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Fault lengths, distributions and orientations were determined at six post-Jurassic horizons in the Porcupine Basin, offshore Ireland. Three rifting periods occurred in the Porcupine Basin with fault orientations and lengths measured for the second and third of these. Dominant fault directions changed through time, while remaining broadly parallel to the basin margins, particularly in the southern part of the basin and especially for the larger faults. Observed changes in activity suggest that strain was evenly distributed throughout the basin during the periods of extension. Length population curves for the faults throughout the basin show an approximate straight line log-log relationship between cumulative number and fault length, indicating that the fracture length populations are self-similar over a range of scales. The fault patterns reflect the response to the transition from a syn-rift dominant phase of basin evolution to one where the development was primarily influenced by thermal subsidence with subsidiary rifting.

About 6,000 specific-gravity (SG) measurements of samples collected from nearly 200 granitic plutons comprising the central Sierra Nevada batholith yield a SG contour map across the batholith from 36.25° to 38° north latitude. With notable exceptions, SG decreases from values generally greater than 2.7 in the west to less than 2.6 over a few small areas of high-silica, high-potassium granites near the east edge. A good correlation between measured SG and analyzed weight percent SiO2 enables estimation of average silica variations across the batholith. The average SG is 2.69 corresponding to an average of 68 wt. % SiO2 for the 18,000 km² central part of the batholith. A 1-km gridded version of the SG measurements has been used to generate a series of synthetic gravity maps, assuming that the SG of rocks at the surface extends unchanged to various depths. The synthetic map computed for a depth of 10 km shows the best correspondence with the isostatic residual gravity map indicating that variations in the observed gravity residuals are largely caused by SG variations of the plutonic rocks exposed at the surface that apparently extend downward to an average depth of about 10 km. Although the 10-km synthetic gravity map gives the best overall fit to the observed gravity data, comparison of individual anomalies indicates that the bottoms of the plutons as defined by SG variations at the surface are generally shallower along the west edge of the Sierra Nevada (7±2 km) and deeper in the younger and more felsic eastern part (12±3 km). These depths do not necessarily represent a distinct base of the Sierra Nevada batholith. They may indicate the depth below which density homogenization occurs, either by igneous, or possibly, structural processes.

The Porcupine, Rockall and Hatton–Rockall basins lie on the continental seaboard west of Ireland. Up to 9 km of Cretaceous and Tertiary strata are preserved in the Porcupine Basin, in contrast to 2–3 km in the Rockall and Hatton–Rockall basins. Differences in seismic stratigraphic sequences through the region are attributed to an interplay between the developing North Atlantic Ocean, post-rift thermal subsidence and sea-level changes. Localized Ryazanian fault-controlled alluvial fan clastic rocks in the Porcupine Basin are succeeded by Valanginian to Barremian marine deposits. Sea-level lowstands in Albian and Paleocene–Eocene times, interpreted as rift and ridge-push effects respectively, resulted in delta and submarine fan progradation. Rapid thermal subsidence in Early Oligocene times led to marine deposits and to the onset of geostrophic currents. Miocene slumping triggered shale-dominant turbidite development, followed by tranquil deep marine sediments as subsidence outstripped sedimentation. The Cretaceous sequence in the Rockall Trough is thought to contain extensive igneous bodies overlain by an Upper Cretaceous muddy chalk sequence which is cut by abundant Tertiary sills and dykes. A number of shale-prone Upper Tertiary sequences occur. The Upper Cretaceous to Lower Tertiary succession is thin and frequently absent in the Hatton–Rockall Basin.

Extensional tectonism is clearly a major factor in the formation of sedimentary basins. Tectonism influences many of the factors which control sediment deposition and preservation including: rates and styles of basin subsidence, accommodation space, drainage area size and topography, and rates of sediment input. These tectonically-influenced factors are interrelated and their local interplay determines, to a great extent, the formation, composition and structural style of sedimentary sequences.

First results are reported of a comprehensive campaign to measure ionospheric structure and dynamics of nighttime polar cap F‐layer or F‐region arcs. Airborne optical and digital ionosonde data were collected simultaneously with ground based incoherent scatter radar data, continuously over many hours in time and 500 to 1000 km in space. Polar cap F‐region sub‐visual auroral arcs, which are commonly observed during quiet magnetic conditions, are found to represent boundaries (or shears) in the polar cap plasma circulation pattern. F‐region electron concentration enhancements are found in these features and can be of significance to polar thermospheric circulation, composition, and thermal structure. The quiet polar ionosphere is so structured that high time resolution intensified optical images of thermospheric emmissions can make a major contribution to interpretation of incoherent scatter radar data.

