Crustal and upper mantle S-wave velocity structure beneath the Bransfield Strait (West Antarctica) from regional surface wave tomography

Regional surface wave tomography in the sub-Antarctic Scotia Sea is helpful in revealing the nature of the crust and the S-wave seismic velocity profile beneath the Bransfield Strait. The joint use of our regional network, global seismographic network stations and local temporary arrays provide better lateral resolution than that obtained in our previous studies concerning the Scotia Sea region.Tomographic analysis of data obtained using 10 broad band seismic stations and more than 300 regional events, shows that the Bransfield Basin is characterised by a strong group velocity reduction of 8% with respect to the surrounding areas, in the period range from 15 s to 50 s.The crustal and upper mantle models of the eastern, central and western Bransfield Basin are obtained by joint inversion of Rayleigh and Love local dispersion curves from 15 s to 50 s. In addition our data set is expanded to a broader period interval (1–80 s), in central Bransfield Strait in order to better constrain the upper mantle and shallow crust.The main results can be summarized as follows: (a) the crust thins distinctly from W toward E; the variation is consistent with the type of volcanism, earthquake distribution and bathymetric observations, (b) low upper mantle velocities (soft lid) extend down to depths exceeding 70 km as a consequence of elevated temperatures, (c) the crust beneath the central Bransfield Basin displays continental characteristics with a gradually increasing S-wave velocity distribution versus depth analogous to the East African Rift structure of Kenya, (d) negative velocity gradients are present in the lower crust beneath the eastern Bransfield Basin; these could be interpreted as magmatic bodies originating from decompression melting of the mantle.     

Analytical and numerical analysis of pressure drawdown in a poroelastic reservoir with complete overburden effect considered

Starting from an analytical reservoir model that incorporates full interaction with an elastic overburden, a new hybrid mathematical approach is developed by combining two numerical discretization methods. A tabular reservoir (petroleum reservoir or an aquifer) in an infinite or semi-infinite domain is viewed as a macroscopic displacement discontinuity, allowing use of the efficient displacement discontinuity mathematical method to calculate stresses and displacements that arise because of pressure changes. A 3-D finite element method using a poroelastic formulation is used to discretize the reservoir itself. By coupling the displacement discontinuity and finite element methods, a 3-D large-scale poroelastic reservoir can be simulated within an infinite or semi-infinite domain. The numerical model has been verified through comparison to known solutions, and some time-dependent pressure drawdown problems are analyzed. Results indicate that including the complete overburden (reservoir surroundings) response has a significant effect on pressure drawdown in a poroelastic reservoir during pumping, and should be incorporated in appropriate applications such as well test equations and subsidence analyses.     

Mechanical response of the south flank of kilauea volcano, hawaii, to intrusive events along the rift systems

Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany rift intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual rift intrusions is immediate; the increased rate of earthquake activity lasts from 1 to 4 weeks. Horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest rift intrusion, however, results in a slight extension of the subaerial portion of the south flank.Horizontal strain measurements along the south flank are used to locate the January 1983 east-rift intrusion, which resulted in eruptive activity. The intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet. This model suggests that the intrusive body that compressed the south flank in January 1983 extended from the surface to about 2.4 km depth, and was aligned along a strike of N66°E. The intrusion is approximately 11 km in length, extended beyond the January 1983 eruptive fissures, which are 8 km in length and is contained within the 14-km-long region of shallow rift earthquakes.     

Correlation of gravity with the Maquereau Group, southern Gaspe Peninsula, Quebec

