Multiparametric Traveltime Inversion     

Biloti  Ricardo  Santos  Lúcio T.  Tygel  Martin 《Studia Geophysica et Geodaetica》2002,46(2):177-192

In conventional seismic processing, the classical algorithm of Hubral and Krey is routinely applied to extract an initial macrovelocity model that consists of a stack of homogeneous layers bounded by curved interfaces. Input for the algorithm are identified primary reflections together with normal moveout (NMO) velocities, as derived from a previous velocity analysis conducted on common midpoint (CMP) data. This work presents a modified version of the Hubral and Krey algorithm that is designed to extend the original version in two ways, namely (a) it makes an advantageous use of previously obtained common-reflection-surface (CRS) attributes as its input and (b) it also allows for gradient layer velocities in depth. A new strategy to recover interfaces as optimized cubic splines is also proposed. Some synthetic examples are provided to illustrate and explain the implementation of the method.  相似文献   

Stresses and strains in a twisted subduction zone—Fiordland, New Zealand     

Martin Reyners  Russell Robinson  Aasha Pancha  Peter McGinty 《Geophysical Journal International》2002,148(3):637-648

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Identification of geomorphic process units in Kärkevagge, northern Sweden, by remote sensing and digital terrain analysis     

Annett Bartsch  Martin Gude  Christer Jonasson  & Dieter Scherer 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):171-178

Sediment transport processes in the Kärkevagge are investigated concerning their spatial and temporal characteristics due to long–term monitoring. Within this study remote sensing techniques and GIS modelling in connection with geomorphic mapping are applied for identification and characterization of geomorphic process units. Relationships between geomorphometric parameters and slope processes like solifluction, talus creep and rockfall have been analysed. Multitemporal Landsat–TM5 scenes are used as source for landcover characteristics (Normalized Difference Vegetation Index) after preprocessing involving orthorectification and topographic normalization in order to remove possible terrain–induced effects. Additionally, a digital elevation model with a resolution of 20 m for the Kärkevagge catchment is developed and parameters like slope gradient, slope aspect and profile curvature are extracted as input for the analysis of the sediment transport system. The combination of landcover information, geomorphometrical and topological features allows the definition of areas for single process activities. They show specific sediment displacement characteristics depending on material conditions, topological and geometrical features. Geomorphic process units, which show a homogenous composition, are extracted from these available layers.  相似文献   

Sea cliffs resulting from late Miocene extensional tectonics: the Serra Gelada case study (Betic Cordillera, Spain)     

Alfonso Ybenes  Pedro Alfaro  Jos Delgado  Antonio Estvez  Jesús M. Soria 《Geomorphology》2002,42(3-4)

The Serra Gelada sea cliffs are carved in Mesozoic carbonate rocks belonging to the External Zones of the eastern Betic Cordillera (Alicante, SE Spain). Several normal faults with vertical slips of more than a hundred metres have played an important role in the origin of this coastline. Some previous studies propose that the present cliff morphology was mainly originated by Quaternary fault activity. However, the integration of geomorphological features, stratigraphical and sedimentological data, together with the results of the tectonic analysis of fractures occurring in Serra Gelada, and a detailed study of seismic reflection profiles carried out in the adjacent continental shelf, indicate that these normal faults were active mainly during the late Miocene. Therefore, the Serra Gelada sea cliffs represent a tectonically controlled long-term landscape. Thus, normal faults have not significantly modified the Serra Gelada relief since then. Furthermore, the northern part of the Serra Gelada cliff may be considered as an inherited pre-Quaternary relict palaeocliff since it has only undergone very little erosive recession.  相似文献   

Human Modification of the Geomorphically Unstable Salt River in Metropolitan Phoenix     

Martin Roberge 《The Professional geographer》2002,54(2):175-189

In‐stream gravel mining, massive bridge piers, and channelization have all contributed to the geomorphic instability of the Lower Salt River channel in Arizona. Dam closure, changing dam operating rules, and the frequent modification of the channel bed have decreased our ability to predict the Salt River hydrology. Engineering practice has adapted to this situation and to a public that is increasingly intolerant of service disruptions by constructing larger bridges and extending levees. Building these larger structures may be counterproductive; future construction should not constrict the channel and should re‐establish a braided river to decrease the energy available to the system.  相似文献   

Average strain rate in the Italian crust inferred from a permanent GPS network – II. Strain rate versus seismicity and structural geology     

