Numerical modelling of airborne electromagnetic anomalies originating from low-conductivity 3D bodies1

Responses of a multifrequency, multicoil airborne electromagnetic (AEM) system were modelled numerically for 3D electrical conductors embedded in a resistive bedrock and overlain by an overburden of low to moderate conductivity. The results cover a horizontal coplanar coil configuration and two frequencies, 7837 Hz and 51 250 Hz. The models studied are single or multiple, poor conductors (conductance lower than 0.1 S) embedded in a host rock of high but finite resistivity (5000 Ωm) and overlain by a layer of overburden with finite thickness and low to moderate conductivity (conductance up to 2 S). On the basis of the modelling results, limits of detectability for poor conductors have been studied for the various model structures. The results indicate that the anomaly from a steeply dipping, plate-like conductor will decrease significantly when the conductor is embedded in a weakly conductive host rock and is overlain by a conductive overburden. However, an anomaly is obtained, and its magnitude can even increase with increasing overburden conductivity or frequency. The plate anomaly remains practically constant when only the overburden thickness is varied. Changes in overburden conductivity will cause the plate-anomaly values to change markedly. If the plate conductance is less than that of the overburden, a local anomaly opposite in sign to the normal type of anomaly will be recorded. Another major consequence is that conductors interpreted with free-space models will be heavily overestimated in depth or underestimated in conductance, if in reality induction and current channelling in the host rock and overburden make even a slight contribution to the anomalous EM field. The lateral resolution for the horizontal coplanar coil system was found to be about 1.7 times the sensor altitude. Similarly, the lateral extension of a horizontal conductive ribbon, required to reach the semi-infinite (half-space) behaviour, is more than three times the sensor altitude. Finally, screening of a steeply dipping plate, caused by a small, conductive horizontal ribbon, is much more severe than screening of the same plate by an extensive horizontal layer.     

东印度洋近20 ka以来的生物硅记录及其古生产力意义

通过对东印度洋钻孔CJ01-185的生物硅来探讨东印度洋古生产力的变化和古气候演化的响应。CJ01-185钻孔的生物硅含量在末次冰期最低,为0.86%;而到了全新世晚期生物硅含量达到1.89%。全新世晚期生物硅的堆积速率明显大于末次冰期。随着全新世海平面的快速上升,巽他海峡贯通,来自爪哇海的陆源物质输入到东印度洋,导致全新世的生物硅含量和生物硅的堆积速率增加。研究表明：巽他海峡贯通前,研究区的古生产力主要受东南季风变化和上升流的活动影响;而巽他海峡贯通后,古生产力很明显受到陆源物质输入的控制,东南季风变化和上升流的影响较弱。     

The lithosphere–asthenosphere boundary in the eastern part of the Dead Sea Basin (DSB) from S-to-P receiver functions

Clear S-to-P converted waves from the crust–mantle boundary (Moho) and lithosphere–asthenosphere boundary (LAB) have been observed on the eastern part of the Dead Sea Basin (DSB), and are used for the determination of the depth of the Moho and the LAB. A temporary network consisting of 18 seismic broad-band stations was operated in the DSB region as part of the DEad Sea Integrated REsearch project for 1.5 years beginning in September 2006. The obtained Moho depth (～35 km) from S-to-P receiver functions agrees well with the results from P-to-S receiver functions and other geophysical data. The thickness of the lithosphere on the eastern part of the DSB is about 75 km. The results obtained here support and confirm previous studies, based on xenolith data, geodynamic modeling, heat flow observations, and S-to-P receiver functions. Therefore, the lithosphere on the eastern part of the DSB and along Wadi Araba has been thinned in the Late Cenozoic, following rifting and spreading of the Red Sea. The thinning of the lithosphere occurred without a concomitant change in the crustal thickness and thus an upwelling of the asthenosphere in the study area is invoked as the cause of the lithosphere thinning.     