Gravity observations at 150 locations in the Port-Daniel and Chandler area, southeastern Gaspé, Quebec, delineate an E-W to ENE-WSW trending elliptical positive Bouguer gravity anomaly with an amplitude of 19 mGal and a residual gravity anomaly of circa 22 mGal. This anomaly correlates closely with the Lower Cambrian and/or Hadrynian Maquereau Group, the steep gradients defining it coinciding with the contact between the group and the surrounding Ordovician and Siluro-Devonian sedimentary rocks. On the basis of its similar geological setting, this gravity anomaly may be compared with the positive Bouguer anomalies observed over the Fleur de, Lys zone to the east of the Baie Verte lineament in Newfoundland. Tridimensional modelling of the gravity data is inconsistent with a serpentinite dome as originally proposed and it suggests that the Maquereau Group represents an upthrusted slice of deep-seated volcanosedimentary sequences. These were originally located on the lower segment of the continental slope; they constituted a topographic high during the final process of the mountain building at the Taconic phase (Middle to Upper Ordovician time). The most probable way of emplacement of the Maquereau block is through a tear-fault running E-W to ESE-WNW in the southern Gulf of St. Lawrence west of Cape Breton and resulting from Early Paleozoic continental collision between a Eurafrican continent and a North American continent which had a salient located beneath the site of the modern Gulf. The Maquereau may then have been reactivated with a left-lateral motion accompanied of a rotation about a sub-horizontal axis. The presumed Baie Verte-Brompton line ought to be displaced to the north and the Humber zone is narrowed.     

A simple method of computing the variation of annual precipitation over mountainous terrain

A method for computing the distribution of annual precipitation for mountainous areas is presented. As a pilot study, the South Thompson River basin in British Columbia is examined. In addition to data from climatological (valley) stations, annual precipitation is estimated for snow course (mountain) locations from the water equivalent of the snowpack on April 1.An equation for the dependence of precipitation amount on orography is derived from simple physical considerations. Regression equations based on this are then computed and the calculated precipitation is checked with runoff data. A basic predictor is the mean vertical water vapor transport through a horizontal unit area due to flow over undulating terrain. This depends on the average slope of a region 3 deg long by 2 deg lat centered on each grid point. The transport at the earth's surface has a simple correlation coefficient with the combined valley and mountain precipitation data of 0.76. When the transport is computed at the mean cloud base (taken as 1800 m above sea-level), the correlation coefficient rises to 0.87.     

Influence de la subsidence sur la sédimentation

Résumé Des seuils peu profonds et stables, balayés par des courants (stabiliseuils) séparaient en France pendant le Jurassique supérieur des aires subsidentes où s'accumulaient les sédiments; des récifs coralliens pouvaient s'y développer lorsque la subsidence était comprise entre 30 et 70 m. par zone paléontologique, et constituer alors de véritables barrières: la localisation des régions où la subsidence optima était réalisée est par conséquent un élément essentiel de l'abondance et de la répartition des sédiments calcaires.Les variations locales de la subsidence constituent donc un facteur important de la sédimentation, non seulement au point de vue quantitatif, mais encore en ce qui concerne la nature des dépôts.     

Geophysics of the Quebec Appalachians

This paper deals with a synthesis of the geophysics of the Quebec Appalachians. An emphasis is given to the regional geophysical surveys for the final geological interpretation. Regional, residual and downward continued aeromagnetic (AM) data yield information on the tectonic history of the region. The main features are pattern recognition of folded and particularly faulted structures and the boundaries of the tectonic domains. Three main fault systems have been identified and classified using AM information. In addition, depths to the crystallise basement and to the Cambro-Ordovician magnetic layers were obtained for sectors of the Gulf of St. Lawrence-Gaspé region. Nine main geological features are extracted from the processed AM data. Detailed geological modelling of some of the identified structures (e.g. nappes) are presented.Five main geological features are recognized from the gravity data. These features are correlated with the ones obtained from AM data whenever possible. Geological models based on information from surface geology, rock density contrasts and occasional contraints from regional seismic reflection data are presented. The boomerang shape of the Sutton-Bennett anticlinorium and the planar or curved slab-like shape of the obducted ophiolite bodies (upper mantle proto-oceanic floor) may be considered as the significant features.Regional reflection seismic data give a clear geological picture of three (out of four) distinguishable zones of the Quebec Appalachians, that is: autochthonous, parautochthonous, and transition zone: parautochthonous-allochthonous(corresponding approximately to the external domain). The pattern recognition of the allochthonous (approximate internal domain) is somewhat more difficult to decipher from the reflection seismic data. Intraplate seismicity and seismotectonics indicate the presence of four zones of high seismicity in southern Quebec. In almost all zones, the seismotectonic history goes back to Late Precambrian (Hadrynian) times.The scarce and scattered paleomagnetic data of geological formations located on the platform and the external domain of the Quebec Appalachians and in the internal domain are compared with those belonging to the stable North American plate. The paleomagnetic results indicate that the angular difference between the poles from the platform and external domain is large at Cambrian times (40°) and small at Devonian times (5°-10°). This suggests a fast rate of motion and accretion of the internal domain relative to the North American Plate in the Cambrian—Lower Devonian time span (550→-385 Ma).     

