Displacement and strain patterns from naturally occurring shear zone terminations

Strain distribution patterns are described from several naturally occurring ductile shear zone terminations and a two-fold classification is suggested. Type I termination patterns show a symmetrical decrease in strain area and intensity, and are associated with very low shear strain (ψ) values in the main shear zone. The more common Type II termination patterns show a symmetrical increase in strain area with decrease in strain intensity. Some brittle-ductile examples of Type II terminations contain secondary shears that resemble splay faults. All the available evidence suggests that the deformation near the terminations of these shear zones is not plane strain, nor do the observed strain patterns readily fit the existing theoretical models.     

The formation of deep topsoils in Orkney

The Soil Survey for Scotland, in their mapping of the soils in Orkney, identified a deep top phase of the Bilbster Series. This soil is distinguished by having a topsoil usually in excess of 75 cm and it occurs almost exclusively on the Mainland of Orkney, especially in the west round Marwick and Skaill Bays. An anthropogenic origin to this soil is proposed and the present study is designed to investigate the particular processes of formation which have led to the increase in soil depth. Results from transect and grid surveys indicate how the soil is thickest adjacent to old farms. The historical literature suggests a wide range of possible inputs from seaweed and calcareous sand to turves after they had been used as bedding for cattle. Analytical results support the last process as the dominant one and an accumulation rate of c.1 mm/yr is proposed.     

Uptake and loss of zinc and lead by mussels (Mytilus edulis) and relationships with body weight and reproductive cycle

The uptake and loss of zinc and lead from the whole soft parts of the mussel Mytilus edulis were investigated under natural conditions in north-east England. Mussels in which high concentrations of these metals were found were transferred to an area where low concentrations were found, and vice versa. Mussels from both areas were also kept in tanks and periodic measurements of metal contents were made. Indications of uptake and loss were greatly affected by changing body weights and the work suggests that phase of reproductive cycle (for animals in the environment) and condition (for animals in tanks) have to be closely considered when reporting on levels of metals in mussels, especially in terms of concentration.     

On the interaction of rayleigh surface waves with structures

A two-dimensional soil-structure interaction analysis is carried out for transient Rayleigh surface waves that are incident on a structure. The structure is modelled by a three-degree of freedom rigid basemat to which is attached a flexible superstructure, modelled by a single mass-spring system. The structural responses to a given Rayleigh wave train are compared with those that would have been obtained if the free-field acceleration-time history had been applied as a normally incident body wave. The results clearly exhibit the [frequency filtering] effects of the rigid basemat on the incident Rayleigh waves. It is shown that, if seismic excitation of a structure is, in fact, due to Rayleigh surface waves, then an analysis assuming normally incident body waves can considerably over-estimate structural response, both at basemat level for horizontal and vertical motions and for vertical oscillations of the superstructure. However, in the examples considered here, relatively large rocking effects were induced by the Rayleigh waves, thus giving maximum horizontal accelerations in the superstructure that were of comparable magnitude for Rayleigh and normally incident body waves.     

Periodic frontogenesis in a region of freshwater influence

Observations are presented from a series of three conductivity-temperature-depth (CTD) surveys of the salinity and temperature structure of Liverpool Bay, a region that is strongly influenced by the input of fresh water from the rivers of northwest England. The surveys demonstrate the development, seaward movement, and eventual decay of a haline front. The frontogenesis is driven by the relaxation of a freshwater-induced horizontal density gradient following the decrease in tidal range at neap tides. It results in the area of Liverpool Bay being stratified for a period of 8 d before the increase in tidal mixing as the spring tide approaches returns the region to its initial vertically mixed state. In Liverpool Bay this process usually repeats on the spring-neap cycle, though strong wind-mixing may prevent the frontogenesis and subsequent stratification. Analysis with a 1-dimensional numerical model suggests that relaxation of an initially nonlinear horizontal density field, creating the front, is triggered by the stability produced by tidal straining of the water column during the ebb half-cycle. The reduction in tidal mixing energy approaching neap tide does not lead to frontogenesis without this initial stability. Such a regular stratification signal will have a marked effect on the local environment. The periodic frontogenesis will act as a tidal pump, moving buoyant substances in the water column offshore, while the onshore residual currents lower in the water column will more deeper dissolved substances inshore. The cycling of stability on the springneap time scale is considerably faster than the seasonal cycle of thermal stratification in the shelf seas, but is similar in creating the conditions required for phytoplankton blooms. Conditions favorable for enhanced primary production may therefore occur frequently in such regions of freshwater influence.     

Sediment-derived chronologies of persistent contaminants in Jamaica Bay,New York

Chronologies of particle-associated contaminant levels were developed for Jamaica Bay, an embayment of the Atlantic Ocean on southwestern Long Island. A major potential source of contaminants to the system is wastewater discharge, which comprises most of the freshwater input to the bay. Sediment core sections were analyzed for Cs-137, Pu-239, 240, and Be-7 activities which were then used to establish net particle accumulation rates. Samples deposited from the early 1950s through the late 1980s were analyzed for metals and chlorinated hydrocarbon contaminants. Trace metals, including copper, lead, chromium, zinc, and mercury, were elevated to levels several times those of pre-industrial concentrations. These metals decreased by about 50% between the mid 1960s and the late 1980s. Chlorinated hydrocarbon concentrations, including polychlorinated biphenyls, chlordane, and dichlorodiphenyltrichloroethane-derived compounds, decreased by a factor of five to ten between the late 1960s and the late 1980s. Local improvements in wastewater treatment and national efforts to regulate the uses and releases of specific chemicals are the most likely explanation of declines in contaminant levels in these sediments.