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21.
Sheridan Michael F. Hubbard Bernard Carrasco-núñez Gerardo Siebe Claus 《Natural Hazards》2004,33(2):209-221
Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in North America. Its most recent catastrophic events involved the production of pyroclastic flows that erupted approximately 4,000, 8,500, and 13,000 years ago. The distribution of mapped deposits from these eruptions gives an approximate guide to the extent of products from potential future eruptions. Because the topography of this volcano is constantly changing computer simulations were made on the present topography using three computer algorithms: energy cone, FLOW2D, and FLOW3D. The Heim Coefficient (), used as a code parameter for frictional sliding in all our algorithms, is the ratio of the assumed drop in elevation (H) divided by the lateral extent of the mapped deposits (L). The viscosity parameter for the FLOW2D and FLOW3D codes was adjusted so that the paths of the flows mimicked those inferred from the mapped deposits. We modeled two categories of pyroclastic flows modeled for the level I and level II events. Level I pyroclastic flows correspond to small but more frequent block-and-ash flows that remain on the main cone. Level II flows correspond to more widespread flows from catastrophic eruptions with an approximate 4,000-year repose period. We developed hazard maps from simulations based on a National Imagery and Mapping Agency (NIMA) DTED-1 DEM with a 90 m grid and a vertical accuracy of ±30 m. Because realistic visualization is an important aid to understanding the risks related to volcanic hazards we present the DEM as modeled by FLOW3D. The model shows that the pyroclastic flows extend for much greater distances to the east of the volcano summit where the topographic relief is nearly 4,300 m. This study was used to plot hazard zones for pyroclastic flows in the official hazard map that was published recently. 相似文献
22.
Darren Ruddell Sharon L. Harlan Susanne Grossman-Clarke Gerardo Chowell 《Climatic change》2012,111(3-4):581-607
Understanding public perceptions of climate is critical for developing an effective strategy to mitigate the effects of human activity on the natural environment and reduce human vulnerability to the impacts of climate change. While recent climate assessments document change among various physical systems (e.g., increased temperature, sea level rise, shrinking glaciers), environmental perceptions are relatively under-researched despite the fact that there is growing skepticism and disconnect between climate science and public opinion. This study utilizes a socio-ecological research framework to investigate how public perceptions compared with environmental conditions in one urban center. Specifically, air temperature during an extreme heat event was examined as one characteristic of environmental conditions by relating simulations from the Weather Research and Forecast (WRF) atmospheric model with self-reported perceptions of regional and neighborhood temperatures from a social survey of Phoenix, AZ (USA) metropolitan area residents. Results indicate that: 1) human exposure to high temperatures varies substantially throughout metropolitan Phoenix; 2) public perceptions of temperature are more strongly correlated with proximate environmental conditions than with distal conditions; and 3) perceptions of temperature are related to social characteristics and situational variables. The social constructionist paradigm explains public perceptions at the regional scale, while experience governs attitude formation at the neighborhood scale. 相似文献
23.
Domínguez Jaime Suárez Gerardo Gorbatov Alexei Segura Fabio 《Journal of Seismology》2021,25(6):1427-1439
Journal of Seismology - A three-dimensional tomographic image of the seismic velocity structure in the crust and upper mantle of northwestern Nicaragua was performed using the back-projection... 相似文献
24.
Ju Bing Gu Defeng Herring Thomas A. Allende-Alba Gerardo Montenbruck Oliver Wang Zhengming 《GPS Solutions》2017,21(1):53-64
GPS Solutions - Orbital maneuvers are usually performed as needed for low earth orbiters to maintain a predefined trajectory or formation-flying configuration. To avoid unexpected discontinuities... 相似文献
25.
The Citlaltépetl Ignimbrite records one of the largest explosive events during the Holocene activity of Citlaltépetl Volcano
(Pico de Orizaba). Multiple pyroclastic flow units, a fall deposit, and some lahar units were emplaced between 8500–9000 y
B.P. as a result of repetitive but discrete explosive events. The whole ignimbrite resulted from discrete fluctuations in
eruptive intensity that decreased with time. The initial pyroclastic flow pulse was by far the most violent and widespread
event, and its deposits show conspicuous variations in structure and texture that could be associated with different mechanisms
of transport and emplacement. Subpopulation Sequential Fragmentation Transport (SFT) analyses were carried out in order to
determine the physical mechanisms that selectively concentrate or remove particles in the moving flows. We suggest that lateral
and temporal changes in the flow rheology, in which fluidization, yield strength, entrainment of atmospheric air, and sedimentation
played a dominant role in flow propagation and emplacement, may imprint a unique signature in the grain-size spectra. The
lowermost unit of the Citlaltépetl Ignimbrite can be envisaged by a model in which progressive aggradation near the vent became
replaced by en masse emplacement farther outward.
Received: 24 March 1998 / Accepted: 9 October 1998 相似文献
26.
Natural Hazards - Analysis of precipitation trends as well as the observed trends in precipitation concentration can be useful tools for the identification of natural hazards. This study aimed to... 相似文献
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Stefano De Santis Paolo Casadei Gerardo De Canio Gianmarco de Felice Marialaura Malena Marialuisa Mongelli Ivan Roselli 《地震工程与结构动力学》2016,45(2):229-251
An innovative solution for the seismic protection of existing masonry structures is proposed and investigated through shake table tests on a natural scale wall assemblage. After a former test series carried out without reinforcement, the specimen was retrofitted using Steel Reinforced Grout. The strengthening system comprises horizontal strips of ultra‐high strength steel cords, externally bonded to the masonry with hydraulic lime mortar, and connectors to transversal walls, applied within the thickness of the plaster layer. In order to assess the seismic performance of the retrofitted wall, natural accelerograms were applied with increasing intensity up to failure. Test results provide a deep understanding of the effectiveness of mortar‐based composites for improving the out‐of‐plane seismic capacity of masonry walls, in comparison with traditional reinforcements with steel tie‐bars. The structural implications of the proposed solution in terms of dynamic properties and damage development under earthquake loads are also discussed.Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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