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21.
We use a simple approach to estimate the present-day thermal regime along the northwestern part of the Western Indian Passive Margin, offshore Pakistan. A compilation of bottom borehole temperatures and geothermal gradients derived from new observations of bottom-simulating reflections (BSRs) allows us to constrain the relationship between the thermal regime and the known tectonic and sedimentary framework along this margin. Effects of basin and crustal structure on the estimation of thermal gradients and heat flow are discussed. A hydrate system is located within the sedimentary deep marine setting and compared to other provinces on other continental margins. We calculate the potential radiogenic contribution to the surface heat flow along a profile across the margin. Measurements across the continental shelf show intermediate thermal gradients of 38–44 °C/km. The onshore Indus Basin shows a lower range of values spanning 18–31 °C/km. The Indus Fan slope and continental rise show an increasing gradient from 37 to 55 °C/km, with higher values associated with the thick depocenter. The gradient drops to 33 °C/km along the Somnath Ridge, which is a syn-rift volcanic construct located in a landward position relative to the latest spreading center around the Cretaceous–Paleogene transition. 相似文献
22.
Prawn postlarvae fishing in coastal Bangladesh: Challenges for sustainable livelihoods 总被引:1,自引:0,他引:1
Fishing for prawn (Macrobrachium rosenbergii) postlarvae is a major contributor to the livelihoods of the coastal poor in Bangladesh, including women. A study of coastal livelihoods along the lower Pasur River in southwest Bangladesh indicates that on average 40% of total annual income comes from postlarvae fishing during the few months involved. However, indiscriminate fishing of wild postlarvae, with high levels of by-catch, has an impact on biodiversity in coastal ecosystems. This has provoked imposition of restrictions on postlarvae collection. The ban has, however, not been firmly enforced because of the lack of alternative livelihoods for coastal poor. A conceptual framework, drawn from an approach to poverty reduction known as the sustainable livelihoods approach, is applied to understanding the role of prawn postlarvae fishing. Evidence from this study suggests that postlarvae fishers faced a number of livelihood constraints, including poor livelihood assets. This paper concludes that wider livelihood options need to be found for postlarvae fishers to support their livelihoods. 相似文献
23.
Biased estimation: a simple framework for inversion and uncertainty analysis with prior information 总被引:1,自引:0,他引:1
Max A. Meju 《Geophysical Journal International》1994,119(2):521-528
24.
Barbara B. Prézelin Max M. Tilzer Oscar Schofield Clivia Haese 《Aquatic Sciences - Research Across Boundaries》1991,53(2-3):136-186
This tutorial was designed for nonbiologists requiring an introduction to the nature and general timescales of phytoplankton responses to physical forcing in aquatic environments. As such, an effort was made to highlight biological markers which might assist in identifying, measuring and/or validating physical processes controlling the variability in the distribution, abundance, composition and activity of phytoplankton communities. Given the recent advances in environmental optics and remote sensing capabilities, a special emphasis was placed on the nature and utility of phytoplankton optical properties in current bio-optical modelling efforts to predict temporal and spatial variability in phytoplankton productivity and growth. 相似文献
25.
David J. Schwab 《Dynamics of Atmospheres and Oceans》1982,6(4):251-278
The hydrodynamic equations governing the water-level response of a lake to wind stress are inverted to determine wind stress from water-level fluctuations. In order to obtain a unique solution, the wind-stress field is represented in terms of a finite number of spatially dependent basis functions with time-dependent coefficients. The discretized version of the inverse equation is solved by a least-squares procedure to obtain the coefficients, and thereby the stress. The method is tested for several ideal cases with Lake Erie topography. Real water-level data is then used to determine hourly values of vector wind stress over Lake Erie for the period 5 May–31 October, 1979. Results are compared with measurements of wind speed and direction from buoys deployed in the lake. Calculated stress direction agrees with observed wind direction for wind speeds > 7.5 m s−1. Under neutral conditions, calculated drag coefficients increase with the wind speed from 1.53 × 10−3 for 7.5−10 m s−1 winds to 2.04 × 10−3 for 15−17.5 m s−1 winds. Drag coefficients are lower for stable conditions and higher for unstable conditions. 相似文献
26.
This synthesis of detailed geological and geophysical information relates deep crustal structure to deformation and the emplacement of granites in the South Armorican Massif and the adjacent continental shelf. Near the continental margin a zone of geophysical anomalies is regarded as a nearly complete line of suture between a southern continent and America. A major mafic body in the trace of the supposed suture in interpreted as a relic of probable oceanic crust which has apparently acted as a deflector of regional strain.It is proposed that late in the Hercynian collision history, during late Carboniferous time, compressional strain acted across the mafic body and can be directly related to generation of younger regional structures in the metasediments and to localization of granite emplacement. 相似文献
27.
The arrival time difference for the AB branch of PKP from deep Tonga earthquakes is constant over years with a standard deviation
of ±0.05 seconds at seismographs located 10 to 50 km from each other. If published travel time curves are used to calculate
the relative residuals of PKP the standard deviation from the constant mean is improved by approximately 0.01 seconds for
AB branch data. For the BC branch, standard deviations of relative travel times of ±0.06 seconds are reduced to less than
±0.05 seconds by calculating relative residuals. We conclude that changes of crustal transit time forP-waves could be resolved, based on careful PKP arrival time measurement at two or more neighboring stations if the changes
exceed 0.05 sec and last for more than one year. The conditions for achieving this result are that PKP from Tonga earthquakes
is clearly recorded, and that time-keeping is accurate. The data on which these conclusions are based were obtained from the
Graefenberg seismograph array, which is located in West Gemany and consists of 13 stations separated by distances of 10 km
to 100 km. We propose that relative arrival times of PKP from Tonga could be used in the Mediterranean - Middle East area
to search for precursory travel time changes before large earthquakes. 相似文献
28.
Measurement of 17 laboratories on the stable isotope reference materials, NBS 22 lubricating oil and NBS 21 graphite, resulted in a revised calibration on the PDB scale. NBS 22 13C/12C ratios of all laboratories did not demonstrate a gausssian distribution. Therefore, values which resulted from direct comparison with NBS 20 carbonate standards were selected the mean value of which is ; this value is recommended as new value for NBS 22. The reported variations in δ13C for NBS 21 were consistent within the accuracies for single meaurements; the mean value is ?28.16 ± 0.01. The variations of D/H ratios of NBS 22 also were consistent with the accuracy quoted, with a mean value of ?119?. 相似文献
29.
Comment on 'The magnetotelluric phase tensor' by T. Grant Caldwell, Hugh M. Bibby and Colin Brown 总被引:1,自引:0,他引:1
Max Moorkamp 《Geophysical Journal International》2007,171(2):565-566
We demonstrate a minor inconsistency in the appendix of 'The magnetotelluric phase tensor' by Caldwell et al. that can lead to incorrect results, and provide a simple solution for this problem. 相似文献
30.