Discrete wavenumber solutions to numerical wave propagation in piecewise heterogeneous media – I. Theory of two-dimensional SH case     

Li-Yun Fu  Michel Bouchon 《Geophysical Journal International》2004,157(2):481-498

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The Kaiserslautern multiscale geopotential model SWITCH-03 from orbit perturbations of the satellite CHAMP and its comparison to the models EGM96, UCPH2002_02_0.5, EIGEN-1s and EIGEN-2   总被引：2，自引：0，他引：2  

M. J. Fengler  W. Freeden  V. Michel 《Geophysical Journal International》2004,157(2):499-514

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垄行作物玉米方向亮温野外测量中视场角影响的简单分析   总被引：3，自引：4，他引：3  

余涛  顾行发  田国良  Michel Legran  Jean-Francois Hanocq  Roland Bosseno 《遥感学报》2004,8(5):443-450

基于透视原理、地面试验中对于较高目标的观测存在着一定的偏差。这种偏差随传感器高度、观测角度、视场角大小、观测位置等多个因素改变。由于垄行作物空间结构和温度分布的复杂性 ,在采用较大视场角测量方向亮温的地面实验中 ,将不可避免地存在着误差。采用一个简化的三分量二维结构模型对这种误差进行初步的分析与估算。亮温三分量分别为植被、被阳光照到的亮土和植被阴影下的暗土。作物的结构简化为剖面为矩形的无限长平行体。通过对这三个分量在传感器视场中面积权重的计算来模拟目标结构、传感器高度、位置、视场角大小、观测角度等因素对测量结果产生的影响。模拟结果表明 ,在垂直观测中 ,视场中的植被权重往往被高估 ,偏差随传感器高度的降低急剧增加。在倾斜观测中 ,由于一种互补效应的产生 ,偏差被限制在一个较低的范围内。经过分析 ,减小误差的最有效办法是提高传感器高度。最后 ,实验数据与模拟结果进行了比较。恰当地选取模型输入 ,两种数据能非常好的吻合。  相似文献   

Ubinas: the evolution of the historically most active volcano in southern Peru     

Jean-Claude Thouret  Marco Rivera  Gerhard Wörner  Marie-Christine Gerbe  Anthony Finizola  Michel Fornari  Katherine Gonzales 《Bulletin of Volcanology》2005,67(6):557-589

Ubinas volcano has had 23 degassing and ashfall episodes since A.D. 1550, making it the historically most active volcano in southern Peru. Based on fieldwork, on interpretation of aerial photographs and satellite images, and on radiometric ages, the eruptive history of Ubinas is divided into two major periods. Ubinas I (Middle Pleistocene >376 ka) is characterized by lava flow activity that formed the lower part of the edifice. This edifice collapsed and resulted in a debris-avalanche deposit distributed as far as 12 km downstream the Rio Ubinas. Non-welded ignimbrites were erupted subsequently and ponded to a thickness of 150 m as far as 7 km south of the summit. These eruptions probably left a small collapse caldera on the summit of Ubinas I. A 100-m-thick sequence of ash-and-pumice flow deposits followed, filling paleo-valleys 6 km from the summit. Ubinas II, 376 ky to present comprises several stages. The summit cone was built by andesite and dacite flows between 376 and 142 ky. A series of domes grew on the southern flank and the largest one was dated at 250 ky; block-and-ash flow deposits from these domes filled the upper Rio Ubinas valley 10 km to the south. The summit caldera was formed between 25 and 9.7 ky. Ash-flow deposits and two Plinian deposits reflect explosive eruptions of more differentiated magmas. A debris-avalanche deposit (about 1.2 km³) formed hummocks at the base of the 1,000-m-high, fractured and unstable south flank before 3.6 ka. Countless explosive events took place inside the summit caldera during the last 9.7 ky. The last Plinian eruption, dated A.D.1000–1160, produced an andesitic pumice-fall deposit, which achieved a thickness of 25 cm 40 km SE of the summit. Minor eruptions since then show phreatomagmatic characteristics and a wide range in composition (mafic to rhyolitic): the events reported since A.D. 1550 include many degassing episodes, four moderate (VEI 2–3) eruptions, and one VEI 3 eruption in A.D. 1667. Ubinas erupted high-K, calc-alkaline magmas (SiO₂=56 to 71%). Magmatic processes include fractional crystallization and mixing of deeply derived mafic andesites in a shallow magma chamber. Parent magmas have been relatively homogeneous through time but reflect variable conditions of deep-crustal assimilation, as shown in the large variations in Sr/Y and LREE/HREE. Depleted HREE and Y values in some lavas, mostly late mafic rocks, suggest contamination of magmas near the base of the >60-km-thick continental crust. The most recently erupted products (mostly scoria) show a wide range in composition and a trend towards more mafic magmas.Recent eruptions indicate that Ubinas poses a severe threat to at least 5,000 people living in the valley of the Rio Ubinas, and within a 15-km radius of the summit. The threat includes thick tephra falls, phreatomagmatic ejecta, failure of the unstable south flank with subsequent debris avalanches, rain-triggered lahars, and pyroclastic flows. Should Plinian eruptions of the size of the Holocene events recur at Ubinas, tephra fall would affect about one million people living in the Arequipa area 60 km west of the summit.Editorial responsibility: D Dingwell  相似文献   