Alessandro Caporali  Silvana Martin  Matteo Massironi 《Geophysical Journal International》2003,155(1):254-268

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Floodplain–river ecosystems: lateral connections and the implications of human interference     

Martin C. Thoms   《Geomorphology》2003,56(3-4):335

Floodplains are ecotones that form a transition between aquatic and terrestrial environments. These important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface. Hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system. This paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large Australian floodplain to a river channel, and the effects of land and water developments on these exchanges. The paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach—a recognition of the importance of the three disciplines hydrology, geomorphology and ecology. Large-scale water-resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the Lower Balonne floodplain, Australia. The magnitude, frequency and duration of flooding events have all been reduced. The construction of levees and water storages has also reduced the reactive floodplain surface area. The presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation. Annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less. Some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water-resources and floodplain developments.  相似文献   

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment     

Thomas Backhaus  Rolf Altenburger  sa Arrhenius  Hans Blanck  Michael Faust  Antonio Finizio  Paola Gramatica  Matthias Grote  Marion Junghans  Wiebke Meyer  Manuela Pavan  Tobias Porsbring  Martin Scholze  Roberto Todeschini  Marco Vighi  Helge Walter  L. Horst Grimme 《Continental Shelf Research》2003,23(17-19):1757

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.  相似文献   

Asymmetric one‐storey elastic systems with non‐linear viscous and viscoelastic dampers: Simplified analysis and supplemental damping system design     

Wen‐Hsiung Lin  Anil K. Chopra 《地震工程与结构动力学》2003,32(4):579-596

Investigated is the accuracy in estimating the response of asymmetric one‐storey systems with non‐linear viscoelastic (VE) dampers by analysing the corresponding linear viscous system wherein all non‐linear VE dampers are replaced by their energy‐equivalent linear viscous dampers. The response of the corresponding linear viscous system is determined by response history analysis (RHA) and by response spectrum analysis (RSA) extended for non‐classically damped systems. The flexible and stiff edge deformations and plan rotation of the corresponding linear viscous system determined by the extended RSA procedure is shown to be sufficiently accurate for design applications with errors generally between 10 and 20%. Although similar accuracy is also shown for the ‘pseudo‐velocity’ of non‐linear VE dampers, the peak force of the non‐linear VE damper cannot be estimated directly from the peak damper force of the corresponding linear viscous system. A simple correction for damper force is proposed and shown to be accurate (with errors not exceeding 15%). For practical applications, an iterative linear analysis procedure is developed for determining the amplitude‐ and frequency‐dependent supplemental damping properties of the corresponding linear viscous system and for estimating the response of asymmetric one‐storey systems with non‐linear VE dampers from the earthquake design (or response) spectrum. Finally, a procedure is developed for designing non‐linear supplemental damping systems that satisfy given design criteria for a given design spectrum. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Inelastic displacement ratios for evaluation of existing structures     

Jorge Ruiz‐García  Eduardo Miranda 《地震工程与结构动力学》2003,32(8):1237-1258

Results of a detailed statistical study of constant relative strength inelastic displacement ratios to estimate maximum lateral inelastic displacement demands on existing structures from maximum lateral elastic displacement demands are presented. These ratios were computed for single‐degree‐of‐freedom systems with different levels of lateral strength normalized to the strength required to remain elastic when subjected to a relatively large ensemble of recorded earthquake ground motions. Three groups of soil conditions with shear wave velocities higher than 180m/s are considered. The influence of period of vibration, level of lateral yielding strength, site conditions, earthquake magnitude, distance to the source, and strain‐hardening ratio are evaluated and discussed. Mean inelastic displacement ratios and those associated with various percentiles are presented. A special emphasis is given to the dispersion of these ratios. It is concluded that distance to the source has a negligible influence on constant relative strength inelastic displacement ratios. However, for periods smaller than 1s earthquake magnitude and soil conditions have a moderate influence on these ratios. Strain hardening decreases maximum inelastic displacement at a fairly constant rate depending on the level of relative strength for periods of vibration longer than about 1.0s while it decreases maximum inelastic displacement non‐linearly as the period of vibration shortens and as the relative‐strength ratio increases for periods of vibration shorter than 1.0s. Finally, results from non‐linear regression analyses are presented that provide a simplified expression to be used to approximate mean inelastic displacement ratios during the evaluation of existing structures built on firm sites. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献