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1.
In this paper we try to explain the empirical Na---K---Ca geothermometer introduced by Fournier and Truesdell (1973).At high temperatures (100°C < t < 370°C), the geothermometer can be related to an equilibrium between plagioclase, K-feldspar and water. If this is true, plagioclase must have a nearly constant composition, rich in albite. At low temperatures, the relation between temperature and the Fournier and Truesdell formula can be explained by an increase of the total concentration of dissolved salts with temperature. This increase and the increase of temperature calculated by the Fournier and Truesdell relation can be related to other effects, among which one of the most important is that we deal with a quasi-closed system.
Résumé
Dans cet article on essaye d'expliquer le géothermométre empirique de Fournier et Truesdell (1973) utilisant les concentrations en sodium, potassium et calcium dissous dans les eaux.A haute température (100°C < t < 370°C), le thermométre peut être expliqué par un équilibre entre plagioclase, feldspath potassique et eau, á condition que le plagioclase ait une composition á peu prés constante et trés proche du pôle albite. A basse température, la liaison entre la température et la formule de Fournier et Truesdell peut s'expliquer par une augmentation de la concentration globale en sels dissous, á composition relative constante, avec la température. Mais l'augmentation de la concentration globale et par suite l'augmentation de la température calculée peut être également due á d'autres facteurs dont le principal est le confinement de la solution. 相似文献2.
In the upper catchment of the River Loire, France, the construction of five reservoir dams has been planned to sustain the low flows in the Loire valley. The management of these reservoirs, to be built successively, must be approached from partial or complete points of view in order to establish the daily draft decisions at every stage of the project.A hydrological criteria concerning the low flows at a station in the valley (namely the “objective point”) is used to judge the results. It is possible to determine the optimal carry-over storage for this criterion with the use of a long series of simulated inflows to reservoirs and annual deficits, when the future conditions are presumed to be known. The statistical analysis of the results helps in the formulation of the objectives for long-term Q1 assuring the carry-over storage for a predetermined risk of failure.This objective for long-term Q1 will not hold good if the low flow is severe. Thus some deterministic and statistical hypotheses have been used to formulate an objective for the mean term of flow Q2 (tj) which is calculated each day tj and adjusted to the hydrological conditions of the year. The target draft Cb at the objective point is the minimum of the pair [(Q1, Q2 (tj)].Water is discharged each day to meet this target flow, while maintaining all the constraints of the flows downstream to the reservoirs. It takes into account the time needed for transfer of water and permits a good prediction of either the flow propagation in the upper watershed or the evolution of the inflows from downstream catchments.A modular model is used to calculate the daily flow. The results obtained from simulation were satisfactory.
Résumé
La construction de cinq barrages réservoirs est envisagée sur le haut-bassin de la Loire, en vue de soutenir les débits d'étiage dans la basse vallée. Une gestion en temps réel s'exprime par une formulation journalière des débits à lacher aux ouvrages de retenue. Cette formulation résulte d'une optimisation de la gestion des volumes d'apports, compte tenu d'une contrainte de défaillance liée à un état vide des réserves en cours d'étiage.La recherche de la gestion optimale des reports interannuels est faite au moyen d'un critère purement hydrologique: la distribution de probabilité des débits d'étiage en une station de la vallée, appelée point objectif. Une longue série simulée d'apports annuels aux réservoirs et de déficits au point objectif permet de déterminer les reports interannuels optimaux vis-à-vis de ce critère dans le cas d'un avenir certain. L'analyse statistique des reports effectués dans ces conditions permet de dégager la formulation d'un objectif à long terme assurant un report interannuel pour un risque déterminé de défaillance. Cet objectif défini en début de saison d'étiage et optimisant le report envisagé est appelé l'objectif à long terme Q1. En cas de réserves assez faibles en début de saison, et d'étiage plus sévère que prévu, le maintien “ne varietur” de cet objectif peut conduire à la vidange totale des réservoirs en cours d'étiage. Une contrainte journalière a été ajoutée pour limiter ce risque. La répartition de la totalité des réserves disponibles sur la période probable d'étiage restant à courir, définit un objectif à moyen terme Q2 (tj). Sa réactualisation chaque jour évite toute défaillance brusque de la gestion. Le débit que l'on cherche à maintenir au point objectif ou débit cible est défini chaque jour par le minimum du couple [Q1, Q2 (tj)].La réalisation pratique de ce débit cible à partir des délestages effectués aux différents barrages tient compte de la propagation des débits lachés et des prévisions d'apports des bassins intermédiaires. Un modèle modulaire de bassin a été conçu qui permet le calcul des lachures journalières réalisant un débit cible défini.La simulation de la méthode proposée sur les séries historiques disponibles fournit des résultats très satisfaisants. 相似文献3.
