Characteristic features of the occurrence of gas-fluid emanations on the northeastern slope of Sakhalin Island, Sea of Okhotsk

This paper summarizes the results of combined studies in the areas of the occurrence of gas-fluid emanations in the water column, on the seafloor, and in the upper part of the sedimentary section on the northeastern slope of Sakhalin Island (Sea of Okhotsk). The phenomena typical of methane seeps were characterized in detail: the presence of acoustic anomalies, high concentrations of methane in the water and sediments, and the specific features of the sedimentary section (the textural and structural features, the character of the mineral inclusions and gas hydrates, and the chemical composition). The component composition of the gases (including the accompanying gas hydrates), which is almost free of heavy hydrocarbon homologues of methane; the light carbon isotopic compositions of the methane and carbonate concretions; and the low temperatures of the near-bottom water and sediments suggest that the occurrence of numerous methane emanations is related to gas generation in the upper part of the sedimentary sequence. No evidence was found for the existence of a deep center of gas formation within the seafloor area considered. Typical submarine mud volcanic edifices were also not found.     

Geochronology and geochemistry of Grenvillian igneous suites in the northern Oaxacan Complex, southern Mexico: tectonic implications

Chemical and U–Pb isotopic analyses of metaigneous rocks in the northern Oaxacan Complex in southern Mexico indicate that they form part of two granitic–gabbroic suites intruded at 1157–1130 and 1012 Ma, which were metamorphosed under granulite facies conditions between 1004 and 980 Ma. Although the older suite has both within-plate and arc geochemical signatures, the arc characteristics (enrichment of La and Ce relative to Nb, Ta, and Th) are inferred to result from crustal contamination, a conclusion consistent with their negative _Nd signatures. The younger suite is spatially associated with anorthosites (from which we were unable to acquire a protolith age), suggesting that collectively it forms part of anorthosite–mangerite–charnockite–granite (AMCG) suites. The tholeiitic nature of the mafic rocks along with the within-plate character of the felsic rocks suggests that they were intruded during extension related to either farfield backarc rifting, rifting above a slab window, or anorogenic intercontinental rifting. Potentially correlative AMCG suites are widespread in Mexico, the Grenville Province of eastern Canada and northeastern USA, and the Andean massifs of Colombia, however, Pb isotopic data most closely resemble those in South America. These data are consistent with published hypotheses that suggest Oaxaquia represents an exotic terrane derived from Amazonia.     

Marine risk assessment: linear alkylbenzenesulponates (LAS) in the North Sea

The fate of linear alkylbenzenesulponates (LAS) in estuaries and coastal areas of the North Sea has been characterized with simple environmental models. The predicted concentration range in the estuaries around the North Sea (0.9-9 microg LAS l(-1)) was validated by monitoring data (1-9 microg LAS l(-1)). In offshore sites of the North Sea, it is estimated--and experimentally verified for a few sites--that the LAS concentration is below analytical detection limit (i.e., 0.5 microg LAS l(-1)). The effects of LAS on marine organisms have been reviewed. For short-term acute tests, there was no significant difference (p = 0.83) between the mean LC50 values of freshwater and marine organisms (mainly pelagic species tested, 4.1 and 4.3 mg LAS l(-1), respectively). For longer-term chronic tests, it appeared that the sensitivity (mean no-observed effect concentration (NOEC) value) of marine and freshwater organisms (0.3 and 2.3 mg LAS l(-1), respectively) was significantly different pt-test = 0.007). The predicted no-effect-concentrations (PNEC) were 360 and 31 microg LAS l(-1), for freshwater and marine pelagic communities, respectively. Given that the maximum expected estuarine and marine concentrations are 3 to > 30 times lower than the PNEC, the risk of LAS to pelagic organisms in these environments is judged to be low.     

Towards a direct collapse–load method of design for concrete frames subjected to severe ground motions

Most current methods of design for concrete structures under earthquake loads rely on highly idealized ‘equivalent’ static representations of the seismic loads and linear‐elastic methods of structural analysis. With the continuing development of non‐linear methods of dynamic analysis for the overload behaviour and collapse of complete concrete structures, a more direct and more accurate design procedure becomes possible which considers conditions at system collapse. This paper describes an evaluation procedure that uses non‐linear dynamic collapse–load analysis together with global safety coefficients. A back‐calibration procedure for evaluating the global safety coefficients is also described. The aim of this paper is to open up discussion of alternative methods of design with improved accuracy which are necessary to move towards a direct collapse–load method of design. Copyright © 2002 John Wiley & Sons, Ltd.     

