Radar observations of prevailing winds and waves in the Southern Hemisphere mesosphere and lower thermosphere     

A. Phillips  R. A. Vincent 《Pure and Applied Geophysics》1989,130(2-3):303-318

HF radar stations (utilizing the spaced-antenna partial-reflection technique) located at Adelaide (35°S, 138°E) and Mawson Station (67°S, 63°E) have observed horizontal mesospheric winds continuously since mid-1984. Observations in the period 1984–87 are compared with the Northern Hemisphere [latitude conjugate] stations of Kyoto (35°N, 136°E) and Poker Flat (65°N, 147°W), and with satellite-derived circulation models. Particular reference is made to the equinoctial changeovers in zonal flow and to the temporal and altitude variations in the planetary wave activity at Mawson and Adelaide.  相似文献   

March 1986 eruptive episodes at Piton de la Fournaise volcano (Reunion Island)     

H. Delorme  P. Bachlery  P.A. Blum  J.L. Chemine  J.F. Delarue  J.C. Delmond  A. Hirn  J.C. Lepine  P.M. Vincent  J. Zlotnicki 《Journal of Volcanology and Geothermal Research》1989,36(1-3)

From May 1985 to April 1986 five discrete eruptions have occurred at Piton de la Fournaise volcano. On March the 17th, a sixth episode began with four distinct stages. They took place along the southeast rift zone of the volcano, from the summit to the sea coast. It was the first rift zone eruption in the south since 1800 A.D. and the first ever monitored at Piton de la Fournaise volcano.Three fissural vents opened at decreasing altitude emitting about 12 to 15 × 10⁶ m³ of olivine basalts between 19th March and 1st April. Strong seismic activity was accompanied by deformation of the summit area, and large-scale variations of the magnetic field. A summital event characterized the end of the flank activity with collapse of a new pit-crater and outflow of small amounts of degassed aphyric basalt.  相似文献   

Application of the weighted residual method to diffraction by 2-D canyons of arbitrary shape: I. Incident SH waves   总被引：1，自引：0，他引：1  

Vincent W. Lee  Xiaoyun Wu 《Soil Dynamics and Earthquake Engineering》1994,13(5)

A solution for the two-dimensional scattering and diffraction of plane SH waves by canyons of arbitrary shape in an elastic half space is presented. The wave field for arbitrary geometry in this paper is computed numerically by the method of weighted residues (moment method). The wave displacement field computed by the present residual method for the case of a semi-circular canyon was shown to agree analytically and numerically with that computed by the exact closed form series solution. The same observations about ground amplifications, their dependence on frequencies and orientations of the incident waves, can be stated here for canyons of arbitrary shape as previously made for circular canyons.  相似文献   

Book reviews     

Yukio Fujinawa  A. V. Koloskov  Gerardo G. Tango  Lech Stefaníak  Douglas R. Schmitt  Kei Katsumata  Vernon F. Cormier  Wladislaw Lyatsky  Krzysztof Haman  P. Vincent  Konrad Bajer  Henryk Piwkowski 《Pure and Applied Geophysics》1991,136(2-3):343-367

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Instantaneous velocity of mid-ocean ridges     

Vincent S. Cronin 《Tectonophysics》1994,230(3-4):151-159

Intuition suggests that all points on the same mid-ocean ridge should rotate around the relative pole of the two-plate system at the same instantaneous angular velocity. Contrary to intuition, the instantaneous angular velocity of a ridge varies from one point to another along the ridge, given the general case in which two plates move around different plate-specific poles of rotation. The variation in the instantaneous angular velocity of a ridge is a function of the motion characteristics of the plates and the position of the ridge relative to the poles of plate motion. The length or orientation of individual ridge segments is predicted to vary over time, leading to local changes in the shape of the ridge. The gradient in instantaneous angular velocity for the fast-spreading East Pacific Ridge, between the Cocos and Pacific plates, is an order of magnitude greater than the gradient along the Mid-Atlantic Ridge, between the North American and African plates. This great contrast in ridge instantaneous velocity gradients may be reflected in the contrasting ridge geometries of the East Pacific and Mid-Atlantic Ridges.  相似文献   