S. de la Cruz-Reyna M.A. Armienta V. Zamora F. Jurez 《Journal of Volcanology and Geothermal Research》1989,38(3-4)
Local seismic activity consisting of sharp earthquakes accompanied by thunderous noise was reported starting in late December 1985 around Tacaná volcano (15.13°N, 92.10°W). Portable seismic stations were established in the area by late January 1986 and sampling of the only known thermal spring on the volcano flanks started at the same time. A marked increase in SO42− concentration in the spring water preceded by two months the occurrence of a seismic swarm crisis and a small phreatic explosion. A model involving a crystalline basement fractured by tectonic stresses is proposed to explain the chemical and seismic anomalies, and the consequences on risk of volcanic activity are briefly discussed in terms of the observed behaviour. 相似文献
4.
Atmospheric gravity wave propagation direction observed by airglow imaging in the South American sector 总被引：1，自引：0，他引：1
A.F. Medeiros H. Takahashi R.A. Buriti K.M. Pinheiro D. Gobbi 《Journal of Atmospheric and Solar》2005,67(17-18):1767
Airglow all sky imaging observation has been carried out in three different locations in south America, at Cachoeira Paulista (22.7°S, 45.0°W) in 1999, São João do Cariri (7.5°S, 36.5°W) in 2001 and Boa Vista (2.8°N, 60.7°W) in 2002. Comparing the atmospheric gravity wave characteristics retrieved from the image data for the three different sites and including a previous work at Alcântara (2.3°S, 44.5°W) carried out by Taylor et al. [1997. Journal of Geophysical Research 102 (D22) 26,283–26,299], we found that there is a preferential propagation direction, from the Continent to the Atlantic Ocean. The observed wave propagation directions reveal that a major part of the waves have their direction from Continent toward Ocean. The possible source of the wave generation is discussed. 相似文献
5.
Seismicity, seismic input and site effects in the Sahel—Algiers region (North Algeria) 总被引：2，自引：0，他引：2
A. Harbi S. Maouche F. Vaccari A. Aoudia F. Oussadou G.F. Panza D. Benouar 《Soil Dynamics and Earthquake Engineering》2007,27(5):427-447
Algiers city is located in a seismogenic zone. To reduce the impact of seismic risk in this Capital city, a realistic modelling of the seismic ground motion (SGM) is conducted by using the hybrid method that combines the finite differences method and the modal summation. For this purpose, a complete database of geological, geophysical and earthquake data is constructed. A critical re-appraisal of the seismicity of the zone [2.25°E–3.50°E, 36.50°N–37.00°N] is performed and an earthquake list, for the period 1359–2002, is compiled. The analysis of existing and newly retrieved macroseismic information allowed the definition of earthquake parameters of macroseismic events for which a degree of reliability is assigned. Geological cross sections have been built up to model the SGM in the city, caused by the 1989 Mont-Chenoua and the 1924 Douéra earthquakes. Synthetic seismograms and response spectral ratio is produced for Algiers, and they show that the soft sediments in Algiers centre are responsible of the noticed amplification of the SGM. 相似文献
6.
D. D. Singh 《Journal of Geodynamics》2000,30(5):159
The centroid-moment tensor solutions of more than 300 earthquakes that occurred in the Himalayas and its vicinity regions during the period of 1977–1996 are examined. The resultant seismic moment tensor components of these earthquakes are estimated. The Burmese arc region shows prominent east–west compression and north–south extension with very little vertical extension. Northeast India and Pamir–Hindu Kush regions show prominent vertical extension and east–west compression. The Indian plate is subducting eastward beneath the northeast India and Burmese arc regions. The overriding Burmese arc has overthrust horizontally with the underthrusting Indian plate at a depth of 20–80 km and below 80 km depth, it has merged with the Indian plate making “Y” shape structure and as a result the aseismic zone has been formed in the region lying between 26°N–28°N and 91.5°E–94°E at a depth of 10–50 km. Similarly, the Indian plate is underthrusting in the western side beneath the Pamir–Hindu Kush region and the overriding Eurasian plate has overthrust it to form a “Y” shape structure at a depth of 10–40 km and below 60 km depth, it has merged with the Indian plate and both the plates are subducting below 60–260 km depth. Further south, the overriding Eurasian plate has come in contact with the Indian plate at a depth of 20–60 km beneath northwest India and Pakistan regions with left lateral strike slip motion. 相似文献
7.
