Retardation of dissolved radiocarbon through a carbonated matrix     

Jean-Marie Garnier 《Geochimica et cosmochimica acta》1985,49(3):683-693

Spiked solutions (¹⁴C and ³H) were passed through two columns, one filled with silica and one with a mixture of silica and carbonate sand. Significant delay of ¹⁴C vs. ³H appeared in the second material and leads to a reduction of the relative flow rate which reaches 40%. Three types of effects causing modifications of the ¹⁴C transfer are analysed: (i) flow rate, (ii) sediment aging (iii) solution chemical composition and load. The reside with respect to water is governed by a linear process (assuming a constant number of reacting sites on the matrix) and kinetic process (where mass transfer effects are significant). It is also shown that much less than one mono-molecular layer of solid carbonate is involved and a distribution coefficient was estimated for these dynamic runs. Under field conditions, the interaction between ¹⁴C species (in the mobile and in the stationary phases) make ages obtained by ¹⁴C overestimated.  相似文献   

Efficiency test of earthquake prediction around Thessaloniki from electrotelluric precursors     

K. Meyer  P. Varotsos  K. Alexopoulos  K. Nomicos 《Tectonophysics》1985,120(1-2)

Since the completion of the network in January 1983, the electric field of the earth has been continuously monitored at four sites near Thessaloniki, the capital of northern Greece. From the present study and from previous investigations by similar measurements in Greece, it is evident that transient changes of the electrotelluric field occur prior to earthquakes. The analysis of these electric forerunners leads in many cases to a successful prediction of the epicentral area, the magnitude and the time of the impending event. Predictions prior to regional earthquakes are issued and documented with telegrams.From November 1983 until the end of May 1984 twelve earthquakes (M_L > 3.5) occurred in the vicinity of Thessaloniki. Ten of these were predicted and warnings given by telegram, whereas two smaller seismic events were missed. Two additional predictions were unsuccessful. Independent of their magnitudes, predicted events took place within a time window of 6 hrs to 6 days after the observations of the electrotelluric anomalies. The accuracy of the predicted epicenters in eight cases is better than 100 km, which corresponds roughly to the mean distance between the electric stations. Magnitude estimates deviate by less than 0.5 magnitude units from the seismically observed ones.Considering the two largest earthquakes, it is shown that the probability of making each of these predictions by chance is of the order of 10⁻².  相似文献   

Deglaciation and postglacial timberline in the San Juan Mountains,Colorado     

P.E. Carrara  W.N. Mode  Meyer Rubin  S.W. Robinson 《Quaternary Research》1984,21(1):42-55

Lake Emma, which no longer exists because of a mining accident, was a tarn in a south-facing cirque near the headwaters of the Animas River in the San Juan Mountains of southwestern Colorado. During the Pinedale glaciation, this area was covered by a large transection glacier centered over the Lake Emma region. Three radiocarbon dates on basal organic sediment from Lake Emma indicate that by ca. 15,000 yr B.P. this glacier, one of the largest in the southern Rocky Mountains, no longer existed. Twenty-two radiocarbon dates on Picea and Abies krummholz fragments in the Lake Emma deposits indicate that from ca. 9600 to 7800 yr B.P., from 6700 to 5600 yr B.P., and at 3100 yr B.P. the krummholz limit was at least 70 m higher than present. These data, in conjunction with Picea:Pinus pollen ratios from both the Lake Emma site and the Hurricane Basin site of J. T. Andrews, P. E. Carrara, F. B. King, and R. Struckenrath (1975, Quaternary Research 5, 173–197) suggest than from ca. 9600 to 3000 yr B.P. timberline in the San Juan Mountains was higher than present. Cooling apparently began ca. 3000 yr B.P. as indicated by decreases in both the percentage of Picea pollen and Picea:Pinus pollen ratios at the Hurricane Basin site (Andrews et al., 1975). Cooling is also suggested by the lack of Picea or Abies fragments younger than 3000 yr B.P. at either the Lake Emma or the Hurricane Basin site.  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   

Spectra of the earthquake sequence February-March, 1981, in south-central Sweden     

Ota Kulhnek  Torild Van Eck  Norris John  Klaus Meyer  Rutger Wahlstrm 《Tectonophysics》1983,93(3-4)

On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofM_L = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ M_L ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·10²⁰ resp. 4·10¹⁸dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.  相似文献   

GPS network monitors the Western Alps' deformation over a five-year period: 1993–1998     