Ecological aspects of fin whale and humpback whale distribution during summer in the Norwegian Sea

The Norwegian Sea is a migration and feeding ground for fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in summer. During the last decade, significant structural changes in the prey community, including northerly expansion and movement in the distribution of pelagic fish species, have been reported from this ecosystem. However, little information on whale feeding ecology exists in the Norwegian Sea and surrounding waters. A total of 59 fin whales and 48 humpback whales were sighted during 864 h of observation over an observation distance of about 8200 nmi (15,200 km) in the Norwegian Sea from 15 July to 6 August 2006 and 2007. The fin whale group size, as mean (±SD), varied between one and five individuals (2.1 ± 1.2 ind.) and humpback whale group size varied between one and six individuals (2.5 ± 1.7 ind.). Fin‐ and humpback whales were observed mainly in the northern part of the study area, and were only found correlated with the presence of macro‐zooplankton in cold Arctic water. Humpback whales were not correlated with the occurrence of adult Norwegian spring‐spawning herring (Clupea harengus) except for the northernmost areas. Despite changes in the whale prey communities in the Norwegian Sea, no apparent changes in fin‐ or humpback whale distribution pattern could be found in our study compared to their observed summer distribution 10–15 years ago.     

Environmental public health applications using remotely sensed data

We describe a remote sensing and geographic information system (GIS)-based study that has three objectives: (1) characterize fine particulate matter (PM_2.5), insolation and land surface temperature (LST) using NASA satellite observations, Environmental Protection Agency (EPA) ground-level monitor data and North American Land Data Assimilation System (NLDAS) data products on a national scale; (2) link these data with public health data from the REasons for Geographic And Racial Differences in Stroke (REGARDS) national cohort study to determine whether these environmental risk factors are related to cognitive decline, stroke and other health outcomes and (3) disseminate the environmental datasets and public health linkage analyses to end users for decision-making through the Centers for Disease Control and Prevention (CDC) Wide-ranging Online Data for Epidemiologic Research (WONDER) system. This study directly addresses a public health focus of the NASA Applied Sciences Program, utilization of Earth Sciences products, by addressing issues of environmental health to enhance public health decision-making.     

Market penetration metrics: tools for additionality assessment?

Abstract

Project-based emission reduction or ‘offset’ programs are being implemented widely, from the CDM (Clean Development Mechanism) to corporate voluntary efforts and municipal and state-level activities. Additionality assessment remains a central and persistent challenge in all programs. Concerns have been raised with methods currently used, such as investment analysis, barrier analysis, and performance thresholds. They have been variously critiqued for high costs, resistance to standardization, weak environmental integrity, and susceptibility to gaming. Technology penetration rates provide another means to infer additionality, and could be a potentially useful complement to other methods. The notion is that emerging technologies with low but increasing penetration rates typically require some type of support, as might be provided through offsets markets, to compete effectively in the marketplace. For penetration rate analysis to provide a useful tool for additionality assessment, several fundamental questions need to be addressed. What do penetration rates represent and how can they be measured? How can additionality evaluation utilize penetration rates? For which sectors and project types are the use of penetration rates most promising? This article shows that penetration tests have a mixture of pluses and minuses, with greater relevance in certain market niches and regions. Reasonable ranges for penetration thresholds are discussed, along with partial crediting approaches to reduce ‘knife-edge’ effects.