Lack of water supply during periods of deficient flow affects the economic potentiality of the great river valleys which are the most developed areas in the country. Reservoir dams built in the upper stream catchments store excess flow and provide controlled release in the dry season. Capital costs of construction and the consequences of failures justify a thorough study of operating rules.The low flows and conditional variability of availability of water call for carry-over procedures (reservoir capacity is sometimes greater than the mean available water). It is not possible to predict future sequence of flows, thus the carry-over rule is a statistical decision-making tool. The flow data are only one of the very many possible sources of information. But the analysis of flow data provides us with statistical measures to generate long series of synthetic inflows associated with summer deficits.A simplification has been introduced by choosing only the values which are absolutely necessary for optimal management research: available water volumes and reserve volumes for a flow threshold.Yearly alternate periods of excess and deficiency of water are defined by the values above and below a threshold of flow discharge at a location gage named “objective point”, where the reservoir effects are to be estimated. Yearly periods are described by water volumes, either inflows into reservoirs, or deficits below various thresholds of summer flow discharges. Marginal and conditional probability distributions of these volumes and the physical laws which mark their bounds and relationships were estimated on the basis of 31 years of daily flow records.The synthetic simulated series for 1000 years was compared to records of historical levels (since 1863). Extreme events such as sequences of dry years, have return periods of comparable magnitude.This synthetic series has a similar statistical character of short historical series and makes the analysis of operating rules possible.
Résumé
Les moyennes et basses vallées des fleuves ont en général polarisé le développement industriel et agricole, créant ainsi des besoins en eau croissants. L'implantation de barrages-réservoirs dans les hauts bassins peut contribuer à atténuer les graves conséquences de pénuries. Ils emmagasinent l'eau en période d'abondance et la restituent en étiage. L'importance des investissements et les conséquences d'une défaillance justifient une analyse minutieuse des conditions de gestion de ces retenues.L'aménagement du bassin de la Loire (France) prévoit des réservoirs de capacités importantes vis-à-vis des apports annuels moyens. La variabilité liée des étiages et des apports aux réservoirs, conduit à envisager des reports interannuels. La valeur optimale du report a un caractère statistique, en raison de l'indépendance des caractères hydrologiques des années successives.Une simplification a été recherchée, ne comportant que les grandeurs strictement indispensables à la recherche de la gestion optimale: volumes d'apports et volumes de soutien à un seuil de débit. Les périodes d'apports et de déficits sont définies annuellement par le franchissement d'un seuil de débit à la section objectif du soutien. Les états alternés ainsi obtenus sont caractérisés: (1) pour la période d'apports: par les volumes apportés aux divers réservoirs; et (2) pour la période de déficit: par les volumes déficitaires sous différents seuils de débit au point objectif.Les 31 années d'observations de débits dans le bassin ont permis l'estimation des lois de distributions marginales et liées de ces variables, ainsi que des contraintes physiques qui les bornent. Cette analyse a permis l'élaboration d'un modèle de génération simultanée d'apports aux réservoirs et d'étiages dans la vallée. Une série longue de 1000 ans a ensuite été générée par une méthode de Monte-Carlo.Les résultats de la simulation ont été confrontés aux observations historiques de hauteurs d'eau (110 ans). Les événements exceptionnels ont des fréquences d'ordre de grandeur comparable.Cette série synthétique permet d'envisager une analyse de la gestion dégagée du caractère particulier lié à la brièveté de la série historique. 相似文献8.