C. Vigny  J. Chéry  T. Duquesnoy  F. Jouanne  J. Ammann  M. Anzidei  J.-P. Avouac  F. Barlier  R. Bayer  P. Briole  E. Calais  F. Cotton  F. Duquenne  K. L. Feigl  G. Ferhat  M. Flouzat  J.-F. Gamond  A. Geiger  A. Harmel  M. Kasser  M. Laplanche  M. Le Pape  J. Martinod  G. Ménard  B. Meyer  J.-C. Ruegg  J.-M. Scheubel  O. Scotti  G. Vidal 《Journal of Geodesy》2002,76(2):63-76

  The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at each site. GPS data processing has been done by three independent teams using different software. The different solutions have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and 2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation. Received: 27 November 2000 / Accepted: 17 September 2001  相似文献   

Climate change in Yellowstone National Park: Is the drought-related risk of wildfires increasing?     

Robert C. Balling Jr.  Grant A. Meyer  Stephen G. Wells 《Climatic change》1992,22(1):35-45

The increased frequency of wildfires in the United States has become a common prediction associated with the build-up of greenhouse gases. In this investigation, variations in annual wildfire data in Yellowstone National Park are compared to variations in historical climate conditions for the area. Univariate and multivariate analytical techniques reveal that (a) summer temperatures in the Park are increasing, (b) January-June precipitation levels are decreasing, and (c) variations in burn area within the Park are significantly related to the observed variations in climate. Outputs from four different general circulation model simulations for 2 × CO₂ are included in the analyses; model predictions for increasing aridity in the Yellowstone Park area are generally in agreement with observed trends in the historical climate records.  相似文献   

Glass crust on intratelluric phenocrysts in volcanic ash as a measure of eruptive violence     

J. D. Meyer 《Bulletin of Volcanology》1971,35(2):358-368

A comparison of each of the volumes of nine deposits of airborne volcanic ash from the Coatepeque Volcano in El Salvador, Central America to the amount of glass crust adhering to intratelluric phenocrysts shows an inverse relationship. As violence, volume, and eruptive abrasion increase, glass crusts decrease. The eruptive violence of a prehistoric eruption and the original volume of ash can thus be calculated from glass-to-crystal ratios observed in erosional remnants.  相似文献   

Luna 20: mineralogy and petrology of fragments less than 125 μm size     

Henry O.A. Meyer 《Geochimica et cosmochimica acta》1973,37(4):943-952

Two milligrams of less than 125 μm size particles from the Luna 20 soil sample (22001,17) have been examined. The results of the mineral identification and analysis verify earlier assumptions that the nature of the lunar highlands is predominantly anorthositic in composition. The presence of highly magnesian clinopyroxene, orthopyroxene and olivine suggests crystallization of Highland rocks in an ultrabasic environment. No fragments were observed that could be unequivocally assigned to mare basalt types.  相似文献   

Energy flow and elemental concentrations in the Steina River ecosystem (Black Forest, Germany)     

Giulio P. Genoni  Elisabeth I. Meyer  Andrea Ulrich 《Aquatic Sciences - Research Across Boundaries》2003,65(2):143-157

Considering food web energetics and elemental cycling together allows the testing of hypotheses about the coevolution of biological systems and their physical environment. We investigated the energy flow and the distribution of 25 elements in the Steina River.¶We constructed an annual energy flow network and estimated the emergy ("embodied energy" that includes all the energy involved in a process) contributions of resources sustaining the system. Furthermore, we measured the concentration of various macronutrients, essential elements, and heavy metals in the physical environment and trophic compartments. Finally, we examined the hypothesis of a positive relationship between the "rarity" of an element and its tendency to bioaccumulate. To do so, we used transformity, the relative energy input required to sustain a compartment's net production or the concentration differential of an element between the living community and the physical environment.¶The resulting energy flow network is one of the most complete available for streams. In the Steina, over 99% of the energy input is transported through the system without being processed. Dissolved inorganic matter and sunlight are the largest inputs, but uptake efficiency is much higher for dissolved and particulate organic matter. Transformities of trophic compartments and elements span 6 to 7 orders of magnitude.¶The tendency to bioaccumulate was as predicted for most elements, with macronutrients showing no accumulation and heavy elements accumulating in high-transformity compartments. However, Na and K were found at highest concentrations in consumers, and Pb, Ga, and Cd in algae. Improved estimates may become possible as more knowledge is available on ecosystem flows. We suggest further ways of testing hypotheses about strategies of element processing.  相似文献