All-sky imaging photometer measurements and ionospheric soundings taken at Thule, Greenland (86° corrected geomagnetic latitude), in December 1979 and January 1982 reveal the large-scale organization of the winter polar cap ionosphere. Three groups of forms have been identified: (1) The most predominant features are sun-aligned, generally unstructured, subvisual, F region arcs, extending for more than 1000 km (limit of all-sky field of view) across the polar cap. In general, these arcs drift from dawn to dusk at speeds between 100 and 250 m s−1; however, stagnation of arc drift and drift reversals have been observed. The arcs are produced by soft particle precipitation. (2) During a magnetically disturbed period the arcs disappeared, and large patches of enhanced F region ionization drifted at speeds of 250 to 700 m s−1 across the field of view in the antisunward direction. Although arcs are produced by soft particle precipitation, preliminary results from the Dynamics Explorer satellite do not indicate any localized soft electron precipitation into the patches. (3) On a few occasions both forms were observed simultaneously. Between F region sun-aligned arcs, which were drifting from dawn to dusk, small patches of ionization were observed moving at much higher speed in the antisunward direction. Both the arcs and the patches appear as strong localized irregularities in the ionospheric soundings. The Doppler information provided by the aircraft's Digisonde 128PS was used to relate backscatter traces to individual arcs or patches and to track individual features over more than 1500 km. For a large number of observations the time variation of measured Doppler velocities suggests specular reflection from electron density enhancements associated with the optical forms, rather than scatter from field-aligned irregularities imbedded in the arcs or patches. A simple velocity filter applied to the ionogram data permitted the generation of range-time characteristics for selected ionization drift velocities. A tendency for high velocities to occur during magnetically active periods was found. The ionospheric soundings showed that the F region arcs are bands of enhanced ionization, imbedded in a background ionosphere with a base height (h′F) of approximately 250 km and a critical frequency of approximately 4 MHz (∼2 × 105 el cm−3). The virtual heights in the ionograms did not change during transit of the arcs through the zenith. During the active periods, when the antisunward moving patches were observed, the background ionization dropped to less than 3 MHz (105 el cm−3) while the base height (h′F) moved up to heights above 400 km. The strongly ionized patches (f0 F2 > 8 MHz), however, were observed to reach a minimum virtual range of ∼250 km during the zenith transit, leading during their passage through the zenith to rapid h′F fluctuations of the order of 200 km within minutes.

This investigation deals with the effects of leaching of the organic and inorganic constituents on the shear strength and compressibility of a near-surface marine sediment. The method of investigation consisted of determining the shear strength, stress–strain and consolidation characteristics of both the untreated and treated sediment. Types of treatment performed were: leaching with acetic acid to remove the inorganic cations; leaching with sodium hydroxide to remove the organic matter; permeating with artificial sea water to observe the hydraulic effects of the leaching process. The untreated sediment exhibited behaviour, during both shear and consolidation, which was characteristic of an overconsolidated sediment. Consideration of the possible sources of this behaviour led to the assumption that it was due to physico-chemical effects, particularly cementation or bonding. The acetic acid-leached and sea water-permeated samples exhibited behaviour very similar to that of the untreated sediment. The sodium hydroxide-leached samples, however, showed no over consolidation characteristics, either in shear or consolidation, thus confirming the assumption that cementation or bonding was the cause of the overconsolidation behaviour observed in the other tests. Chemical analyses of the leachate and sediment were performed with the view of correlating the observed changes in geotechnical properties with the chemical changes produced by leaching. From the observed differences in geotechnical behaviour before and after leaching, a structural bonding hypothesis is developed to explain the overconsolidated characteristics of the sediment. Cette recherche concerne les effets des constituants organiques et inorganiques lessivés, sur la résistance à la rupture au cisaillement et la compressibilité d'un sédiment marin proche de la surface. La méthode de recherche se compose de la détermination de la résistance à la rupture au cisaillement, de la contrainte-déformation et des caractéristiques de consolidation des sédiments aussi bien non traités que traités. Les types de traitement exécutés furent: lessiver avec de l'acide acétique pour enlever les cations inorganiques, lessiver avec de l'hydroxyde de sodium pour enlever la matière organique et imbiber d'eau de mer artificielle afin d'observer les effets hydrauliques du procédé de lessivage. Le sédiment non traité montra un comportement, pendant le cisaillement aussi bien que la consolidation, qui fut caractéristique d'un sédiment surconsolidé. L'examen des causes possibles de ce comportement conduisit à supposer qu'il résultait des effets physico-chimiques, particulièrement de cémentation ou de liaison. Des échantillons imprégnés d'acide acétique et d'eau de mer montrèrent un comportement très sémblable au sédiment non traité. Cependant, les échantillons lessivés avec de l'hydroxyde de sodium ne montrèrent aucune caractéristique de surconsolidation, confirmant ainsi la supposition que la cémentation ou la liaison soit la cause du comportement de surconsolidation observé dans les autres expériences. Des analyses chimiques du lessivage et du sédiment furent exécutées dans le but de mettre en corrélation les changements observés dans les propriétés géotechniques avec les changements chimiques produits par le lessivage. A partir des différences observées dans le comportement géotechnique avant et après le lessivage, une hypothèse de liaison structural est proposée afin d'expliquer les caractéristiques de surconsolidation du sédiment.

The height of maximum luminosity of an auroral arc is estimated from simultaneous observations at three stations in western United States during a night of general auroral activity (November 27–28, 1959). Photometrically this arc is characterized by a selective enhancement of the [O I] 6300 A line. From twenty-four individual measurements the height is found to be 412 km with a standard deviation of ±23 km for one observation and ±5 km for the mean. The geographical position of the arc, its orientation, and its movement during the night are discussed.

Solid-electrolyte sensors were used to measure the oxygen and sulphur fugacities of magmatic gases in vents located at an elevation of about 3170 m on the northeast flank of the NE crater of Mt Etna in July 1970. The temperature of the gas ranged from 773 to 1057 °C. The least-squares fit of 13 measured lgfo2 values yielded the relation: lg/o2 (atm) = 2.175- 15110/T (K), which gives values of 0.9 to 2.2 lgfo2 units higher than those obtained in the Makaopuhi lava lake, Hawaii, within the temperature range measured, the difference increasing with decreasing temperature. Laboratory study of a water-quenched sample of the Etna lava and calculations of gas equilibria indicate that the difference is due partly to the intrinsically higher f 02 of the Etna magma and partly to the mixing of air with the Etna gases. The measured j^2 value was 10-2 4 atm at 860 °C.