Gail A. Mahood Alfred H. Truesdell Luis A. Templos M 《Journal of Volcanology and Geothermal Research》1983,16(3-4)
The Sierra La Primavera, a late Pleistocene rhyolitic caldera complex in Jalisco, México, contains fumaroles and large-discharge 65°C hot springs that are associated with faults related to caldera collapse and to later magma insurgence. The nearly-neutral, sodium bicarbonate, hot springs occur at low elevations at the margins of the complex, whereas the water-rich fumaroles are high and central.The Comisión Federal de Electricidad de México (CFE) has recently drilled two deep holes at the center of the Sierra (PR-1 and Pr-2) and one deep hole at the western margin. Temperatures as high as 285°C were encountered at 1160 m in PR-1, which produced fluids with 820 to 865 mg/kg chloride after flashing to one atmosphere. Nearby, PR-2 encountered temperatures to 307°C at 2000 m and yielded fluids with chloride contents fluctuating between 1100 and 1560 mg/kg after flashing. Neither of the high-temperature wells produced steam in commercial quantities. The well at the western margin of the Sierra produced fluids similar to those from the hot springs. The temperature reached a maximum of 100°C near the surface and decreased to 80°C at 2000 m.Various geothermometers (quartz conductive, Na/K, Na-K-Ca, δ18O(SO4-H2O) and D/H (steam-water) all yield temperatures of 170 ± 20°C when applied to the hot spring waters, suggesting that these spring waters flow from a large shallow reservoir at this temperature. Because the hot springs are much less saline than the fluids recovered in PR-1 and PR-2, the mixed fluid in the shallow reservoir can contain no more than 10–20% deep fluid. This requires that most of the heat is transferred by steam. There is probably a thin vapor-dominated zone in the central part of the Sierra, through which steam and gases are transferred to the overlying shallow reservoir. Fluids from this reservoir cool from 170°C to 65°C by conduction during the 5–7 km of lateral flow to the hot springs. 相似文献
9.
UPb geochronology provides an absolute time framework for the evolution of the Sigma gold deposit and surrounding rocks at Val d'Or, southern Abitibi subprovince. The Bourlamaque batholith, the largest pluton in the area, gives a 2699.8 ± 1.0 Ma UPb zircon age. This pluton cuts the Val d'Or Formation which hosts the mineralization. A UPb zircon age of 2704.9 ± 1.1 Ma on a felsic volcanic rock, the Colombière “rhyolite”, 13 km east of the mine dates that formation. The gold-bearing quartz vein system at Sigma is hosted by andesites and two generations of porphyry intrusions, all metamorphosed to the greenschist facies. The oldest porphyry (“porphyritic diorite”) shows the same deformation as the volcanic rocks, and has a 2703.7 ± 2.5 Ma UPb zircon age. The porphyritic diorite and volcanic rocks are cut by feldspar-porphyry dykes which post-date regional folding and have a 2694.0 ± 2.2 Ma UPb zircon age.Regional greenschist metamorphism has been dated directly, with a UPb date of 2684 ± 7 Ma on rutile in the Colombière “rhyolite”. The mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals. Hydrothermal rutile, from an alteration halo around the veins in andesite, has a 2599 ± 9 Ma UPb age. Textural evidence clearly indicates that the wall-rock alteration and vein filling are contemporaneous, and hence the vein system and gold mineralization appear to have developed at least 80 m.y. after the formation and metamorphism of host greenstones. 相似文献
10.