A determination of source properties of large intraplate earthquakes in Alaska

Historically, large and potentially hazardous earthquakes have occurred within the interior of Alaska. However, most have not been adequately studied using modern methods of waveform modeling. The 22 July 1937, 16 October 1947, and 7 April 1958 earthquakes are three of the largest events known to have occurred within central Alaska (M _s =7.3,M _s =7.2 andM _s =7.3, respectively). We analyzed teleseismic body waves to gain information about the focal parameters of these events. In order to deconvolve the source time functions from teleseismic records, we first attempted to improve upon the published focal mechanisms for each event. Synthetic seismograms were computed for different source parameters, using the reflectivity method. A search was completed which compared the hand-digitized data with a suite of synthetic traces covering the complete parameter space of strike, dip, and slip direction. In this way, the focal mechanism showing the maximum correlation between the observed and calculated traces was found. Source time functions, i.e., the moment release as a function of time, were then deconvolved from teleseismic records for the three historical earthquakes, using the focal mechanisms which best fit the data. From these deconvolutions, we also recovered the depth of the events and their seismic moments. The earthquakes were all found to have a shallow foci, with depths of less than 10 km.The 1937 earthquake occurred within a northeast-southwest band of seismicity termed the Salcha seismic zone (SSZ). We confirm the previously published focal mechanism, indicating strike-slip faulting, with one focal plane parallel to the SSZ which was interpreted as the fault plane. Assuming a unilateral fault model and a reasonable rupture velocity of between 2 and 3 km/s, the 21 second rupture duration for this event indicates that all of the 65 km long SSZ may have ruptured during this event. The 1947 event, located to the south of the northwest-southeast trending Fairbanks seismic zone, was found to have a duration of about 11 seconds, thus indicating a rupture length of up to 30 km. The rupture duration of the 1958 earthquake, which occurred near the town of Huslia, approximately 400 km ENE of Fairbanks, was found to be about 9 seconds. This gives a rupture length consistent with the observed damage, an area of 16 km by 64 km.     

In-line response of a cylinder in oscillatory flow

The most widely used mathematical model to represent flow-induced in-line forces on structures is based on the Morison¹ equation. The present paper investigates the validity of using an extension of Morison's equation for non-stationary structures, by comparing predictions with results from a simple laboratory experiment. An elastically-mounted circular cylinder is placed in the sinusoidal flow of a U-tube, and responds in-line with the flow. Cylinder forces and responses are recorded over a range of Keulegan Carpenter numbers up to 35. An equation of motion is solved simply by using relative coordinates and by employing equivalent linearisation. The linear results are compared over a wide variation of parameters with solutions using the full nonlinear equation. Thereafter experimental results are compared with linear predictions.     

Detection of the old stellar component of the major Galactic bar

We present near-infrared colour–magnitude diagrams and star counts for a number of regions along the Galactic plane. It is shown that along the l =27°, b =0° line of sight there is a feature at 5.7±0.7 kpc with a density of stars at least a factor of 2 and probably more than a factor of 5 times that of the disc at the same position. This feature forms a distinct clump on an H versus J − H diagram and is seen at all longitudes from the bulge to about l =28°, but at no longitude greater than this. The distance to the feature at l =20° is about 0.5 kpc further than at l =27°, and by l =10° it has merged with, or has become, the bulge. Given that at l =27° and l =21° there is also a clustering of very young stars, the only component that can reasonably explain what is seen is a bar with half-length of around 4 kpc and a position angle of about 43°±7°.     

Estimating environmentally relevant fixed nitrogen demand in the 21st century

Human activities affect the impact of the nitrogen cycle on both the environment and climate. The rate of anthropogenic nitrogen fixation from atmospheric N₂ may serve as an indicator to the magnitude of this impact, acknowledging that relationship to be effect-dependent and non-linear. Building on the set of Representative Concentration Pathway (RCP) scenarios developed for climate change research, we estimate anthropogenic industrial nitrogen fixation throughout the 21st century. Assigning characteristic key drivers to the four underlying scenarios we arrive at nitrogen fixation rates for agricultural use of 80 to 172 Tg N/yr by 2100, which is slightly less to almost twice as much compared with the fixation rate for the year 2000. We use the following key drivers of change, varying between scenarios: population growth, consumption of animal protein, agricultural efficiency improvement and additional biofuel production. Further anthropogenic nitrogen fixation for production of materials such as explosives or plastics and from combustion are projected to remain considerably smaller than that related to agriculture. While variation among the four scenarios is considerable, our interpretation of scenarios constrains the option space: several of the factors enhancing the anthropogenic impact on the nitrogen cycle may occur concurrently, but never all of them. A scenario that is specifically targeted towards limiting greenhouse gas emissions ends up as the potentially largest contributor to nitrogen fixation, as a result of large amounts of biofuels required and the fertilizer used to produce it. Other published data on nitrogen fixation towards 2100 indicate that our high estimates based on the RCP approach are rather conservative. Even the most optimistic scenario estimates that nitrogen fixation rate will remain substantially in excess of an estimate of sustainable boundaries by 2100.     

Improved seismic hazard model with application to probabilistic seismic demand analysis

An improved seismic hazard model for use in performance‐based earthquake engineering is presented. The model is an improved approximation from the so‐called ‘power law’ model, which is linear in log–log space. The mathematics of the model and uncertainty incorporation is briefly discussed. Various means of fitting the approximation to hazard data derived from probabilistic seismic hazard analysis are discussed, including the limitations of the model. Based on these ‘exact’ hazard data for major centres in New Zealand, the parameters for the proposed model are calibrated. To illustrate the significance of the proposed model, a performance‐based assessment is conducted on a typical bridge, via probabilistic seismic demand analysis. The new hazard model is compared to the current power law relationship to illustrate its effects on the risk assessment. The propagation of epistemic uncertainty in the seismic hazard is also considered. To allow further use of the model in conceptual calculations, a semi‐analytical method is proposed to calculate the demand hazard in closed form. For the case study shown, the resulting semi‐analytical closed form solution is shown to be significantly more accurate than the analytical closed‐form solution using the power law hazard model, capturing the ‘exact’ numerical integration solution to within 7% accuracy over the entire range of exceedance rate. Copyright © 2007 John Wiley & Sons, Ltd.