A field test of imaging properties of rotational invariants of the magnetotelluric impedance tensor   总被引：1，自引：0，他引：1  

László Szarka  Antal Ádám  Michel Menvielle 《Geophysical Prospecting》2005,53(3):325-334

A part of the Békés Basin (an extensional sub‐basin of the Pannonian Basin, where the basement under thick Pannonian sediments is well known from deep boreholes and from seismic measurements, and where many magnetotelluric (MT) soundings have been carried out for frequencies ranging from 1 to 10^?3 Hz) was selected as a test area to assess the imaging performances of various apparent‐resistivity definitions computed with rotational invariants of either the real part of the complex impedance tensor, or its imaginary part, or both. A comparison (based on earlier 3D numerical studies) has been made between the magnetotelluric images obtained in this way and the depths to the high‐resistivity basement, as known from boreholes and seismic investigations. The correlation coefficient between the series of basement depth values at 39 MT sites and the apparent‐resistivity values was found to be stronger and high correlation appeared at a shorter period when it was computed with apparent resistivities based on the real tensor rather than with apparent resistivities based on the imaginary tensor. In the light of our studies, ρ_{Re Z} and the impedance phase seem to be more informative than any other combination of magnetotelluric interpretation parameters.  相似文献   

3D modelling and sensitivity in DC resistivity using charge density     

Olivier Boulanger  Michel Chouteau 《Geophysical Prospecting》2005,53(4):579-617

A three‐dimensional (3D) electrical resistivity modelling code is developed to interpret surface and subsurface data. Based on the integral equation, it calculates the charge density caused by conductivity gradients at each interface of the mesh, allowing the estimation of the potential everywhere without the need to interpolate between nodes. Modelling generates a huge matrix, made up of Green's functions, which is stored by using the method of pyramidal compression. The potential is compared with the analytical and the numerical solutions obtained by finite‐difference codes for two models: the two‐layer case and the vertical contact case. The integral method is more accurate around the source point and at the limits of the domain for the potential calculation using a pole‐pole array. A technique is proposed to calculate the sensitivity (Jacobian) and Hessian matrices in 3D. The sensitivity is based on the derivative with respect to the block conductivity of the potential computed using the integral equation; it is only necessary to compute the electrical field at the source location. A direct extension of this technique allows the determination of the second derivatives. The technique is compared with the analytical solutions and with the calculation of the sensitivity according to the method using the inner product of the current densities calculated at the source and receiver points. Results are very accurate when the Green's function that includes the source image is used. The calculation of the three components of the electric field on the interfaces of the mesh is carried out simultaneously and quickly, using matrix compression.  相似文献   

Modelling of Seepage Water Composition from Experiments with an Acid Soil and a Calcareous Sediment     

Kerstin Michel  Bernard Ludwig 《洁净——土壤、空气、水》2005,33(6):595-604

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The influence of H2O-H2 fluids and redox conditions on melting temperatures in the haplogranite system     

B. C. Schmidt  François Holtz  Bruno Scaillet  Michel Pichavant 《Contributions to Mineralogy and Petrology》1997,126(4):386-400

