An analysis and interpretation of the current data collected in the strait of Juan de Fuca in 1973     

Gabriel Godin  Julio Candela  René de la Paz‐Vela 《Marine Geodesy》2013,36(3):273-302

Abstract

We evaluate a set of current measurements done in a section of the Strait of Juan de Fuca. The flow is of estuarine character, the upper layer flow usually being directed seaward. The RMS value of steady current exceeds its mean value appreciably in the upper layer; it also exceeds the mean near the bottom. The near‐surface currents do change their direction on occasions and can run landward for over five consecutive days, especially in the southern part of the channel. The lower layer flow (landward) and the upper layer flow (seaward) varied in magnitude from 90 to 160 thousand m³/sec, and their fluctuations were in phase; their difference, the net flow, is of the order of 5% to 10% of these flows and could not be calculated with any confidence. Tidal motion is barotropic in the section, with some deformation in the vertical caused by bottom friction and internal stresses. The M₂ tide in the system Juan de Fuca‐Georgia Strait can be represented by a standing Kelvin wave influenced by friction. The K₁ tide can also be represented by a standing Kelvin wave if some leakage is allowed in the northern end of Georgia Strait. Topographic effects mask the Coriolis influence on the intensity of tidal currents.  相似文献   

Advancing Global Marine Biogeography Research with Open‐source GIS Software and Cloud Computing     

Ei Fujioka  Edward Vanden Berghe  Ben Donnelly  Julio Castillo  Jesse Cleary  Chris Holmes  Sean McKnight  Patrick Halpin 《Transactions in GIS》2012,16(2):143-160

Across many scientific domains, the ability to aggregate disparate datasets enables more meaningful global analyses. Within marine biology, the Census of Marine Life served as the catalyst for such a global data aggregation effort. Under the Census framework, the Ocean Biogeographic Information System was established to coordinate an unprecedented aggregation of global marine biogeography data. The OBIS data system now contains 31.3 million observations, freely accessible through a geospatial portal. The challenges of storing, querying, disseminating, and mapping a global data collection of this complexity and magnitude are significant. In the face of declining performance and expanding feature requests, a redevelopment of the OBIS data system was undertaken. Following an Open Source philosophy, the OBIS technology stack was rebuilt using PostgreSQL, PostGIS, GeoServer and OpenLayers. This approach has markedly improved the performance and online user experience while maintaining a standards‐compliant and interoperable framework. Due to the distributed nature of the project and increasing needs for storage, scalability and deployment flexibility, the entire hardware and software stack was built on a Cloud Computing environment. The flexibility of the platform, combined with the power of the application stack, enabled rapid re‐development of the OBIS infrastructure, and ensured complete standards‐compliance.  相似文献   

Heterozoan carbonate deposition on a steep basement escarpment (Late Miocene,Almería,south‐east Spain)          下载免费PDF全文

Fernando Sola  Ángel Puga‐Bernabéu  Julio Aguirre  Juan C. Braga 《Sedimentology》2017,64(4):1107-1131

Heterozoan temperate‐water carbonates mixed with varying amounts of terrigenous grains and muddy matrix (Azagador limestone) accumulated on and at the toe of an inherited escarpment during the late Tortonian–early Messinian (late Miocene) at the western margin of the Almería–Níjar Basin in south‐east Spain. The escarpment was the eastern end of an uplifting antiform created by compressive folding of Triassic rocks of the Betic basement. Channelized coralline‐algal/bryozoan rudstone to coarse‐grained packstone, together with matrix‐supported conglomerate, are the dominant lithofacies in the higher outcrops, comprising the deposits on the slope. These sediments mainly fill small canyon‐shaped, half‐graben depressions formed by normal faults active before, during and after carbonate sedimentation. Roughly bedded and roughly laminated coralline‐algal/bryozoan rudstone to coarse‐grained packstone are the main lithofacies forming an apron of four small (kilometre‐scale) lobes at the toe of the south‐eastern side of the escarpment (Almería area). Channelized and roughly bedded coralline‐algal/bryozoan rudstone to coarse‐grained packstone, conglomerates, packstone and sandy silt accumulated in a small channel‐lobe system at the toe of the north‐eastern side of the escarpment (Las Balsas area). Carbonate particles and terrigenous grains were sourced from shallow‐water settings and displaced downslope by sediment density flows that preferentially followed the canyon‐shaped depressions. Roughly laminated rudstone to packstone formed by grain flows on the initially very steep slope, whereas the rest of the carbonate lithofacies were deposited by high‐density turbidite currents. The steep escarpment and related break‐in‐slope at the toe favoured hydraulic jumps and the subsequent deposition of coarse‐grained, low‐transport efficiency skeletal‐dominated sediment in the apron lobes. Accelerated uplift of the basement caused a relative sea‐level fall resulting in the formation of outer‐ramp carbonates on the apron lobes, which were in turn overlain by lower Messinian coral reefs. The Almería example is the first known ‘base of slope’ apron within temperate‐water carbonate systems.  相似文献   

Site effects in Mexico City urban zone. A complementary study     

Francisco J. Chavez-Garcia  Julio Cuenca 《Soil Dynamics and Earthquake Engineering》1996,15(2):141

Site effects are a major factor affecting seismic risk at Mexico City conurbation and have been carefully studied. However, most of the studies and instrumentation concentrate in Mexico City. We present an evaluation of site effects in the counties of Estado de Mexico, to the North of Mexico City, that have been incorporated into Mexico City conurbation. We measured microtremors at 67 points and operated a temporal digital seismograph network. Our results allow us to extend the dominant period map of Mexico City to the heavily populated and industrialized counties of Estado de Mexico. Additionally, we propose a map of maximum relative amplification. Both maps are consistent with local geology, and could be useful for microzonation of this region.  相似文献   

