Calculating the two-dimensional magnetotelluric Jacobian in finite elements using reciprocity   总被引：6，自引：0，他引：6  

Patricia Pastana de Lugão  Philip E. Wannamaker 《Geophysical Journal International》1996,127(3):806-810

To speed up the calculation of the field Jacobian for 2-D magnetoteliuric inversion using finite elements, the principle of electromagnetic reciprocity is applied. The governing relationship for the Jacobian of the field along strike is obtained by differentiating the Helmholtz equation with respect to the resistivity of each region in the finite-element mesh. The result is a similar Helmholtz equation for the Jacobian, with new sources distributed over all nodes within the parameter medium. However, according to the principle of electromagnetic reciprocity, the roles of sources and receivers are interchangeable. Utilizing reciprocity, the field values obtained from the original forward problem and for new unit sources imposed at the receivers are then utilized in the calculation of the Jacobian by simple multiplication and summation with finite-element terms at each rectangle in the mesh. For the auxiliary (across-strike) fields, the Jacobian terms are obtained by solving source vectors loaded with parabola coefficients used in the approximation to Maxwell's equations. Jacobian terms for the apparent resistivity ( p _a), the impedance phase (φ) and the vertical magnetic field ( K _zy) are then calculated utilizing the parallel- and auxiliary-field Jacobians. Comparison of Jacobian values obtained from reciprocity calculations and by differencing two forward solutions show that the reciprocity method is accurate and can be used to decrease the number of calculations required to obtain sensitivities by one to two orders of magnitude.  相似文献   

Petrologic studies of terrestrial organic matter in Carpathian flysch sediments, southern Poland     

Marian Wagner 《International Journal of Coal Geology》1996,29(4):259-272

In the Carpathian Flysch, coal is present either as exotics of Carboniferous coal deposits or as autochthonous, thin layers of lustrous coal. This paper present the results of the studies of coal-bearing rocks that are coeval with the enclosing flysch sediments. These coals form lenses up to 0.15 m thick. Their morphology precludes an exotic origin. The main petrographic component is collinite with admixtures of poorly fluorescing telinite. Minor components are: exudatinite, sporinite, fusinite, micrinite and sclerotinite. Mineral matter consists of framboidal pyrite clay minerals and quartz.The random reflectance of telocollinite varies from 0.38% to 0.72%, which corresponds to subbituminous and bituminous ranks. Correlation between chemical analysis, coking properties and relfectance measurements, leads to the conclusion that boundary between subbituminous and bituminous coals should be defined by the following values: C=80wt%, VOLATILES=43wt%; calorific VALUE=32.3 MJ/kg; and R^o=0.56–0.57%.Atypical properties, such as: upper C value (75–80wt%); high volatile matter contents (over 43wt%) and low random reflectance (^o about 0.38–0.57%) in subbituminous coals; low C value (about 80–82wt%); low reflectance (0.56–0.72%); and good coking properties, of the bituminous coals are attributed to quick coalification during increasing temperature as a result of tectonic stress.  相似文献   

The use of GPR and VES in delineating a contamination plume in a landfill site: a case study in SE Brazil   总被引：3，自引：0，他引：3  

Jorge L. Porsani  Walter M. Filho  Vagner R. Elis  Fisseha Shimeles  Joo C. Dourado  Helyelson P. Moura 《Journal of Applied Geophysics》2004,55(3-4):199-209

This paper presents the results of the application of the Ground Penetrating Radar (GPR) method, or Georadar, in outlining a zone of contamination due to solid residues at the waste burial site of Rio Claro in the state of São Paulo, SE Brazil. A total of eight GPR profiles with 50- and 100-MHz antennae were surveyed. Six profiles were located within the landfill site and the remaining two were outside. The main objective of the GPR survey was to evaluate the side extension of contamination. A Vertical Electric Sounding (VES) survey was performed at four points within the site in order to investigate the vertical extent of the contamination plume and to define the bottom of the landfill. Two additional VESs were done outside the landfill with the purpose of determining the top of the ground water table and the geoelectric stratigraphy of the background. From the interpretation of the GPR profiles, it was possible to locate the top of the contamination plume and to infer that it was migrating laterally beyond the limits of the waste disposal site. This was observed along the profile situated close to the highway SP-127, which was about 20 m from the limit of the site. The signature of the contaminant appears as a discontinuous reflector that is believed to be a shallow ground water table. The discontinuity is marked by a shadow zone, which is characteristic of conductive contaminant residues. The contamination did not move far enough to reach a sugar cane plantation located at approximately 100 m from the border of the site. In the regions free from contamination, the ground water table was mapped at approximately 10 m of depth, and it was characterized by a strong and continuous reflector. The radar signal penetrated deep enough and enabled the identification of a second reflector at approximately 14 m deep, interpreted as the contact between the Rio Claro and the Corumbataí formations. The contact is marked by the presence of gravel characterized by ferruginous concretes, which cause the strong amplitude reflection in the GPR profile. Within the landfill site, the quantitative interpretation of the VES results showed the contamination zone. The base of the landfill varies between 11 and 15 m deep. Outside the landfill site, the VES results showed no indication of contamination and allowed the determination of the top of the ground water table and the contact between the Rio Claro and the Corumbataí formations. The results of GPR and VES showed a good agreement and the integrated interpretations were supported by local geology and information from several boreholes, about 17 m depth, on average. The bottom of the landfill reaches a maximum of 14.5 m depth.  相似文献   

