On a self-consistent representation of earth models,with an application to the computing of internal flattening

Most realistic Earth models published as yet have been given in tabulated form, with the noticeable exception of three simple parametric Earth models derived by Dziewonski et al. (1975). Simple interpolation in these tables may lead to inconsistencies, when we consider certain effects which depend crucially on detailed density structure. We establish algorithmic formulae, which may be used to compute all the mechanical properties of a model in an entirely consistent way, once the density as well asP— andS— wave velocities are known. We then use this formulation to integrate Clairaut’s equation in a very efficient way, and thus obtain the hydrostatic flattening to the first order in smallness at any point inside the model. For most geodynamic purposes, we may suffice with this approximation. Finally, we show the results of some calculations of hydrostatic flattening to the first and second order, using an iterative technique of solving the integral figure equations, for an Earth model consistent with all geophysical data available at present. We find that the hydrostatic flattening at the surface should be about 1/298.8, instead of 1/296.961 as quoted by Nakiboglu (1979) for essentially the same model. Moreover, from our results, we estimate the actual flattening of the coremantle boundary to be about 1/390.3.     

Imagerie sismique de la zone de collision hercynienne dans le Sud-Est du Massif armoricain (projet Armor 2/programme Géofrance 3D)

The structure of the Hercynian collision zone in the southeast of the Armorican Massif is illustrated by a 70-km long deep seismic profile acquired in September 2000. The profile images a previously unknown south-dipping thrust that brought the Champtoceaux Domain on top of the Central Armorican Domain during Carboniferous times. Dextral strike-slip motions along the South Armorican Shear Zone, which is downward cut by the thrust zone, are partly coeval with northward thrusting. A major discontinuity, hidden by the thrust front, is also imaged in the lower crust between the Champtoceaux area and the Central Armorican Domain. These new data lead to a structural and kinematic re-interpretation of this part of the Hercynian collision zone. To cite this article: A. Bitri et al., C. R. Geoscience 335 (2003).     

Rectified flow along a vertical coastline

Laboratory experiments are conducted on a physical system in which an oscillatory, along-shore, free stream flow of a homogeneous fluid occurs in the vicinity of a long coastline with vertical slope; the model sea-floor is horizontal. Particular attention is given to the resulting rectified (mean) current which is along the coastline with the shore on the right, facing downstream. In the lateral far field region defined by (1), where y is the offshore coordinate and H is the depth of the fluid, the motion field is approximately independent of the lateral distance from the coast. The vertical structure of the cross-stream motion in this region consists of Ekman layers near the sea-floor and interior adjustment flows, both periodic in time. In the near field, defined by (1), the motion is strongly dependent on the cross-stream coordinate as well as time, and rectified currents are observed. The mechanism responsible for the rectification is a complex nonlinear coupling between laterally directed adjustment flows driven by the transport in the bottom Ekman layers, and the free stream motion field. The rectified current is found to be substantially wider than the Stewartson layer thickness but much narrower than the Rossby deformation radius. The characteristic width, δ_y, of the rectified current is shown to scale as , where Ro is the Rossby number Ro_t is the temporal Rossby number and E is the Ekman number. Experiments are presented which support this scaling.     

Microearthquake seismicity and fault-plane solutions in the southern Aegean and its geodynanic implications

Seismicity ( Ml <3.5) in the southern Aegean, located using data collected during seven weeks of recording by a temporary network of seismological stations, largely follows the Hellenic arc; the Sea of Crete is nearly aseismic, and only little activity is located south of the Hellenic trench, within the African plate. Focal mechanisms exhibit reverse faulting in the external part of the arc and normal faulting inside it. This normal faulting indicates N-S extension in the northern Aegean, the Gulf of Corinth, the Cyclades and Dodecanese Islands, but NW-SE extension in southern Peloponnese and western Crete and E-W extension in eastern Crete. This non-uniform strain pattern suggests that the Aegean region not only extends in a N-S sense, with the Hellenic arc moving south-westward relative to the Eurasian plate, but also by E-W extension of its southern margin, so that there is a net divergence of material.     

Job-Rich but Housing-Poor: The Dilemma of a Western Amenity Town*

Sedona, Arizona, an amenity town that trades on intangible quality-of-life attributes like spectacular scenery, the arts, and its nonmetropolitan location, has a conflict between low-wage employment catering to its tourist sector and expensive housing for its affluent residents. Many of those who work in Sedona do not live in the community. This study, based on a survey of 286 employees, shows that workers who live in Sedona do not have incomes that are significantly higher than commuters from the outside, but they live in housing that is almost twice as expensive. Employees who live in Sedona pay dearly for housing in order to be near jobs, natural beauty, and the cultural ambience of an amenity town. Commuters, on the other hand, incur high travel costs but enjoy cheaper housing and the lifestyle of small towns and rural areas. The emergence of amenity environments and long-distance commuting in Sedona is symbolic of the increased differentiation of nonmetropolitan landscapes.