Solidus temperatures of quartz–alkali feldspar assemblages in the haplogranite system (Qz-Ab-Or) and subsystems in the presence of H₂O-H₂ fluids have been determined at 1, 2, 5 and 8 kbar vapour pressure to constrain the effects of redox conditions on phase relations in quartzofeldspathic assemblages. The hydrogen fugacity (f _H2) in the fluid phase has been controlled using the Shaw membrane technique for moderately reducing conditions (f _H2 < 60 bars) at 1 and 2 kbar total pressure. Solid oxygen buffer assemblages in double capsule experiments have been used to obtain more reducing conditions at 1 and 2 kbar and for all investigations at 5 and 8 kbar. The systems Qz-Or-H₂O-H₂ and Qz-Ab-H₂O-H₂ have only been investigated at moderately reducing conditions (1 and 5 kbar) and the system Qz-Ab-Or-H₂O-H₂ has been investigated at redox conditions down to IW (1 to 8 kbar). The results obtained for the water saturated solidi are in good agreement with those of previous studies. At a given pressure, the solidus temperature is found to be constant (within the experimental precision of ± 5°C) in the f _H2 range of 0–75 bars. At higher f _H2, generated by the oxygen buffers FeO-Fe₃O₄ (WM) and Fe-FeO (IW), the solidus temperatures increase with increasing H₂ content in the vapour phase. The solidus curves obtained at 2 and 5 kbar have similar shapes to those determined for the same quartz - alkali feldspar assemblages with H₂O-CO₂- or H₂O-N₂-bearing systems. This suggests that H₂ has the behaviour of an inert diluent of the fluid phase and that H₂ solubility in aluminosilicate melts is very low. The application of the results to geological relevant conditions [HM (hematite-magnetite) > f _O2 > WM] shows that increasing f _H2 produces a slight increase of the solidus temperatures (up to 30 °C) of quartz–alkali feldspar assemblages in the presence of H₂O-H₂ fluids between 1 and 5 kbar total pressure. Received: 4 March 1996 / Accepted: 22 August 1996  相似文献   

Secondary Ca–Al silicates in plutonic rocks: implications for their cooling history     

Regina Freiberger  Lutz Hecht  Michel Cuney  Giulio Morteani 《Contributions to Mineralogy and Petrology》2001,141(4):415-429

Secondary Ca-Al silicates are used to constrain the P-T-x conditions of the very early post-magmatic stage of the intermediate to basic Hercynian plutonic complexes of Charroux-Civray (NW Massif Central, France) and Fichtelgebirge (NE Bavaria, Germany). The secondary Ca-Al silicates hydrogarnet, prehnite, pumpellyite, epidote and laumontite form lenses within unaltered or only slightly chloritized biotite. Hydrogarnet as the first occurring Ca-Al silicate phase crystallizes at temperatures above 340 °C. The common paragenesis prehnite + pumpellyite post-dates hydrogarnet and indicates rather narrow ranges of temperature (200-280 °C) and pressure (2-3 kbar). Laumontite is formed at the end of Ca-Al silicate crystallization (180-260 °C, 1-3 kbar), mostly in small fractures in association with prehnite and adularia. The observed crystallization sequence of the Ca-Al silicates and their stabilities define a retrograde alteration path for the plutonic rocks. The Ca-Al silicate assemblage results from an early pervasive alteration of the plutonic rocks by low X_CO2 fluids during post-magmatic cooling. Subsolidus cooling starts at about 4 kbar at solidus temperatures as indicated by magmatic epidote stability, hornblende barometry and fluid inclusion data, and continues under slightly decreasing pressure (uplift) down to 2-3 kbar at 200-280 °C (prehnite-pumpellyite paragenesis). This shows that Ca-Al silicate assemblages may be a unique tool to constrain the P-T conditions of the subsolidus cooling of intermediate to basic plutonic bodies.  相似文献   

Brood patch temperature during provocation of common eiders in Ny-Ålesund, Svalbard     

Francois Criscuolo  Michel Gauthier-Clerc  Yvon Le  Maho Geir W. Gabrielsen 《Polar research》2001,20(1):115-118

In this short note we describe the behaviour and body changes of three incubating female common eiders ( Somateria mollissima ) during provocation made by humans approaching the nest. The study site was near the settlement of Ny-Ålesund, Svalbard. Temperture transmitters were implanted subcutaneously at the brood patch and data recorded using a VHF receiver. We found that the female experiment exhibited a passive defence response ("freezing"), accompanied by a significant drop in brood patch temperature (0.6 °C) during provocation; this temperature drop lasted for 5 minutes. These accord with other studies of the physiological changes which the passive defence response in birds and other animals.  相似文献