the Poronaysk Lowland in central Sakhalin based on aerial photograph interpretation and field observations. The active faults are located east of and parallel to the Tym–Poronaysk fault, a terrane boundary between Upper Cretaceous and Neogene strata; the active faults appear to have reactivated the terrane boundary at depth in Quaternary time. The total length of the active fault zone on land is about 140 km. Tectonic geomorphic features such as east-facing monoclinal and fault scarps, back-tilted fluvial terraces, and numerous secondary faults suggest that the faults are west-dipping reverse faults. Assuming the most widely developed geomorphic surface in the study area formed during the last glacial maximum at about 20 ka based on similarities of geomorphic features with those in Hokkaido Island, we obtain a vertical component of slip rate of 0.9–1.4 mm/year. Using the fault dip of 30–60°W observed at an outcrop and trench walls, a net slip rate of 1.0–2.8 mm/year is obtained. The upper bound of the estimate is close to a convergence rate across the Tym–Poronaysk fault based on GPS measurements. A trenching study across the fault zone dated the most recent faulting event at 3500–4000 years ago. The net slip associated with this event is estimated at about 4.5 m. Since the last faulting event, a minimum of 3.5 m of strain, close to the strain released during the last event, has accumulated along the central portion of the active strand of the Tym–Poronaysk fault.  相似文献   

Preface     

Nils-Axel Mrner  Ian S. Stewart  Vladimir G. Trifonov  Andrei I. Kozhurin 《Tectonophysics》2004,380(3-4):v-vi

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Hydrodynamic modelling of mesoscale eddies in the Black Sea     

Cecilia E. Enriquez  Georgy I. Shapiro  Alejandro J. Souza  Andrei G. Zatsepin 《Ocean Dynamics》2005,55(5-6):476-489

A three dimensional structure of mesoscale circulation in the Black Sea is simulated using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System. A number of sensitivity tests reveal the response of the model to changes in the horizontal resolution, time steps, and diffusion coefficients. Three numerical grids are examined with x-fine (3.2 km), fine (6.7 km) and coarse (25 km) resolution. It is found that the coarse grid significantly overestimates the energy of the currents and is not adequate even for the study of basin-scale circulation. The x-fine grid, on the other hand, does not give significant advantages compared to the fine grid, and the latter is used for the bulk of simulations. The most adequate parameters are chosen from the sensitivity study and used to model both the basin-scale circulation and day-to-day variability of mesoscale currents for the months of May and June of 2000. The model is forced with actual wind data every 6 h and monthly climatic data for evaporation, precipitation, heat fluxes and river run-off. The results of the fine grid model are compared favourably against the satellite imagery. The model adequately reproduces the general circulation and many mesoscale features including cyclonic and anticyclonic eddies, jets and filaments in different parts of the Black Sea. The model gives a realistic geographical distribution and parameters of mesoscale currents, such as size, shape and evolution of the eddies.  相似文献   

Hierarchical aggregation in percolation model     

Ilya Zaliapin  Henry Wong  Andrei Gabrielov   《Tectonophysics》2006,413(1-2):93

There is a growing belief that the complex dynamics of seismicity can be better understood by studying the collective behavior of numerous lithosphere instability sources rather than focusing on the details of each of them. Classical site-percolation is a simple and tractable model which exhibits such important general features of complex systems as criticality and phase transitions of second kind. It also illustrates the mechanism of hierarchical aggregation, which is very important for explaining collective phenomena in material fracture and earthquake nucleation processes. We study the dynamics of a 2D site percolation model on a square lattice using the hierarchical approach introduced by Gabrielov et al., Phys. Rev. E., 5293–5300, 1999. The key elements of the approach are the tree representation of clusters and the Horton–Strahler scheme for cluster ranking. Accordingly, the evolution of percolation model is considered as a hierarchical inverse cascade of cluster aggregation. We analyzed the growth of the percolation cluster and established the time-dependent rank distribution of its subclusters, as well as corresponding laws for its mass, rank, and their relationship. We report several phenomena premonitory to the onset of percolation that complement the traditional power-law increase of the model's observables. In addition, we have shown that the Tokunaga side-branching constraint uniquely determines the mass–rank relationship for a general aggregation process (not necessarily originated from the percolation model). The results can be used for development and improvement of earthquake prediction techniques.  相似文献   

Late Pleistocene to Holocene vegetation and climate changes in northwestern Chukotka (Far East Russia) deduced from lakes Ilirney and Rauchuagytgyn pollen records     