Assessing land use/cover changes: a nationwide multidate spatial database for Mexico     

Jean-Franois Mas  Alejandro Velzquez  Jos Reyes Díaz-Gallegos  Rafael Mayorga-Saucedo  Camilo Alcntara  Gerardo Bocco  Rutilio Castro  Tania Fernndez  Azucena Prez-Vega 《International Journal of Applied Earth Observation and Geoinformation》2004,5(4):249-261

A nationwide multidate GIS database was generated in order to carry out the quantification and spatial characterization of land use/cover changes (LUCC) in Mexico. Existing cartography on land use/cover at a 1:250,000 scale was revised to select compatible inputs regarding the scale, the classification scheme and the mapping method. Digital maps from three different dates (the late 1970s, 1993 and 2000) were revised, evaluated, corrected and integrated into a GIS database. In order to improve the reliability of the database, an attempt was made to assess the accuracy of the digitalisation procedure and to detect and correct unlikely changes due to thematic errors in the maps. Digital maps were overlaid in order to generate LUCC maps, transition matrices and to calculate rates of conversion. Based upon this database, rates of deforestation between 1976 and 2000 were evaluated as 0.25 and 0.76% per year for temperate and tropical forests, respectively.  相似文献   

Sedimentology and palynology of the Calafate Formation (Maastrichtian), Austral Basin, Southern Patagonia, Argentina     

S. Marenssi  V. Guler  S. Casadío  R. Guerstein  O. Papú 《Cretaceous Research》2004,25(6):907-918

The Calafate Formation crops out in south-western Santa Cruz Province, Argentina, and displays a stacking of asymmetrical coarsening–fining-upward cycles. These cycles are interpreted as the product of short-lived transgressive-regressive events in which the coarsening upward part represents sedimentary aggradation with a stable or decreasing sea level. Sedimentological and palynological analyses indicate nearshore marine conditions. Even though the existence of an estuary or incised valley cannot be determined, this is the most probable palaeogeographic model. Based on dinoflagellate cysts, the base of the section is considered to be not older than Maastrichtian. The presence of the oyster Ambigostrea clarae (Ihering) occurring together with the dinoflagellate cyst species Manumiella druggii (Stover) Bujak and Davies and Eisenackia circumtabulata Drugg in the middle part of the section indicates an age no older than late Maastrichtian. According to sedimentological data, deposits representing the Cretaceous–Palaeogene transition would have been eroded, which is confirmed by the presence of Grapnelispora loncochensis Papú. This megaspore is a consistent component of the Maastrichtian assemblages from Patagonia.  相似文献   

Seismic studies of the Brasília fold belt at the western border of the São Francisco Craton, Central Brazil, using receiver function, surface-wave dispersion and teleseismic tomography     

Marcelo Assumpo  Meijian An  Marcelo Bianchi  George S.L. Frana  Marcelo Rocha  Jos Roberto Barbosa  Jesús Berrocal 《Tectonophysics》2004,388(1-4):173

The Tocantins Province in Central Brazil is composed of a series of SSW–NNE trending terranes of mainly Proterozoic ages, which stabilized in the Neoproterozoic in the final collision between the Amazon and São Francisco cratons. No previous information on crustal seismic properties was available for this region. Several broadband stations were used to study the regional patterns of crustal and upper mantle structure, extending the results of a recent E–W seismic refraction profile. Receiver functions and surface wave dispersion showed a thin crust (33–37 km) in the Neoproterozoic Magmatic Arc terrane. High average crustal Vp/Vs ratios (1.74–1.76) were consistently observed in this unit. The foreland domain of the Brasília foldbelt, on the other hand, is characterized by thicker crust (42–43 km). Low Vp/Vs ratios (1.70–1.72) were observed in the low-grade foreland fold and thrust zone of the Brasília belt adjacent to the São Francisco craton. Teleseismic P-wave tomography shows that the lithospheric upper mantle has lower velocities beneath the Magmatic Arc and Goiás Massif compared with the foreland zone of the belt and São Francisco craton. The variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile. The integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the Goiás Massif and the foreland domain of the Brasília belt, whereas little variation was found across the foldbelt/craton surface boundary. These results support the hypothesis that the Brasília foreland domain and the São Francisco craton were part of a larger São Francisco-Congo continental plate in the final collision with the Amazon plate.  相似文献   