Least-squares collocation technique was used to process regional gravity data of the SE South American lithospheric plate in order to map intermediate (10–2000 km) wavelength geoid anomalies. The area between 35–10° S and 60–25° W includes the Paraná CFB Province, the Southern São Francisco Craton and its marginal fold/thrust belts, the Brazilian continental margin and oceanic basins. The main features in the geoid anomaly map are: (a) Paraná CFB Province is characterized by a 1000 km long and 500 km wide, NE-trending, 9 m-amplitude negative anomaly which correlates with the distribution of sediments and basalts within the Paraná basin. (b) A circular (600–800 km in diameter) positive, 8 m-amplitude geoid anomaly is located in the southern S. Francisco craton and extends into the northeastern border of the Paraná CFB Province. This anomaly partially correlates with Alto Paranaíba Igneous Province (APIP), where alkalic volcanism and tholeiitic dikes of ages younger than 80 Ma are found and where a low-velocity zone in the mantle has been mapped using seismic tomography. This positive geoid anomaly extends towards the continental margin at latitude 21° S and joins a linear sequence of short wavelength positive geoid anomalies associated with Vitoria–Trindade seamounts. (c) A NE-trending, 1000 km long and 800 km wide, 4 m-amplitude, positive geoid anomaly, which is located along the southeastern coast of Brazil, from latitude 24 to 35° S. The northern part of this anomaly correlates with the Ponta Grossa Arch and Florianopolis dyke swarm provinces. The age of this intrusive volcanism is 130–120 Ma. (d) A circular positive anomaly with 9 m of amplitude, located over the Rio Grande and Uruguay shields and offshore Pelotas basin. Few alkaline intrusives with ages between 65 and 80 Ma are found in the region and apatite fission track ages in basement rocks indicates cooling at around 30 Ma. A semi-quantitative analysis of the observed geoid anomalies using isostatic considerations suggests that the mechanism which generated Paraná CFB Province did not change, in a significant manner, the lithospheric thermal structure, since the same geoid pattern observed within this province continues northward over the Neoproterozoic fold/thrust belts systems separating the São Francisco and Amazon cratons. Therefore, this observation favours Anderson’s idea of rapid basaltic outpouring through a pull-apart mechanism along a major suture zone. A thermal component may still be present in the Southern São Francisco Craton and in the Rio Grande Shield and contiguous continental margins, sites of Tertiary thermal and magmatic reactivations. 相似文献
11.
IDOAS: A new monitoring technique to study the 2D distribution of volcanic gas emissions 总被引：1，自引：0，他引：1
N. Bobrowski G. Hnninger F. Lohberger U. Platt 《Journal of Volcanology and Geothermal Research》2006,150(4):329-338
Imaging Differential Optical Absorption Spectroscopy (IDOAS) is an optical remote-sensing method using scattered sunlight as light source. It combines a “pushbroom” imaging spectrometer with the DOAS technique and thus allows imaging two-dimensional trace gas distributions, e.g., in volcanic plumes. The highly sensitive and specific detection of many trace gases simultaneously (specific molecules, not just elements, e.g. SO2, BrO, NO2, O3, HCHO, etc.) is possible, and the temporal and spatial variation of these gases can be measured. The IDOAS system presented here enables the taking of two-dimensional images of trace gas distributions in a volcanic plume with a spatial resolution of 100 pixels horizontally × 64 pixels vertically, each with a field of view of 0.087° in horizontal and 0.208° in vertical directions. Therefore, IDOAS provides useful information about the chemical composition and chemical variability in a volcanic plume and allows studying plume dispersal and chemical transformations. The technique was applied to map the SO2 distribution in the plume of Mt. Etna volcano for the first time in October 2003. 相似文献
12.
M. Schmutz P. Andrieux A. Bobachev J.P. Montoroi S. Nasri 《Journal of Applied Geophysics》2006,60(3-4):213-224
Azimuthal Resistivity Soundings (ARS), using the so-called “Arrow-type array” as proposed by Bolshakov et al. were carried out in Central Tunisia, together with azimuthal resistivity tomography, because of the known anisotropic behaviour of the nearly vertical formations.First, the developments designed by Bolshakov et al. are reviewed: they deal with the separation between the effects of anisotropy and of heterogeneities, the design of the Arrow-type array and the introduction of the azimuthal spectral analysis.Second, the main methodological results obtained near Gouazine Lake are presented: (1) the clear effect of a quasi-vertical contact and (2) the characterisation of the anisotropic substratum below a thin superficial layer in one site close to the axis of the valley: the strike direction (α = 50°N), and a rather high anisotropy coefficient (λ ≈ 4) are determined.And lastly two directions for further developments are suggested. 相似文献
13.
F. Ousadou L. Dorbath C. Dorbath M. A. Bounif H. Benhallou 《Journal of Seismology》2013,17(2):207-222
The October 27, 1985 Constantine earthquake of magnitude MS 5.9 (NEIC) although moderate is the strongest earthquake recorded in the eastern Tellian Atlas (northeast Algeria) since the beginning of instrumental seismology. The main shock locations given by different institutions are scattered and up to 10 km away northwest from the NE–SW 30 km long elongated aftershocks cloud localized by a dedicated temporary portable network. The focal mechanism indicates left-lateral strike-slip on an almost vertical fault with a small reverse component on the northwest dipping plane. This paper presents relocations of the main shock and aftershocks using TomoDD. One hundred thirty-eight individual focal mechanisms have been built allowing the determination of the stress tensor at different scales. A rupture model has been suggested, which explains the different observations of aftershock distribution and stress tensor rotation. 相似文献
14.