Dislocation structure of the crust-mantle boundary and low-velocity body within the crust beneath the Dabie Shan collision orogen

The Dabie Shan is located on the eastern side of the Qinling-Dabie orogenic belt, which marks a geological boundary between the Sino-Korean and Yangtze cra- ton. Since the 1980s, the discovery of coesite and mi- crodiamond in the Dabie Shan orogen motivates an extensive interest to the ultra-high pressure (UHP)metamorphism and its exhumation[1,2]. Many results about them were published, which deal with different disciplines, including tectonics, petrology and chro- nology[3?8]. Up to now,…     

A GPS-Based Online Control and Alarm System

A global positioning system (GPS)-based online control and alarm system (GOCA) for monitoring of three-dimensional movements has been developed at the Karlsruhe University of Technology. The GOCA hardware consists of an array of GPS sensors and communication units to be placed in the monitoring area. The hardware-dependent control software communicates with the GPS sensors and provides the GPS baseline data and covariance information to the GOCA deformation analysis software. The GOCA center, which comprises both the control software and the GOCA software, may be linked – for example, over a long distance – to another personal computer (PC) that serves as a remote control station. GOCA is able to provide the full capabilities of classical deformation analysis online (with stations grouped into stable points and moving object points). Both types of points may be occupied either continuously or over short periods at different times. The object points are determined with respect to the stable points. A network adjustment is performed for each interval of data collection, and the coordinate and covariance information may optionally be transformed into a specific reference system (e. g., the building system). Unstable reference points are to be detected by statistical tests. The estimated object point time series are filtered with respect to gross errors using robust estimation techniques. Online filters are used to smooth the time series data of critical displacements and to predict other deformation functions. The time series data, as well as prediction results, are displayed graphically for each object point. An example concerning the online monitoring of a slag heap in a coal-mining area is included. ? 2000 John Wiley & Sons, Inc.     

Study of inorganic ligand-chromium(III)-surface ternary complexes by ESR spectroscopy

Cr(III) sorbed at the solid/water interface of latex and hectorite was studied by ESR spectroscopy in the presence of different inorganic ligands. The ESR spectra of the surface obtained in the presence of selenite, phosphate and fluoride can be explained in terms of ternary surface complex formation. This is contrasted by the behaviour of sulfate and selenate ions which were found to have no effect on the ligand field of Cr(III), either in the adsorbed state or in solution.     

Functional feeding groups of a macroinvertebrate community in a northern German lake outlet (Lake Belau, Schleswig-Holstein)

At four typical sections of the stream Kossau Diptera were caught by emergence traps. Two of the sections can be regarded as to a great degree undisturbed due to their morphology and vegetation at the banks. Two sections have undergone various anthropogenic changes. Representatives of the families Chironomidae, Ceratopogonidae, Psychodidae, Limoniidae, Ptychopteridae, Dixidae, Culicidae, Simuliidae, and Empididae were collected. Altogether, 106 species were identified. The majority of species belong to the family Chironomidae (74), followed by the Ceratopogonidae (8), Psychodidae, and Empididae (7 each). The numbers of species collected at each stream section ranged from 56 to 69. At the undisturbed and shaded sections 69 and 66 species were found, at the meadow sections 56 and 68 species. Hence, a general connection between the loss of a state close to the natural environment and the number of species can not be stated.A total of 29,349 Diptera emerged. The highest number of individuals was found at a stream section covered with aquatic macrophytes (16,797 ind.), the lowest at a forest section without macrophytes (2,554 ind.). The Chironomidae make up for more than 82% of all Diptera. The Simuliidae rank second accounting for 3 to 17%, followed by the Ceratopogonidae. Like the Ceratopogonidae, all other families comprise less than 1% of the individuals collected.Only a few species demonstrated a distinct preference for the two forest sections of the stream, whereas about 50% of the species occurred in at least three of the four sections. Regarding the species represented by more than two individuals per emergence trap, it became apparent that the correspondence between the forst and the meadow sections is rather small.A comparison of the emergence of individual families revealed that many species found in the Kossau also occur in another lowland stream, similar to the Kossau concerning width, current velocity, and water level. Furthermore, the ecological demands of several species turned out to be not as high as they were considered to be, mainly referring to the temperature: Species proven in the Kossau and in other summer-warm streams may no longer be regarded as ‘cold-stenothermic’.