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111.
Sediment thickness was evaluated on the western flank of the East Pacific Rise (EPR) at 45°S, based on high-resolution seismic data gathered during cruise 213/2 of R/V Sonne in 2011. Two zones with distinctly different sediment thickness were identified, separated by a transitional zone bordering a pseudo-fault. Sediment in the more distal zone 2 is almost twice as thick (~120 m) as in zone 1 close to the EPR. This is in contrast to the expected progressive sedimentary column thickening with seafloor age and distance from the spreading axis. The younger of two seismic units detected within the sedimentary column (EPR-2) occurs mainly in the distal zone on crust older than 9 Ma, whereas on younger crust it is present only in small isolated bodies. Both sedimentary units drape the basement. The drape is interpreted to represent particle settling from suspension and a generally low regional primary productivity. The spatial variation in sediment thickness cannot be explained by existing models, and other processes considered in the present case are (1) higher productivity in the western sector of the survey area, where thicker sediments were observed (zone 2), (2) the formation of sediment drifts near basement highs (‘seamount effect’), due to flow of Lower Circumpolar Deep Water affecting sediment deposition, and (3) erosion and/or non-deposition of the younger EPR-2 unit, due to elevated bed shear stresses associated with eddies transferring kinetic energy to the seafloor 相似文献
112.
Research on gas hydrate has increased recently as an alternative to fossil fuel. This study of marine controlled source electromagnetics (CSEM) is motivated by this increase, particularly in deep waters, and examines representative models. We present 2D models and test their efficacy in detection and characterization of gas hydrates. Earlier modeling studies used a horizontal transmitter to study the CSEM response??two electrical and one magnetic component??for resistive subsurface layers. Here we use six components??three electrical and three magnetic??and show that the proposed method reduces ambiguity in interpretation. Additionally, we show results utilizing the transmitter dipole in a borehole and receivers at the sea bottom. We found that CSEM response from a vertical transmitter helps us characterize resistive layers more confidently than from a transmitter moving horizontally at sea bottom. We conclude that in a complex environment, combining horizontal and vertical movements of the transmitter with sea-bottom receivers helps us delineate the subsurface structure more clearly and may help reduce drilling costs. Our models closely match the gas hydrate region in the Gulf of Mexico??Walker Ridge Block-313. Although this study examines gas hydrate, the methodology is applicable to other areas??for example, in monitoring gas diffusion at subsurface depths, which may help in CO2 sequestration. 相似文献
113.
Gabriele Procaccini Sven Beer Mats Björk Jeanine Olsen Silvia Mazzuca Rui Santos 《Marine Ecology》2012,33(4):522-527
In March 2011, the Ecophysiology and Genetics Working Groups of the European Science Foundation COST Action ES 0906, entitled Seagrass Productivity: From Genes to Ecosystem Management, organized an exploratory workshop entitled “Linking Ecophysiology and Ecogenomics in Seagrass Systems”. The goal of the workshop was to discuss how to integrate comparative gene expression studies with physiological processes such as photosynthetic performance, carbon and nitrogen utilization and environmental adaptation. The main questions discussed for integrative research related to mechanisms of carbon utilization, light requirements, temperature effects and natural variation in pH and ocean acidification. It was concluded that the seagrass research community is still in the nascent stages of linking ecophysiology with genomic responses, as carbon and nitrogen metabolism of seagrasses have not been sufficiently well studied. Likewise, genomic approaches have only been able to assign meaningful interpretations to a handful of differentially expressed genes. Nevertheless, the way forward has been established. 相似文献
114.
Impact of model development,calibration and validation decisions on hydrological simulations in West Lake Erie Basin 总被引:1,自引:0,他引:1
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Prasad Daggupati Haw Yen Michael J. White Raghavan Srinivasan Jeffrey G. Arnold Conor S. Keitzer Scott P. Sowa 《水文研究》2015,29(26):5307-5320
Watershed simulation models are used extensively to investigate hydrologic processes, landuse and climate change impacts, pollutant load assessments and best management practices (BMPs). Developing, calibrating and validating these models require a number of critical decisions that will influence the ability of the model to represent real world conditions. Understanding how these decisions influence model performance is crucial, especially when making science‐based policy decisions. This study used the Soil and Water Assessment Tool (SWAT) model in West Lake Erie Basin (WLEB) to examine the influence of several of these decisions on hydrological processes and streamflow simulations. Specifically, this study addressed the following objectives (1) demonstrate the importance of considering intra‐watershed processes during model development, (2) compare and evaluated spatial calibration versus calibration at outlet and (3) evaluate parameter transfers across temporal and spatial scales. A coarser resolution (HUC‐12) model and a finer resolution model (NHDPlus model) were used to support the objectives. Results showed that knowledge of watershed characteristics and intra‐watershed processes are critical to produced accurate and realistic hydrologic simulations. The spatial calibration strategy produced better results compared to outlet calibration strategy and provided more confidence. Transferring parameter values across spatial scales (i.e. from coarser resolution model to finer resolution model) needs additional fine tuning to produce realistic results. Transferring parameters across temporal scales (i.e. from monthly to yearly and daily time‐steps) performed well with a similar spatial resolution model. Furthermore, this study shows that relying solely on quantitative statistics without considering additional information can produce good but unrealistic simulations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
115.