Intraplate seismicity in SE Brazil: stress concentration in lithospheric thin spots   总被引：1，自引：0，他引：1  

Marcelo Assumpção  Martin Schimmel  Christian Escalante  José Roberto Barbosa  Marcelo Rocha  Lucas V. Barros 《Geophysical Journal International》2004,159(1):390-399

  相似文献   

A constrained 2D gravity model of the Sebastián Vizcaíno Basin, Baja California Sur, Mexico     

J. García-Abdeslem  J.M. Romo  E. Gómez-Treviño  J. Ramírez-Hernández  F.J. Esparza-Hernández  C.F. Flores-Luna 《Geophysical Prospecting》2005,53(6):755-765

The subsurface geometry of the Sebastián Vizcaíno Basin is obtained from the 2D inversion of gravity data, constrained by a density-versus-depth relationship derived from an oil exploration deep hole. The basin accumulated a thick pile of marine sediments that evolved in the fore-arc region of the compressive margin prevalent along western North America during Mesozoic and Tertiary times. Our interpretation indicates that the sedimentary infill in the Sebastián Vizcaíno Basin reaches a maximum thickness of about 4 km at the centre of a relatively symmetric basin. At the location of the Suaro-1 hole, the depth to the basement derived from this work agrees with the drilled interface between calcareous and volcaniclastic members of the Alisitos Formation. A sensitivity analysis strongly suggests that the assumed density function leads to a nearly unique solution of the inverse problem.  相似文献   

Submillimeter-wave and observations of the event on 28 November, 2001     

G. Cristiani  G. Martínez  C.H. Mandrini  C.G. Gimnez de Castro  M.G. Rovira  P. Kaufmann  H. Levato 《Journal of Atmospheric and Solar》2005,67(17-18):1744

We present a detailed study of a 1B/M6.9 impulsive flare combining high time resolution (1 ms) and instantaneous emission source localization observations at submillimeter frequencies (212 GHz), obtained with the solar submillimeter telescope (SST), and Hα data from the Hα solar telescope for argentina (HASTA). The flare, starting at 16:34 UT, occurred in active region (AR) 9715 (NOAA number) on November 28, 2001, and was followed by an Hα surge. We complement our data with magnetograms from the Michelson Doppler Imager (SOHO/MDI). SST observed a short impulsive burst at 212 GHz, presenting a weak bulk emission (of about 90 sfu) composed of a few shorter duration structures. The integrated Hα and the 212 GHz light curves present a remarkable agreement during the impulsive phase of the event. The delay between both curves stays below 12 s (the time resolution of the Hα telescope). The flare as well as the surge are linked to new flux emergence very close to the main AR bipole. Taking into account the AR magnetic field evolution, we infer that magnetic field reconnection, occurring at low coronal levels, could have been at the origin of the flare; while in the case of surge this would happen at the chromospheric level.  相似文献   

Geomorphological and pedological investigations on the glacial history of the Kali Gandaki (Nepal Himalaya)     

Markus Wagner 《GeoJournal》2005,63(1-4):91-113

In semi-arid orographic left tributaries of the Kali Gandaki at the northern and western flank of the Nilgiri Himal, glacio-geomorphological and pedological investigations were carried out on prehistoric moraines. Geomorphological relief analysis was derived from other literature and the own fieldwork of the author. The resulting glacial chronology was used as benchmark to explore the limits of different pedological dating methods regarding the degree of soil development. These methods are based on iron fractionation, total element contents and particle size distribution. In general the different glacial stages are mirrored correctly in the relative graduation of soil development. The ratio of well crystallised pedogenic iron-oxides to the total iron content and the ratio fine clay to total clay are most suitable, because they are almost independent from existing changes in the lithological composition. The total element based weathering indices are less suitable, because they react highly sensitive to the geology dependent shift to higher carbonate content. Most of the grain size based weathering indices are inapplicable because of the typically high textural variability within till deposits.  相似文献