Two-step deglaciation: 14C-Dated high-resolution δ18O records from the tropical Atlantic Ocean     

W.H. Berger  J.S. Killingley  C.V. Metzler  E. Vincent 《Quaternary Research》1985,23(2):258-271

Eight box cores from the tropical Atlantic were studied in detail with regard to foraminiferal oxygen isotopes, radiocarbon, and Globorotalia menardii abundance. A standard Atlantic oxygen-isotope signal was reconstructed for the last 20,000 yr. It is quite similar to the west-equatorial Pacific signal published previously. Deglaciation is seen to occur in two steps which are separated by a pause. Onset of deglaciation is after 15,000 yr B.P. The pause is centered between 11,000 and 12,000 yr B.P., but may be correlative with the Younger Dryas (10,500 yr B.P.) if allowance is made for a scale shift due to mixing processes on the sea floor. Step 2 is centered near 10,000 yr B.P. and is followed by a brief excursion toward light oxygen values. This excursion (the M event) may correlate with the Gulf of Mexico meltwater spike.  相似文献   

Equilibrium state of diopside-bearing harzburgites from ophiolites: Geobarometric and geodynamic implications   总被引：5，自引：0，他引：5  

Jean -Claude C. Mercier  Vincent Benoit  Jacques Girardeau 《Contributions to Mineralogy and Petrology》1984,85(4):391-403

The bulk compositions of coexisting enstatite and diopside in basal lherzolites and clinopyroxene-bearing harzburgites from ophiolitic complexes are typical of solidus/subsolidus equilibria, but for a few texturally distinct magmatic diopsides. They would presumably reflect the state of equilibrium at the time they last coexisted with liquid as the rocks reentered subsolidus conditions. The total lack of correlation between Al and Ca concentrations shows that the compositional scatter observed for any given massif, results from analytical errors related to extensive exsolution and serpentinization, rather than from differences in equilibrium conditions. However, significant differences are found between the residual ophiolitic lherzolites from Hare Bay, Newfoundland, and from Xigaze, Tibet, two massifs selected for their distinct structural and textural features. As for thermobarometry techniques relevant to these rocks, the best barometer found is an empirical relation for the expression of pressure as a virtually temperature-independent function of the ratioK _f=(X _Di ^opx )/(1 –X _Di ^cpx ), in agreement with semi-quantitative models based on natural solid solutions. Temperatures are then simply derived from a surface-fitting expression relating pressure, temperature and diopside-solvus compositions, according to a regularX _En ^cpx solution model (CMS) corrected for the effect of Al in the spinel facies. Application of these techniques yield pressures of 0.4 and 1.4 GPa, i.e. depths from sea-bottom of about 13 and 43 km, for temperatures of 1,170 and 1,300° C for the ophiolitic lherzolites of Tibet and New-foundland, respectively, in good agreement with dry-solidus data by radioactive tracing and with geothermal-model estimates for ridges.  相似文献   

Rocking strong earthquake accelerations     

Vincent W. Lee  Mihailo D. Trifunac 《Soil Dynamics and Earthquake Engineering》1987,6(2)

In this paper, the method presented by Lee and Trifunac (1985) for generating synthetic torsional accelerograms has been extended to the estimation of synthetic rocking accelerograms and of their response spectra. Results from our previous regression analyses for the characterization of strong shaking in terms of (1) earthquake magnitude and epicentral distance, or (2) Modified Mercalli Intensity at the site are utilized here again. The effects of geologic environment, in terms of site parameters or the representative depth of sediments, which influence amplification, and the dispersive properties of ground motion are also included. The synthetic rocking accelerogram is then constructed from the horizontal and vertical acceleration components.  相似文献   