Andrei A. Andreev  Elena Raschke  Boris K. Biskaborn  Stuart A. Vyse  Jeremy Courtin  Thomas Böhmer  Kathleen Stoof-Leichsenring  Stefan Kruse  Lyudmila A. Pestryakova  Ulrike Herzschuh 《Boreas: An International Journal of Quaternary Research》2021,50(3):652-670

This paper presents two new pollen records and quantitative climate reconstructions from northern Chukotka documenting environmental changes over the last 27.9 ka. Open tundra- and steppe-like habitats dominated between 27.9 and 18.7 cal. ka BP. Betula and Alnus shrubs might have grown in sheltered microhabitats but disappeared after 18.7 cal. ka BP. Although the climate was rather harsh, local herb-dominated communities supported herbivores as is evident by the presence of coprophilous spores in the sediments. The increase in Salix and Cyperaceae ~16.1 cal. ka BP suggests climate amelioration. Shrub Betula appeared ~15.9 cal. ka BP, and became dominant after ~15.52 cal. ka BP, whilst typical steppe communities drastically reduced. Very high presence of Botryococcus in the Lateglacial sediments reflects widespread shallow habitats, probably due to lake level increase. Shrub Alnus became common after ~13 cal. ka BP reflecting further climate amelioration. Simultaneously, herb communities gradually decreased in the vegetation reaching a minimum ~11.8 cal. ka BP. A gradual decrease of algae remains suggests a reduction of shallow-water habitats. Shrubby and graminoid tundra was dominant ~11.8–11.1 cal. ka BP, later Salix stands significantly decreased. The forest-tundra ecotone established in the Early Holocene, shortly after 11.1 cal. ka BP. Low contents of green algae in the Early Holocene sediments likely reflect deeper aquatic conditions. The most favourable climate conditions were between ~10.6 and 7 cal. ka BP. Vegetation became similar to the modern after ~7 cal. ka BP but Pinus pumila came to the Ilirney area at about 1.2 cal. ka BP. It is important to emphasize that the study area provided refugia for Betula and Alnus during MIS 2. It is also notable that our records do not reflect evidence of Younger Dryas cooling, which is inconsistent with some regional environmental records but in good accordance with some others.  相似文献   

Interpretation case study of the Sahl El Qaa area, southern Sinai Peninsula, Egypt     

Taha Rabeh  Jorge Miguel Miranda  Joao Carvalho  Andrei Bocin 《Geophysical Prospecting》2009,57(3):447-459

The study area is located in the Sinai Peninsula, which is considered one of the most promising regions for oil resources. Three different tectonic forces affect the area in the triple junction structures associated with the opening of the Gulf of Suez and the strike slip movement along the Gulf of Aqaba. The main goal of this work is to model the structure of the basement rocks in the study area using magnetic methods. To achieve this, a high-resolution land magnetic survey was acquired and the results were combined with existing seismic reflection data. The magnetic interpretation was carried out using the analytical signal, horizontal gradient, Euler and Werner deconvolution and 3D magnetic modelling methods. We concluded that most of the deduced structures are trending in N–S, N35°–N45° west and E–W directions. The Aqaba trend (N15°–N25° east) is barely noticeable. The depth to the basement rocks ranges from 1 km to more than 2 km below sea level and these results are in agreement with the available well log data. In addition, interpretation of seismic reflection sections was carried out and compared with overlapping magnetic profiles interpreted using Euler deconvolution. They show that the sedimentary section was affected by the basement tectonics, with faults extending from the basement upwards through the sedimentary cover. These faults constitute good potential structural traps for oil accumulation.  相似文献   

Design of passive systems for control of inelastic structures     

Gian Paolo Cimellaro  Oren Lavan  Andrei M. Reinhorn 《地震工程与结构动力学》2009,38(6):783-804

A design strategy for control of buildings experiencing inelastic deformations during seismic response is formulated. The strategy is using weakened, and/or softened, elements in a structural system while adding passive energy dissipation devices (e.g. viscous fluid devices, etc.) in order to control simultaneously accelerations and deformations response during seismic events. A design methodology is developed to determine the locations and the magnitude of weakening and/or softening of structural elements and the added damping while insuring structural stability. A two‐stage design procedure is suggested: (i) first using a nonlinear active control algorithm, to determine the new structural parameters while insuring stability, then (ii) determine the properties of equivalent structural parameters of passive system, which can be implemented by removing or weakening some structural elements, or connections, and by addition of energy dissipation systems. Passive dampers and weakened elements are designed using an optimization algorithm to obtain a response as close as possible to an actively controlled system. A case study of a five‐story building subjected to El Centro ground motion, as well as to an ensemble of simulated ground motions, is presented to illustrate the procedure. The results show that following the design strategy, a control of both peak inter‐story drifts and total accelerations can be obtained. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献