Yo-ichiro Otofuji Jun Kadoi Shoubu Funahara Fumiyuki Murata Xilan Zheng 《Earth and Planetary Science Letters》1991,107(2)
Forty-five samples have been collected at nine sites on the 42.5 Ma Quxu pluton (90°50′E, 29°20′N) in the Gangdese batholith. Westerly declination (D = −48°and−83°) is observed in primary magnetizations from two sites about 25 km from the Indus-Zangbo suture zone after thermal demagnetization. This direction is consistent with the westerly paleomagnetic directions of the crustal blocks in other areas along the Indus-Zangbo suture zone. The Quxu pluton of the Gangdese Belt was rotated in a “domino style” deformation process as a part of a long (840 km) and narrow (less than 100 km) deformed zone between the India-Eurasia continents associated with the collision of India since 42.5 Ma. The pluton, between 11 km and 14 km from the suture acquired the secondary magnetization (D = −28°and−39°) during a cataclastic metamorphic process at sometime during the ‘domino style’ deformation. The primary magnetization was completely destroyed in the pluton within 11 km of the suture during slow cooling at the uplift stage and was replaced by thermoviscous remanent magnetization parallel to the present axial dipole field. 相似文献
15.
The Guadalentín Depression, located in SE Spain (Murcia Region), is bounded by two of the main NE-SW master faults of the Eastern Betics Cordilleras: The Lorca-Alhama and the Palomares left-lateral strike-slip faults. Available earthquake data indicate that, in the last 600 years, some sectors of the Lorca-Alhama Fault and the entire sector of the Palomares Fault have not been associated with significant historical seismicity. However, they show a wide range of diagnostic features of earthquake surface displacements on late Pleistocene and Holocene alluvial and colluvial surfaces. Aside from the left-lateral offsets recorded along 045–050 ° master fault strands of the Lorca-Alhama Fault, major paleoseismic surface displacements show different kinematics in relation to the broad orientation of the fault strands: (1) vertical normal displacements along 010–020 ° trending faults mainly preserved as degraded fault scarps of 2.5-1.8 m high (Aljibejo site); and (2) vertical reverse displacements, with average offsets of 0.2 – 1 m, along 065–080 ° subsidiary faults. In this last group, the younger one (Carraclaca Baths site) remains as a fault scarp of 0.8 m height affecting a cascade tufa which was active until the Spanish Roman Period (2nd Century B.C. to 6th Century A.D.). In other cases, reverse offsets resulted in smaller displacements (0.26 m) of paleosols, but show a recurrent behaviour (La Escarihuela site). The strongest earthquakes recorded in the study area did not exceed more than Mb 4.5 or MSK Intensity VIII (historical) with no evidence of coseismic rupture. Therefore, the preliminary data presented here seem to indicate that the paleoseismic activity on both faults is capable of producing coseismic surface displacements, probably reaching magnitudes of at least 6.5. These data show that paleoseismic studies based on geomorphological analyses are a useful tool in the assessment of the relative degree of activity of apparently ‘aseismic’ fault traces. 相似文献
16.
17.
B.R Clemesha D.M Simonich P.P Batista I.S Batista 《Journal of Atmospheric and Solar》1998,60(18):1773-1778
Lidar measurements of upper atmospheric sodium were made at Alcântara (2°20′ S, 44°30′ W), Brazil, on 8 days during the month of November 1996. These are the first sodium measurements to be reported from an almost equatorial location. The average sodium distribution at Alcântara was found to be very similar to the annual mean for São José dos Campos (23° S), but about 1 km higher than the November mean value of 92 km for the latter site. Only one, weak, sporadic sodium layer was observed during more than 26 h of observations, an occurrence frequency much less than that seen at low latitude sites in the northern hemisphere. A survey of the observations of sporadic layers at various locations suggests that both magnetic dip and declination angles might influence their rate of occurrence. 相似文献
18.
