Seismicity and codaQ values in the eastern Pyrenees: First results from the La Cerdanya seismic network     

Antoni M. Correig  Brian J. Mitchell  Ramon Ortiz 《Pure and Applied Geophysics》1990,132(1-2):311-329

Seismicity in the La Cerdanya region of the eastern Pyrenees has been accurately mapped for the first time using data from a local seismic network. The majority of earthquakes lies on or near the La Cerdanya fault or secondary faults to the south. Coda magnitudes determined for these earthquakes, using magnitude relations from other regions, range between –0.5 and 2.2. These are, however, presumed to be underdetermined values sinceQ values appear to be very low in the La Cerdanya region. CodaQ values at a frequency of 1.5 Hz range between 17 and 120, the lowest values being obtained for the most seismically active regions. CodaQ values also increase with increasing distance, a result which indicates decreasing seismic attenuation with increasing depth in the crust.  相似文献   

The impact of otter trawling on mud communities in the northwestern Mediterranean   总被引：1，自引：2，他引：1  

Sanchez  P.; Demestre  M.; Ramon  M.; Kaiser  M. J. 《ICES Journal of Marine Science》2000,57(5):1352-1358

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Rockfall susceptibility zoning at a large scale: From geomorphological inventory to preliminary land use planning   总被引：3，自引：0，他引：3  

Ramon Copons  Joan M. Vilaplana   《Engineering Geology》2008,102(3-4):142

Rockfall, up to several hundreds of cubic meters, is a frequent and rapid landslide which menaces extensive areas in mountainous territories. Rockfall susceptibility zoning map at a large scale (1:5000–1:25 000) can be the first tool for land use planning in order to manage rockfall risk. A methodology allowing to analyze susceptibility in extensive areas with optimum cost/benefit relationship is needed. This work analyzes rockfall susceptibility in an extensive rocky mountain of the Principality of Andorra (Pyrenees Mountains), first on the rock slope and then on the exposed area located below. The rockfall record, obtained by means of geomorphological analysis, supplies the main data to analyze the susceptibility on the rock slope. An additional historical inventory verifies the accuracy of rockfall sizes recorded by means of the geomorphological analysis. According to the classification recommended by the Guidelines of Joint Technical Committee, the density of rockfall features on the rock slope assesses susceptibility in four levels. Subsequently, susceptibility on exposed areas has been analyzed by means of reach probability of rock blocks analysis using empirical models. Data acquired from thirteen recent events, from 1999 to 2004, have been used to verify the accuracy of the two empirical models mainly used (reach angle and shadow angle). Five reach probability limits (1, 0.5, 0.25, 0.01, and 0) establish boundaries between susceptibility levels. The resulting rockfall susceptibility zoning map allows: (a) to identify land areas and human elements exposed to rockfalls and, (b) to establish several exposition levels. This map can be a useful and cost-effective tool for administrations responsible to manage natural risk in order to guide urban grow in extensive areas or decide upon work programs based on in-depth analysis (hazard and risk).  相似文献   

Ground-Water Age Distribution in Madrid Basin, Spain   总被引：1，自引：0，他引：1  

M. Ramon Llamas  Eugene S. Simpson  Pedro E. Martinez Alfaro 《Ground water》1982,20(6):688-695

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Plate tectonics and volcanism in the gibraltar arc     

Vicente Araña  Ramon Vegas 《Tectonophysics》1974,24(3):197-212

Late Tertiary and Quaternary volcanism of southeastern Spain can be fitted in a platetectonics model, taking into account the post-Paleozoic evolution of the stable and semimobile Iberian areas and the new orogenic belts bordering the Mediterranean between Africa and the Iberian Peninsula.The occurrence and distribution of calc-alkaline and potassic volcanism suggest an oceanic crust sinking downwards from the Iberian plate. This active margin is causally related to the convergence and collision of Iberia and Africa during Late Cretaceous—Early Miocene time span.A pre-collision distensive phase is inferred from the stratigraphie and tectonic record between the Triassic and Late Cretaceous, while since the Late Miocene another distensive phase is related to the actualistic features.  相似文献   

Multi-component carbon isotope evidence of early Holocene environmental change and carbon-flow pathways from a hard-water lake in northern Sweden   总被引：4，自引：2，他引：2  

Dan Hammarlund  Ramon Aravena  Lena Barnekow  Bjørn Buchardt  Göran Possnert 《Journal of Paleolimnology》1997,18(3):219-233

A 9000-year carbonate-rich sediment sequence from a small hard-water lake in northernmost Sweden was studied by means of multi-component stable carbon isotope analysis. Radiocarbon dating of different sediment fractions provides chronologic control and reveals a rather constant hard-water effect through time, suggesting that the lake has remained hydrologically open throughout the Holocene. Successive depletion of ¹³C in fine-grained calcite and carbonate shells during the early Holocene correlate with a change in catchment vegetation from pioneer herb communities to boreal forest. The vegetational change and associated soil development likely gave rise to an increased supply of ¹³C-depleted carbon dioxide in groundwater recharging the lake. This process is therefore believed to be the main cause of decreasing values of ¹³C in dissolved inorganic carbon of the lake and thereby in limnic carbonates. Strongly ¹³C-depleted sedimentary organic matter may be related to enhanced kinetic fractionation during photosynthetic assimilation by means of proton pumping in Characean algae. This interpretation is supported by a substantial offset between ¹³C of DIC as recorded by mollusc shells and ¹³C of fine-grained calcite.  相似文献   