Socio-spatial segregation and urban form: Belém at the end of the 1990s     

Jose Julio Lima   《Geoforum》2001,32(4):125

In the second half of the 1990s, socio-spatial segregation increased in Brazilian cities, accentuating inequity among social groups. Using a combination of space syntax techniques and statistical analysis, this paper explores locational differences in central and peripheral portions of Belém. The analysis shows how socio-spatial segregation was made more pronounced by relationships between urban form, infrastructure provision and locational values. Social groups' opportunities in the city are suggested to be limited by features of its urban form, associated with infrastructure provision, especially for groups unable to take advantage of intra-urban accessibility. The paper also discusses the findings of the study in relation to the Brazilian urban context at the end of the 1990s.  相似文献   

Petrographic and microthermometrical studies of emeralds in the ‘Garimpo’ of Capoeirana,Nova Era,Minas Gerais State,Brazil     

J. L. de Souza  J. C. Mendes  R. M. da Silveira Bello  D. P. Svisero  J. V. Valarelli 《Mineralium Deposita》1992,27(2):161-168

Petrographic investigations in the area of the Capoeirana emerald deposit, Minas Gerais State, revealed two main lithostructural units. The first unit is comprised of gneissic rocks of granitic composition belonging to the basement complex, and the second is composed of a highly weathered metasedimentary-metavolcanic sequence represented by metapelitic schists, amphibolites, schists derived from ultramafic rocks, and quartzites. Quartz and pegmatoid veins appear near the contacts between the gneissic rocks and the mineralization metasedimentary-metavolcanic sequence. The emerald mineralization is dominantly concentrated within the intercalations of meta-ultramafic schists near the contact of the pegmatoid veins. Microthermometric studies of the fluid inclusions of the emerald grains indicate that crystallization occurred in the pressure and temperature ranges of 2000 to 2750 bar and 450 to 650 °C, respectively. These data suggest that the mineralizing solutions have had a late hydrothermal-pneumatolytic origin characterized by low pressures, suggestive of the paragenesis talc + tremolite + carbonate + biotite-phlogopite + chlorite of the emerald wall rocks.  相似文献   

Temporal variability of throughfall as a function of the canopy development stage: from seasonal to intra-event scale     

José Bandeira Brasil  Eunice Maia de Andrade  Helba Araújo de Queiroz Palácio  Julio Cesar Neves dos Santos  Pedro Henrique Augusto Medeiros 《水文科学杂志》2020,65(10):1640-1651

ABSTRACT

The interception process impacts rainfall magnitude and intensity under the canopy. In this study, the effect of plant interception on throughfall characteristics was assessed in the deciduous Caatinga vegetation, at different canopy development stages and for temporal scales ranging from seasonal to the intra-event scale. Throughfall and stemflow percentages were slightly higher at the onset of the rainy season, when leaf area density is low, with resulting lower interception losses. However, there was no statistical difference among the variables at the seasonal scale. At the intra-event scale, average and maximum throughfall intensity at different time intervals showed statistical difference between the stages of canopy development. Regardless of leaf area density and rainfall depth, vegetation is able to retain all the water up to 2 min in the beginning of each rainfall event with accumulated rainfall smaller than 0.6 mm. Furthermore, the Caatinga vegetation attenuates the rainfall intensity by 30–40%.  相似文献   

Elastic Ray-Born L₂-Migration/Inversion     

Wafik B. Beydoun  Manuela Mendes 《Geophysical Journal International》1989,97(1):151-160

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Ground Motion Zoning of Santiago de Cuba: An Approach by SH Waves Modelling   总被引：3，自引：0，他引：3  

Leonardo Alvarez  Julio García  Franco Vaccari  Giuliano F. Panza  Bertha González  Carmen Reyes  Bárbara Fernández  Ramón Pico  José A. Zapata  Enrique Arango 《Pure and Applied Geophysics》2004,161(5-6):1041-1059

— The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic zoning of the city. Three different main zones are identified, and a small sector characterized by major resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake (M_S=7), and for the maximum possible (M_S=8).  相似文献   

Pace and Pattern of Recent Treeline Dynamics: Response of Ecotones to Climatic Variability in the Spanish Pyrenees   总被引：4，自引：0，他引：4  

J. Julio Camarero  Emilia Gutiérrez 《Climatic change》2004,63(1-2):181-200

Treeline ecotones are regarded as sensitive monitors of the recent climatic warming. However, it has been suggested that their sensitivity depends more on changes in tree density than on treeline position. We study these processes and the effect of climate, mainly air temperature, on tree recruitment and recent treeline dynamics. We selected three relatively undisturbed sites in the Spanish Pyrenees, dominated by Pinusuncinata, and analyzed their recent dynamics at local spatial (0.3–0.5 ha) and short temporal scales (100–300 years). We wanted to establish whether higher temperature was the only climatic factor causing an upward shift of the studied alpine treelines. The data we report show that treelines were ascending until a period of high interannual variability in mean temperature started (1950–95). During the late twentieth century, treeline fluctuation was less sensitive to climate than was the change in tree density within the ecotone. Tree recruitment and treeline position responded to contrasting climatic signals; tree recruitment was favored by high March temperatures whereas treeline position ascended in response to warm springs. We found a negative relationship between mean treeline-advance rate and March temperature variability. According to our findings, if the interannual variability of March temperature increases, the probability of successful treeline ascent will decrease.  相似文献