A study of emplacement temperatures was carried out for the largest of the 22 November 1994 nuée ardente deposits at Merapi Volcano, based mainly on the response of plastic and woody materials subjected to the hot pyroclastic current and the deposits, and to some extent on eyewitness observations. The study emphasizes the Turgo–Kaliurang area in the distal part of the area affected by the nuée ardente, where nearly 100 casualties occurred. The term nuée ardente as used here includes channeled block-and-ash flows, and associated ash-clouds of surge and fallout origins. The emplacement temperature of the 8 m thick channeled block-and-ash deposit was relatively high, 550°C, based mainly on eyewitness reports of visual thermal radiance. Emplacement temperatures for ash-cloud deposits a few cm thick were deduced from polymer objects collected at Turgo and Kaliurang. Most polymers do not display a sharp melting range, but polyethylene terephthalate used in water bottles melts between 245 and 265°C, and parts of the bottles that had been deformed during fabrication molding turn a milky color at 200°C. The experimental evidence suggests that deposits in the Turgo area briefly achieved a maximum temperature near 300°C, whereas those near Kaliurang were <200°C. Maximum ash deposit temperatures occurred in fallout with a local source in the channeled block-and-ash flow of the Boyong river valley; the surge deposit was cooler (180°C) due to entrainment of cool air and soils, and tree singe-zone temperatures were around 100°C. 相似文献
19.
We present new paleomagnetic results from the well dated Miyako Cretaceous sediments (100–110 Ma) from Northeast Japan. These results, combined with those of Tosha [1], yield an in-situ characteristic directionD = 321°,I = 54.5° (α95 = 4.5°),N = 14 sites; reduced to a reference point at 40°N, 142°E). This direction is found to coincide with that of most older plutonic and sedimentary rocks of Devonian to lower Cretaceous age. It is also identical with the westerly pre-folding direction which is preserved in many Oligocene (20–40 Ma) formations from Northeast Japan [1,2]. In contrast, all recent formations (0–17 Ma) have been magnetized in the direction of the present axial dipole field. Only the Oligocene and Miocene results appear to be primary, or at least pre-folding. The Miyako sulfide-bearing sediments and lower Cretaceous (110–125 Ma) magnetite-bearing granites could either still bear a primary magnetization or be completely remagnetized by a low temperature chemical event. Evidence for such events is now found in many places, and as close as South Korea. Available data constrain the Oligo-Miocene history of Northeast Japan and indicate at least20/30° counterclockwise rotation with respect to mainland Asia during the opening of the Sea of Japan. On the other hand, the pre-40 Ma history of Northeast Japan is not well constrained and three models are proposed which are compatible with various interpretations of the data. None of them can presently document pro-Oligocene motion of Northeast Japan with respect to Asia. The most “economical” model implies widespread remagnetization. We conclude that, because of the scarcity of well tested primary magnetization directions, the classical bending of the Japanese Islands rests on weaker grounds than generally realized and that no pre-40 Ma apparent polar wander path of the Japanese Islands can safely be proposed. 相似文献
20.
A good knowledge of the spatial and temporal distribution of precipitation is required for streamflow forecasting with a mathematical model. Thus, an operational method for correcting and integrating radar and station data with a minimum of operator intervention is under development. A total of 297 CAPPI maps at a height of 2 km have been used, each map representing a 2 h accumulation for 43 rainy days in the summer of 1978.Preliminary results have shown that it is necessary to detect and correct ground clutter as well as echoes coming from anomalous propagation. Thus, an algorithm has been developed to do so. In order to obtain a better idea on the necessity of correcting those echoes and on the efficiency of the algorithm, estimations of the mean areal daily rainfalls on the basin calculated from station data, are compared to estimations computed from (a) raw radar data, (b) radar data corrected with a ground clutter mask, and (c) radar data corrected with the developed algorithm, before and after calibration with station data. Similar comparisons between measured streamflows and streamflows computed by the CEQUEAU model, are presented, except for raw radar data. Actual results show that the identification and correction algorithm behaves very satisfactorily and could permit the operational use of radar data with hydrological models. Moreover, the sensitivity of the calibration factor on the number of meteorological stations is studied. It is shown that a relatively small number of stations may be used to calibrate the radar data. However, this number should be greater for convective than for continuous rain.