Petrologic evolution of Krakatau (Indonesia): Implications for a future activity     

G. Camus  A. Gourgaud  P.M. Vincent 《Journal of Volcanology and Geothermal Research》1987,33(4)

Krakatau Volcano is located along a N35E volcanic lineament running through the Sunda straits (Indonesia). Its last activity has been characterized by successive phases, each beginning with the construction of a cone, and ending with its destruction and the formation of a caldera. The two last (pre- and post-1883) cycles are well known, but the more ancient ones are not so clearly defined.Lavas of Krakatau belong to an andesitic series, in which fractional crystallization plays the most important role. The petrologic evolution is characterized by a cyclicity in good agreement with the structural evolution: the succession is regular: basalts, basic andesites, acid andesites, dacites. A gap between acid and basic andesites occurs in each cycle. The destructive stages correspond to the occurrence of dacitic terms.The Anak cycle was characterized from 1927 to 1979 by basalts and basic andesites; the 1981 eruption involved a more differentiated magma (close to dacitic). Detailed study of the petrologic evolution since 1883 emphasizes the predominant role of fractional crystallization. This process occurred during a very short period, between 1979 and 1981. Separation of labradorite, augite, olivine and magnetite from parental basic andesite may generate the dacitic descendant, in a shallow reservoir (P_H2O estimated about 0.5 kbar). Implications for a future activity are considered.  相似文献   

Eruptive history of the Colima volcanic complex (Mexico)     

Claude Robin  Philippe Mossand  Guy Camus  Jean-Marie Cantagrel  Alain Gourgaud  Pierre M. Vincent 《Journal of Volcanology and Geothermal Research》1987,31(1-2)

The evolution of the Colima volcanic complex can be divided into successive periods characterized by different dynamic and magmatic processes: emission of andesitic to dacitic lava flows, acid-ash and pumice-flow deposits, fallback nuées ardentes leading to pyroclastic flows with heterogeneous magma, plinian air-fall deposits, scoriae cones of alkaline and calc-alkaline nature. Four caldera-forming events, resulting either from major ignimbrite outbursts or Mount St. Helens-type eruptions, separate the main stages of development of the complex from the building of an ancient shield volcano (25 × 30 km wide) up to two summit cones, Nevado and Fuego.The oldest caldera, C1 (7–8 km wide), related to the pouring out of dacitic ash flows, marks the transition between two periods of activity in the primitive edifice called Nevado I: the first one, which is at least 0.6 m.y. old, was mainly andesitic and effusive, whereas the second one was characterized by extrusion of domes and related pyroclastic products. A small summit caldera, C2 (3–3.5 km wide), ended the evolution of Nevado I.Two modern volcanoes then began to grow. The building of the Nevado II started about 200,000 y. ago. It settled into the C2 caldera and partially overflowed it. The other volcano, here called Paleofuego, was progressively built on the southern side of the former Nevado I. Some of its flows are 50,000 y. old, but the age of its first outbursts is not known. However, it is younger than Nevado II. These two modern volcanoes had similar evolutions. Each of them was affected by a huge Mount St. Helens-type (or Bezymianny-type) event, 10,000 y. ago for the Paleofuego, and hardly older for the Nevado II. The landslides were responsible for two horseshoe-shaped avalanche calderas, C3 (Nevado) and C4 (Paleofuego), each 4–5 km wide, opening towards the east and the south. In both cases, the activity following these events was highly explosive and produced thick air-fall deposits around the summit craters.The Nevado III, formed by thick andesitic flows, is located close to the southwestern rim of the C3 caldera. It was a small and short-lived cone. Volcan de Fuego, located at the center of the C4 caldera, is nearly 1500 m high. Its activity is characterized by an alternation of long stages of growth by flows and short destructive episodes related to violent outbursts producing pyroclastic flows with heterogeneous magma and plinian air falls.The evolution of the primitive volcano followed a similar pattern leading to formation of C1 and then C2. The analogy between the evolutions of the two modern volcanoes (Nevado II–III; Paleofuego-Fuego) is described. Their vicinity and their contemporaneous growth pose the problem of the existence of a single reservoir, or two independent magmatic chambers, after the evolution of a common structure represented by the primitive volcano.  相似文献