The amplitude domain analysis applied to the major Vrancea (Romania) earthquake of 30 August 1986 leads to the determination of some parameters characterizing the amplitude and the time duration of the signal.Digital three-component acceleration data, obtained at 10 Romanian seismic stations with epicentral distances between 40 and 200 km, are used. The results are compared with those obtained by Schenk for strong Californian earthquakes.Paper presented in the 21st General Assembly of the European Seismological Commission, Sofia, 1988. 相似文献
Playa lake systems tend to be overlooked archives of paleoenvironmental change due to the likelihood of a short and intermittent record of deposition. Groundwater-fed wetlands associated with these climate-sensitive playas, however, preserve changes in hydrologic budget and are thus valuable archives for semiarid regions. This study examines the paleoecological record of a groundwater-fed wetland from Lake Solai, Kenya. Biological proxies are used to reconstruct paleoenvironmental change and climate impacts over the past millennium. Dry conditions persisted between CE 1115 and 1490, followed by wetter conditions during the Little Ice Age. Near surface sediments indicate increasing anthropogenic impact through pastoralism. 相似文献
In the coastal waters off northern California, seasonal wind-driven upwelling supplies abundant nutrients to be processed by phytoplankton productivity. As part of the Coastal Ocean Processes: Wind Events and Shelf Transport (CoOP WEST) study, nutrients, CO2, size-fractionated chlorophyll, and phytoplankton community structure were measured in the upwelling region off Bodega Bay, CA, during May–June 2000, 2001 and 2002. The ability of this ecosystem to assimilate nitrate (NO3) and silicic acid/silicate (Si(OH)4) and accumulate particulate material (i.e. phytoplankton) was realized in all 3 years, following short events of upwelling-favorable winds, followed by periods of relaxed winds. This was observed as phytoplankton blooms, dominated by chlorophyll in cells greater than 5 μm in diameter, that reduced the ambient nutrients to zero. These communities were located over the near-shore shelf (<100 m depth) and were dominated by diatoms. An optimal window of 3–7 days of relaxed winds, following an upwelling pulse, was required for chlorophyll accumulation. The large-celled phytoplankton that result are likely important players in coastal new production and carbon cycling. 相似文献
Recent R-matrix calculations of electron impact excitation rates in Mg-like Fe xv are used to derive theoretical emission-line ratios involving transitions in the 243–418 Å wavelength range. A comparison of these with a data set of solar active region, subflare and off-limb spectra, obtained during rocket flights by the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS), reveals generally very good agreement between theory and observation, indicating that most of the Fe xv emission lines may be employed with confidence as electron density diagnostics. In particular, the 312.55-Å line of Fe xv is not significantly blended with a Co xvii transition in active region spectra, as suggested previously, although the latter does make a major contribution in the subflare observations. Most of the Fe xv transitions which are blended have had the species responsible clearly identified, although there remain a few instances where this has not been possible. We briefly address the long-standing discrepancy between theory and experiment for the intensity ratio of the 3s2 1S–3s3p 3P1 intercombination line at 417.25 Å to the 3s2 1S–3s3p 1P resonance transition at 284.16 Å. 相似文献
Our understanding of how groundwater mediates evapotranspiration/streamflow partitioning is still fragmented and catchment studies under changing vegetation conditions can provide a useful frame for integration. We explored this partition in a flat sedimentary dry catchment in central Argentina in which the replacement of native vegetation with rainfed crops was accompanied by the abrupt formation of groundwater-fed streams by subsurface erosion (i.e., sapping) episodes. Historical records indicated widespread water table rises (~0.3 m y−1 on average). Groundwater level and stream baseflow fluctuated seasonally with minima in the warm rainy season, indicating that evaporative discharge rather than rainfall shapes saturated flows. Diurnal groundwater level fluctuations showed that plant uptake was widespread where water tables are shallow (<3 m) but restricted to deep-rooted Prosopis forests where they are deep (7–10 m). MODIS and LANDSAT NDVI revealed a long-term greening for native vegetation, new wetlands included, but not for croplands, suggesting more limited evapotranspiration-groundwater level regulation under agriculture. Close to the deepest (20 m) and most active incisions, groundwater level and greenness declined and stream baseflow showed no seasonal fluctuations, hinting decoupling from evapotranspiration. Intense ecological and geomorphological transformations in this catchment exposed the interplay of five mechanisms governing evapotranspiration/streamflow partition including (a) unsaturated uptake and both (b) riparian and (c) distributed uptake from the saturated zone by plants, as well as (d) deepening incisions and (e) sediment deposits over riparian zones by streams. Acknowledging the complex interplay of these mechanisms with groundwater is crucial to predict and manage future hydrological changes in the dry plains of South America. 相似文献
The Mio-Pliocene aquifer of the coastal sedimentary basin of Benin is the most exploited aquifer for water supply to the urbanised region in the southern part of the country. The population explosion is putting increasing pressure on quantitative and qualitative aspects of the groundwater resources. Preventing groundwater contamination caused by surface waters requires a thorough understanding of surface-water/groundwater interactions, especially the interactions between the Mio-Pliocene aquifer and surface waters. This study aimed to investigate the interactions between groundwater and surface waters along the major rivers (Sô River and Ouémé Stream) and brooks in the Ouémé Delta. Field campaigns identified 75 springs located in the valleys which feed the rivers, and thus maintain their base flow. The piezometric results indicated, through flow direction assessment, that the Mio-Pliocene aquifer feeds Ouémé Stream and Sô River. Chemical analyses of groundwater and surface waters show similar chemical facies, and changes in the chemical composition in groundwater are also observed in the surface waters. Moreover, the isotopic signatures of surface waters are similar to those of the groundwater and springs, which led to the identification of potential groundwater discharge areas. As a result of groundwater discharge into surface waters, the fraction of groundwater in the surface water is more than 66% in the brooks, regardless of the season. In the Ouémé Stream and Sô River, the fraction of groundwater is 0–21% between June and September, while from October to March it is 47–100%.
Climatic Change - Carbon dioxide removal (CDR) describes a suite of controversial approaches to mitigating climate change that involve removing existing carbon dioxide from the atmosphere. Through... 相似文献
Editors' Note: The following is the tenth in the Singapore Journal of Tropical Geography Lecture Series. It is based on the plenary presentation of 13 April at the AAG held in Seattle in 2011. In this essay I explore relational poverty analysis to take seriously the spatially varied intersections of political‐economic, social ordering and cultural‐political processes in shaping understandings of poverty. My work as part of the Middle Class Poverty Politics Research Group employs a relational comparative methodology to theorize where, when and under what circumstances those framed as ‘middle class’ act in opposition to or in solidarity with those named as ‘poor’. Our approach focuses on the exploitative effects of capital accumulation, processes of unequal sociospatial categorization and political and discursive systems that limit or exclude the poor. Our research focuses on places experiencing capitalist crisis because intense periods of restructuring highlight material and discursive struggles over poverty. We conclude by identifying a research agenda focused on the ways in which poverty politics are constituted by the nonpoor through place and in the articulation of places with processes of political economy, governance and cultural politics. 相似文献