Die Bedeutung der Überschiebungen in Zentralasien

Ohne Zusammenfassung     

Das Pamir-System

Ohne Zusammenfassung     

Crooked line, rough topography: advancing towards the correct seismic image

Seismic exploration in mountainous areas imposes serious compromises on both acquisition and processing. Access restrictions usually result in profiles that are not straight and are not recorded along the true dip direction (if there is a true dip direction!). Processing constraints often result in very poor approximate corrections for elevations and for deviations from a straight line. Most fundamentally, 2D acquisition and processing assumes that the earth is 2D; this assumption is often seriously violated in mountainous areas. While we cannot efficiently correct 2D seismic data for the effects of a fully 3D subsurface, we can improve the data quality in thrust areas where the assumption of 2D subsurface variation is reasonable. We do this in a series of small steps, which improves the accuracy of several approximations made in processing 2D land data.     

Reconstruction of fluvio-lacustrine landscapes and settlement history in the Texcoco region,Mexico, using a modern geomorphic analog

Located in the Basin of Mexico, the eastern shore of former Lake Texcoco sustained a variety of human occupations throughout the Holocene, including preceramic hunter-gatherers, incipient agriculturalists, and a variety of settlements in the ceramic periods. Nonetheless, the environmental dynamics of occupations on the lakeshore have not been fully addressed. The Archaic preagricultural Texcoco Man site (>5000 B.C.E.) and the Late Formative TX-LF-14 site (c. 550-200 B.C.E.), among others, occupy this fluvio-lacustrine transitional environment. Few stratigraphic works in and around the sites have been performed. Consequently, it is difficult to understand the dynamics of the sedimentary system in space and time. This work highlights and describes the fluvio-lacustrine sedimentary dynamics and the resulting landscape that past societies inhabited on the eastern shore of Texcoco Lake. Because the study area has been altered by historic and modern draining, our work employs Lake Santiaguillo and its main tributary, the Tejamen River in the Durango state, as a modern analog to study their sedimentary dynamics. The analyses of surface geomorphology in the Texcoco study area were employed to corroborate the modern analog interpretation. To achieve these goals, we conducted a GIS-based morphometric analysis and LANDSAT-8 imagery to study the variations in landforms through wet and dry events. The results indicate an increase in the lake volume, low bifurcation in the active fluvial channels, few inundated surfaces, and the presence of bird-foot deltaic channels during high precipitation events. In contrast, low precipitation events are characterized by reduced lake volume, increased fluvial channel bifurcation, and expanded floodplains. This heterogeneous landscape thus provided a rich source of diverse natural resources of saline and freshwater aquatic habitats. Simultaneously, constant or recurring flooding events generated a challenging landscape for prehistoric settlers who implemented diverse technologies, such as the construction of tlateles, on the levees of deltaic channels to reduce the risk and impact of flooding events.     

Hydraulic properties of the crystalline basement

Hydraulic tests in boreholes, up to 4.5 km deep, drilled into continental crystalline basement revealed hydraulic conductivity (K) values that range over nine log-units from 10⁻¹³−10⁻⁴ m s⁻¹. However, K values for fractured basement to about 1 km depth are typically restricted to the range from 10⁻⁸ to 10⁻⁶ m s⁻¹. New data from an extended injection test at the KTB research site (part of the Continental Deep Drilling Program in Germany) at 4 km depth provide K=5 10⁻⁸ m s⁻¹. The summarized K-data show a very strong dependence on lithology and on the local deformation history of a particular area. In highly fractured regions, granite tends to be more pervious than gneiss. The fracture porosity is generally saturated with Na–Cl or Ca–Na–Cl type waters with salinities ranging from <1 to >100 g L⁻¹. The basement permeability is well within the conditions for advective fluid and heat transport. Consequently, fluid pressure is hydrostatic and a Darcy flow mechanism is possible to a great depth. Topography-related hydraulic gradients in moderately conductive basement may result in characteristic advective flow rates of up to 100 L a⁻¹ m⁻² and lead to significant advective heat and solute transfer in the upper brittle crust. An erratum to this article can be found at     

MAPPING FROM AN AUTOMATED DISPLAY SYSTEM*

This paper outlines recent developments in computer mapping and points out its importance for visualizing contents of geographic information systems. The authors present an integrated system of mapping packages and spatial-data files. Map examoles generated with this system are used to illustrate characteristics of various computer-mapping methods. The diversity of displays created from a single set of data demonstrates that mapping from automated display systems requires the user to take some decisions which have to be based on an understanding of the phenomena displayed, of cartographic communication, and of technical aspects of automated map processing.     

Optimized formulas for the gravitational field of a tesseroid

Various tasks in geodesy, geophysics, and related geosciences require precise information on the impact of mass distributions on gravity field-related quantities, such as the gravitational potential and its partial derivatives. Using forward modeling based on Newton’s integral, mass distributions are generally decomposed into regular elementary bodies. In classical approaches, prisms or point mass approximations are mostly utilized. Considering the effect of the sphericity of the Earth, alternative mass modeling methods based on tesseroid bodies (spherical prisms) should be taken into account, particularly in regional and global applications. Expressions for the gravitational field of a point mass are relatively simple when formulated in Cartesian coordinates. In the case of integrating over a tesseroid volume bounded by geocentric spherical coordinates, it will be shown that it is also beneficial to represent the integral kernel in terms of Cartesian coordinates. This considerably simplifies the determination of the tesseroid’s potential derivatives in comparison with previously published methodologies that make use of integral kernels expressed in spherical coordinates. Based on this idea, optimized formulas for the gravitational potential of a homogeneous tesseroid and its derivatives up to second-order are elaborated in this paper. These new formulas do not suffer from the polar singularity of the spherical coordinate system and can, therefore, be evaluated for any position on the globe. Since integrals over tesseroid volumes cannot be solved analytically, the numerical evaluation is achieved by means of expanding the integral kernel in a Taylor series with fourth-order error in the spatial coordinates of the integration point. As the structure of the Cartesian integral kernel is substantially simplified, Taylor coefficients can be represented in a compact and computationally attractive form. Thus, the use of the optimized tesseroid formulas particularly benefits from a significant decrease in computation time by about 45 % compared to previously used algorithms. In order to show the computational efficiency and to validate the mathematical derivations, the new tesseroid formulas are applied to two realistic numerical experiments and are compared to previously published tesseroid methods and the conventional prism approach.     

CLEAN: project overview on CO2 large-scale enhanced gas recovery in the Altmark natural gas field (Germany)

The joint research project CLEAN was conducted in the years 2008?C2011 by a German research and development (R&D) alliance of 16 partners from science and industry. The project was set-up as pilot project to investigate the processes relevant to enhanced gas recovery (EGR) by the injection of CO₂ into a subfield of the almost depleted Altmark natural gas field. Despite the setback that permission for active injection was not issued by the mining authority during the period of the project, important results fostering the understanding of processes linked with EGR were achieved. Work carried out led to a comprehensive evaluation of the EGR potential of the Altmark field and the Altensalzwedel subfield in particular. The calculated safety margins emphasize that technical well integrity of the 12 examined boreholes is given for EGR without a need for any further intervention. The laboratory and field tests confirm that the Altensalzwedel subfield is suitable for the injection of 100,000?t of CO₂. Numerical simulations provide sound predictions for the efficiency and safety of the EGR technology based on the CO₂ injection. The development and testing of different monitoring techniques facilitate an improved surveying of CO₂ storage sites in general. The CLEAN results provide the technological, logistic and conceptual prerequisites for implementing a CO₂-based EGR project in the Altmark and provide a benchmark for similar projects in the world.