Roberto De Ferrari Gabriele Ferretti Simone Barani Daniele Spallarossa 《Soil Dynamics and Earthquake Engineering》2010
This paper presents a comprehensive ground response study for the municipality of Villa Collemandina in Northern Tuscany (Italy). This site was selected following a macroseismic analysis of the 1920 Garfagnana earthquake (Mw=6.5), which, at Villa Collemandina, produced damage and losses that were larger than at any other site near the earthquake epicentre, thus indicating the presence of possible site effects. Hence, both experimental and numerical methods are applied in order to investigate the ground response at different locations within the Villa Collemandina municipality. Results obtained from the spectral analysis of earthquake recordings using the reference site method and those from a 2-dimensional dynamic simulation reveal the presence of site effects due to the buried geomorphology (basin-like effects), allowing us to explain the severe damage and losses produced by the 1920 Garfagnana earthquake. As a further result, horizontal to vertical spectral ratio techniques and 1D soil modelling are proved to be inadequate for an effective characterization of the ground response at sites that, like Villa Collemandina, present a complex local geology. 相似文献
116.
Chiara Turino Paola Morasca Gabriele Ferretti Davide Scafidi Daniele Spallarossa 《Journal of Seismology》2010,14(2):393-411
Reliable automatic procedure for locating earthquake in quasi-real time is strongly needed for seismic warning system, earthquake
preparedness, and producing shaking maps. The reliability of an automatic location algorithm is influenced by several factors
such as errors in picking seismic phases, network geometry, and velocity model uncertainties. The main purpose of this work
is to investigate the performances of different automatic procedures to choose the most suitable one to be applied for the
quasi-real-time earthquake locations in northwestern Italy. The reliability of two automatic-picking algorithms (one based
on the Characteristic Function (CF) analysis, CF picker, and the other one based on the Akaike’s information criterion (AIC),
AIC picker) and two location methods (“Hypoellipse” and “NonLinLoc” codes) is analysed by comparing the automatically determined
hypocentral coordinates with reference ones. Reference locations are computed by the “Hypoellipse” code considering manually
revised data and tested using quarry blasts. The comparison is made on a dataset composed by 575 seismic events for the period
2000–2007 as recorded by the Regional Seismic network of Northwestern Italy. For P phases, similar results, in terms of both
amount of detected picks and magnitude of travel time differences with respect to manual picks, are obtained applying the
AIC and the CF picker; on the contrary, for S phases, the AIC picker seems to provide a significant greater number of readings
than the CF picker. Furthermore, the “NonLinLoc” software (applied to a 3D velocity model) is proved to be more reliable than
the “Hypoellipse” code (applied to layered 1D velocity models), leading to more reliable automatic locations also when outliers
(wrong picks) are present. 相似文献
117.
Martina Demuro Duane G. Froese Lee J. Arnold Richard G. Roberts 《Quaternary Research》2012,77(2):305-316
Improved chronological control on the penultimate advance of the Cordilleran Ice Sheet in northwest Canada (the Reid glaciation) is required for a better understanding of late Quaternary palaeoclimatic and palaeoenvironmental change in eastern Beringia. However, reliable dating of glaciation events beyond the last glacial maximum is commonly hindered by a lack of directly dateable material. In this study we (i) provide the first combined minimum and maximum age constraint on the Reid glaciation at Ash Bend, its reference locale in the Stewart River valley, northwestern Canadian Cordillera, using single-grain optically stimulated luminescence dating of quartz; and (ii) compare the timing of the Reid glaciation with other penultimate ice sheet advances in the region with the aim of establishing improved glacial reconstructions in eastern Beringia. We obtain ages of 158 ± 18 ka and 132 ± 18 ka for glaciofluvial sands overlying and underlying the Reid till, respectively. These ages indicate that the Reid advance, at its reference locale, occurred during MIS 6. This precludes an earlier MIS 8 age, and suggests that the Reid advance may have been synchronous with the Delta glaciation of central Alaska, and is likely correlative with the Mirror Creek glaciation in southern Yukon. 相似文献
118.
Maurizio?Romanelli Francesco?Di BenedettoEmail author Laura?Bartali Massimo?Innocenti Gabriele?Fornaciai Giordano?Montegrossi Luca?A.?Pardi Alfonso?Zoleo Fabio?Capacci 《Physics and Chemistry of Minerals》2012,39(6):479-490
A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic
resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played
by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders
with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H+, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H+ (hAl) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical
processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested.
As a consequence, the hAl centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they
are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes. 相似文献
119.
120.
Gerard W. Hazeu Arnold K. Bregt Allard J.W. de Wit Jan G.P.W. Clevers 《International Journal of Applied Earth Observation and Geoinformation》2011
Land cover and land use are important information sources for environmental issues. One of the most important changes at the Earth's surface concerns land cover and land use. Knowledge about the location and type of these changes is essential for environmental modeling and management. Remote sensing data in combination with additional spatial data are recognized as an important source of information to detect these land cover and land use changes. 相似文献