Management of the UK mackerel fisheries: An economic perspective     

David J. Whitmarsh  James A. Young 《Marine Policy》1985,9(3):220-236

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Pop-up bottom seismic recorder (PUBS) of the Institute of Oceanographic Sciences,U.K.     

J. J. Langford  R. B. Whitmarsh 《Marine Geophysical Researches》1977,3(1):43-63

A pop-up bottom seismic recorder designed for seismic refraction experiments was built by the Institute of Oceanographic Sciences in 1968. The device is housed within a 71 cm diameter sphere weighing 270 kg when launched. signals picked up by a hydrophone are recorded in analogue form on magnetic tape in the band 2–100 Hz. The total continuous recording period is 12 hr but the lifetime of the system can be effectively extended by cycling the tape-recorders to allow shooting to go on for up to 3 days. Ballast release is by acoustic command or by pre-set clock. The instruments have been used in water depths from 150 to 4820 m making a total of 63 deployments with a 95% recovery rate. A new version with three-component geophones is being built.  相似文献   

Fishing effort and fisheries policy     

S. Cunningham  D. Whitmarsh 《Marine Policy》1980,4(4):309-316

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A technique for conducting seismic refraction experiments on the ocean bed using bottom shots     

R. E. Kirk  K. Robertson  R. B. Whitmarsh  P. R. Miles 《Marine Geophysical Researches》1991,13(2):153-160

A technique has been devised for firing arrays of bottom shots on the ocean bed in depths upto 4000 m or more. Ten kilogram explosive charges are dropped from the surface while the shooting ship is navigated acoustically. They are detonated at preset times by an electronic timer which initiates an electrical detonator, detonating cord and cast PETN/TNT explosive. Ranges to ocean bottom seismographs, and the shot instants, can be calculated from the arrival-time differences of the direct and surface-reflected water waves. The accuracy, which is dependent on water-depth and range, was better than 22 m in range and 14 msec in shot instant for our experiments.  相似文献   

Ccte d'Ivoire-Ghana margin: seismic imaging of passive rifted crust adjacent to a transform continental margin     

C. Peirce  R. B. Whitmarsh  R. A. Scrutton  B. Pontoise  F. Sage  J. Mascle 《Geophysical Journal International》1996,125(3):781-795

During May 1990 and January-February 1991, an extensive geophysical data set was collected over the Côte d'Ivoire-Ghana continental margin, located along the equatorial coast of West Africa. The Ghana margin is a transform continental margin running subparallel to the Romanche Fracture Zone and its associated marginal ridge—the Côte d'Ivoire-Ghana Ridge. From this data set, an explosive refraction line running ∼ 150 km, ENE-WSW between 3°55'N, 3°21'W and 4°23'N, 2°4'W, has been modelled together with wide-angle airgun profiles, and seismic reflection and gravity data. This study is centred on the Côte d'Ivoire Basin located just to the north of the Côte d'Ivoire-Ghana Ridge, where bathymetric data suggest that a component of normal rifting occurred, rather than the transform motion observed along the majority of the equatorial West African margin.
Traveltime and amplitude modelling of the ocean-bottom seismometer data shows that the continental Moho beneath the margin rises in an oceanward direction, from ∼ 24 km below sea level to ∼ 17 km. In the centre of the line where the crust thins most rapidly, there exists a region of anomalously high velocity at the base of the crust, reaching some 8 km in thickness. This higher-velocity region is thought to represent an area of localized underplating related to rifting. Modelling of marine gravity data, collected coincident with the seismic line, has been used to test the best-fitting seismic model. This modelling has shown that the observed free-air anomaly is dominated by the effects of crustal thickness, and that a region of higher density is required at the base of the crust to fit the observed data. This higher-density region is consistent in size and location with the high velocities required to fit the seismic data.  相似文献   

Journeys to the street: the complex migration geographies of Ugandan street children     

Lorraine Young 《Geoforum》2004,35(4):471-488

Children have generally been afforded little attention in migration research or unsatisfactorily included within family migration. Although they are an important consideration in family decisions to move, children also engage in autonomous, independent migration. Further, researchers now argue for the need to situate migration within political, economic and social conditions to obtain a full understanding of why people migrate. Through the use of children-centred research methods, and in-depth interviews with key informants, this paper considers children's journeys to the street in Uganda. By integrating an analysis of Ugandan street children's spatial origins with the familial and societal contexts of their migration decisions, this research highlights the complexity of their migration. In addition, an exploration of the impact of changing social, spatial and temporal conditions on street children's movements illustrates that their journeys are far more than just single processes.  相似文献   

An investigation of seismic anisotropy due to cracks in the upper oceanic crust at 45°N, Mid-Atlantic Ridge     

R. S. White  R. B. Whitmarsh 《Geophysical Journal International》1984,79(2):439-467

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Seismic refraction studies of the upper igneous crust in the North Atlantic and porosity estimates for Layer 2     

R.B. Whitmarsh 《Earth and Planetary Science Letters》1978,37(3):451-464

A number of unreversed refraction profiles up to 40 km long and with closely spaced shots has been interpreted to provide the structure of oceanic Layer 2. Different velocity/depth models based on a homogeneous layered structure and on a gradient structure have been obtained for each profile. The gradient models are believed to be a better representation of the real earth. They are all remarkably similar with a predominant velocity gradient of 0.85–1.35 km s^?1 km^?1 ending with a slowly downward increasing velocity of about 6 km s^?1 at about 2 km depth. The positive gradient can be reasonably explained by the reduction downwards of bulk porosity, particularly due to the closure of cracks, in a simple two-component, basalt plus voids, model. The model takes account of weathering but not of metamorphism. A theory, based on oversimplified assumptions about the rocks in Layer 2, allows rough estimates of porosity at different depths to be made.  相似文献   

Seismic structure of a seaward-dipping reflector sequence southwest of Rockall Plateau     

R. B. Whitmarsh  P. R. Miles 《Geophysical Journal International》1987,90(3):731-739

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Visco-damage tension model for rocks in ground-shock applications     

Lorraine Whitman 《国际地质力学数值与分析法杂志》1985,9(1):71-89

A simple rate-dependent tension model, tailored primarily for rocks in ground-shock calculations, has been constructed. It is formulated as an internal state variable theory with spherical void development taken to approximate the underlying dissipative micromechanism. This simplifying assumption of ductile, rather than brittle, damage growth has been made to enhance the practicality of the model for large-scale problems. The model has been restated within the fromework of (strain-softening) viscoplastcity to associate it with the desirable mathematical properties of the latter theory. The tension option, extended to include healing in the post-damage compressive phase, has been implemented in a standard cap constitutive routine and is referred to as the visco-damage tension model. Model parameters are selected for a shale-like material. Results of uniaxial shock-loading strain-rate calculations exhibit desired characteristics in tension. Damage-related hysteretic effects are illustrated through cyclic loading calculations. It is planned to develop more effecient computational procedures to facilitate adoption of the model into large-scale ground shock calculations. Anisotropic extensions of the model will then be considered.  相似文献