Detailed debris flow hazard assessment in Andorra: A multidisciplinary approach   总被引：14，自引：0，他引：14  

Marcel Hürlimann  Ramon Copons  Joan Altimir 《Geomorphology》2006,78(3-4):359-372

In many mountainous areas, the rapid development of urbanisation and the limited space in the valley floors have created a need to construct buildings in zones potentially exposed to debris flow hazard. In these zones, a detailed and coherent hazard assessment is necessary to provide an adequate urban planning. This article presents a multidisciplinary procedure to evaluate the debris flow hazard at a local scale. Our four-step approach was successfully applied to five torrent catchments in the Principality of Andorra, located in the Pyrenees. The first step consisted of a comprehensive geomorphologic and geologic analysis providing an inventory map of the past debris flows, a magnitude–frequency relationship, and a geomorphologic–geologic map. These data were necessary to determine the potential initiation zones and volumes of future debris flows for each catchment. A susceptibility map and different scenarios were the principal outcome of the first step, as well as essential input data for the second step, the runout analysis. A one-dimensional numerical code was applied to analyse the scenarios previously defined. First, the critical channel sections in the fan area were evaluated, then the maximum runout of the debris flows on the fan was studied, and finally simplified intensity maps for each defined scenario were established. The third step of our hazard assessment was the hazard zonation and the compilation of all the results from the two previous steps in a final hazard map. The base of this hazard map was the hazard matrix, which combined the intensity of the debris flow with its probability of occurrence and determined a certain hazard degree. The fourth step referred to the hazard mitigation and included some recommendations for hazard reduction. In Andorra, this four-step approach is actually being applied to assess the debris flow hazard. The final hazard maps, at 1 : 2000 scale, provide an obligatory tool for local land use planning. Experience achieved during the study showed that the collaboration between geologists, geomorphologists, engineers, and decision makers is essential and that only a multidisciplinary approach allows for solving all the problems of such a complex process as debris flows. Finally, we propose that our approach may be applied to other mountainous areas, adapting the hazard matrix to new local conditions.  相似文献   

Automatic GIS-based system for volcanic hazard assessment     

Alicia Felpeto  Joan Martí  Ramon Ortiz 《Journal of Volcanology and Geothermal Research》2007

This paper presents an automatic system for the elaboration of volcanic hazard maps and scenarios. The methodology used for the generation of both maps is based on the use of numerical simulation of eruptive processes. The system has been developed in a Geographical Information System (GIS) framework, where models for the numerical simulation of different volcanic hazards have been integrated. The user can select in a toolbar one hazard and then decide whether to generate a scenario map (usually with a unique vent) or a hazard map (generally with a broader source area). Once the input parameters are selected, the system automatically generates the corresponding map. The system also incorporates a module to determine the spatial probability of vent opening, as this could be an important parameter for the computation of hazard maps. The tool has been designed in such a way that the inclusion of new numerical models and functionalities is rather easy. Each numerical model is programmed and implemented as an independent program that is launched from the system and, when it finishes the computation, returns the control to the GIS, where the results are shown. This structure allows that further analyses (specifically, risk analyses, that use as an input a hazard or a scenario map), could be also automated inside the system. Additional information, including tutorial and downloadable files can be found in www.gvb-csic.es.  相似文献   

    

M. Ramon Llamas 《Hydrogeology Journal》2006,14(1-2):264

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On the nature of mantle heterogeneities and discontinuities: evidence from a very dense wide-angle shot record     

Ramon Carbonell   《Tectonophysics》2004,388(1-4):103

A seismic survey with a receiver spacing of 50 m provided one of the most densely sampled wide-angle seismic reflection images of the lithosphere. This unique data set, recorded by an 18-km-long spread, reveals that at wide-angles the shallow subcrustal mantle features high amplitude reflectivity which contrasts with a lack of reflectivity at latter travel times. This change in the seismic signature is located at approximately 120–150 km depth, which correlates with the depth estimates of the lithosphere–asthenosphere boundary (LAB) of previous DSS studies. This seismic signature can be simulated by two-layer mantle model. Both layers with similar average velocities differ in their degree of heterogeneity. The shallow heterogeneous layer and the deeper and more homogeneous one correlate with the lithosphere and the asthenosphere, respectively. Studies involving surface outcrops of ultramafic massifs and mantle xenoliths infer that the upper mantle is a heterogeneous mixture of ultramafic rocks (lherzolites, harzburgites, pyroxenites, peridotites, dunites, and small amounts of eclogites). Laboratory measurements of physical properties of these mantle rocks indicate that compositional variations alone can account for the wide-angle reflectivity. A temperature increase would homogenize the mixture, decreasing the seismic reflection properties due to melting processes. It is proposed that this would take place below 120–150 km (1200 °C, the LAB).  相似文献