Über Sedimentation und atektonische Verformung der Deckschicht auf Eiskegeln abschmelzender Gletscher

Ohne Zusammenfassung     

A geophysical survey of the Spitsbergen Margin and surrounding areas

New geophysical information including multichannel seismic profiling data obtained by the PGO Sevmorgeologia Ministry of Geology of the former USSR, Murmansk during 1984–1988 is discussed and interpreted in this study. The deep structure, sedimentary cover and stratigraphy of the Spitsbergen Continental Margin, considered to be a passive margin, i.e. divergent in the northern part and strike-slip in the western part, is described.Two genetically different types of plateaus on the continental margin, Yermak in the north and Spitsbergen (Vestnesa) in the west, have been identified.The entire extent of the continental slope of the northern part of the Spitsbergen Continental Margin in the Eurasia Basin is underlain by attenuated continental crust, while at the base of the Southwest Continental Margin, the oceanic crust along almost the entire extent is observed. The sedimentary cover, up to 10 km thick within the West Spitsbergen Continental Margin, is likewise observed. Within the North Spitsbergen Margin, however, it does not exceed 3.5 km in thickness.The extension and deposition within the West Spitsbergen Margin began in early Oligocene, while the rifting with accompanying sedimentation within the North Spitsbergen Continental Margin started probably in Early Cretaceous.     

Rural and urban livelihoods,social exclusion and social protection in sub-Saharan Africa

Abstract

This paper shows that with the decline of overall poverty, the concern for rising or persisting inequalities and the need for a transformative social protection, the capacity of countering social exclusion and promoting social justice also becomes increasingly relevant to urbanizing sub-Saharan Africa. It is argued that several parts of sub-Saharan Africa are likely to move towards pro-poor urbanization and show emerging changes in rural and urban livelihoods. Then, the practice of social protection programmes along the rural–urban continuum in sub-Saharan Africa is examined extensively in order to determine whether these practices align with emerging changes in livelihoods and tackle social exclusion in a transformative way. It is found that the livelihoods of the poor are enhanced and that social inclusion has increased. However, social protection’s adaptation to emerging changes in rural and urban livelihoods is still poor, and so is social protection’s capacity to tackle social exclusion in a transformative way. It is concluded that transformative social protection would require more structural interventions through empowering pressure on the state and innovative decentralization from the top.     

Spatial and temporal variations in minibasin geometry and evolution in salt tectonic provinces: Lower Congo Basin,offshore Angola

In passive margin salt basins, the distinct kinematic domains of thin‐skinned extension, translation and contraction exert important controls on minibasin evolution. However, the relationship between various salt minibasin geometries and kinematic domain evolution is not clear. In this study, we use a semi‐regional 3D seismic reflection dataset from the Lower Congo Basin, offshore Angola, to investigate the evolution of a network of minibasins and intervening salt walls during thin‐skinned, gravity‐driven salt flow. Widespread thin‐skinned extension occurred during the Cenomanian to Coniacian, accommodated by numerous distributed normal faults that are typically 5–10 km long and spaced 1–4 km across strike within the supra‐salt cover. Subsequently, during the Santonian–Paleocene, multiple, 10–25 km long, 5–7 km wide depocentres progressively grew and linked along strike to form elongate minibasins separated by salt walls of comparable lengths. Simultaneous with the development of the minibasins, thin‐skinned contractional deformation occurred in the southwestern downslope part of the study area, forming folds and thrusts that are up to 20 km long and have a wavelength of 2–4 km. The elongate minibasins evolved into turtle structures during the Eocene to Oligocene. From the Miocene onwards, contraction of the supra‐salt cover caused squeezing and uplift of the salt walls, further confining the minibasin depocentres. We find kinematic domains of extension, translation and contraction control the minibasin initiation and subsequent evolution. However, we also observe variations in minibasin geometries associated with along‐strike growth and linkage of depocentres. Neighbouring minibasins may have different subsidence rates and maturity leading to marked variations in their geometry. Additionally, migration of the contractional domain upslope and multiple phases of thin‐skinned salt tectonics further complicates the spatial variations in minibasin geometry and evolution. This study suggests that minibasin growth is more variable and complex than existing domain‐controlled models would suggest.     

Dynamic torsional response of an end bearing pile in saturated poroelastic medium

A comprehensive analytical solution is developed in this paper to investigate the torsional vibration of an end bearing pile embedded in a homogeneous poroelastic medium and subjected to a time-harmonic torsional loading. The poroelastic medium is modeled using Biot’s two-phased linear theory and the pile using one-dimensional elastic theory. By using the separation of variables technique, the torsional response of the soil layer is solved first. Then based on perfect contact between the pile and soil, the dynamic response of the pile is obtained in a closed form. Numerical results for torsional impedance of the soil layer are presented first to portray the influence of wave modes, slenderness ratio, pile–soil modulus ratio and poroelastic properties. A comparison with the plane strain theory is performed. The selected numerical results are obtained to analyze the influence of the major parameters on the torsional impedance at the level of the pile head. Finally, the dynamic torsional impedance of this study is compared with that for floating pile in elastic soil.     

Seismic source mechanism inversion from a linear array of receivers reveals non-double-couple seismic events induced by hydraulic fracturing in sedimentary formation

We developed a new method to invert source mechanisms of seismic events observed from a single (vertical or near vertical) array of receivers. This method was tested on a synthetic dataset and applied to a seismic dataset acquired during hydraulic fracturing of a sedimentary formation. We show that a crack-opening seismic event recorded on a single vertical array can be inverted as a pure shear seismic event, indicating that the best fitting shear mechanisms inverted from seismic data acquired along a vertical borehole provide misleading information. We found that the majority of the analyzed source mechanisms of the induced events are not consistent with pure shear faulting as previously thought. The non-shear source mechanisms are required even when seismic noise, location uncertainty, and uncertainty in the attenuation structural model are considered.     

Air–Sea/Land Interaction in the Coastal Zone

Atmospheric turbulence measurements made at the U.S. Army Corps of Engineers Field Research Facility (FRF) located on the Atlantic coast near the town of Duck, North Carolina during the CASPER-East Program (October–November 2015) are used to study air–sea/land coupling in the FRF coastal zone. Turbulence and mean meteorological data were collected at multiple levels (up to four) on three towers deployed at different landward distances from the shoreline, with a fourth tower located at the end of a 560-m-long FRF pier. The data enable comparison of turbulent fluxes and other statistics, as well as investigations of surface-layer scaling for different footprints, including relatively smooth sea-surface conditions and aerodynamically rough dry inland areas. Both stable and unstable stratifications were observed. The drag coefficient and diurnal variation of the sensible heat flux are found to be indicators for disparate surface footprints. The drag coefficient over the land footprint is significantly greater, by as much as an order of magnitude, compared with that over the smooth sea-surface footprint. For onshore flow, the internal boundary layer in the coastal zone was either stable or (mostly) unstable, and varied dramatically at the land-surface discontinuity. The offshore flow of generally warm air over the cooler sea surface produced a stable internal boundary layer over the ocean surface downstream from the coast. While the coastal inhomogeneities violate the assumptions underlying Monin–Obukhov similarity theory (MOST), any deviations from MOST are less profound for the scaled standard deviations and the dissipation rate over both water and land, as well as for stable and unstable conditions. Observations, however, show a poor correspondence with MOST for the flux-profile relationships. Suitably-averaged, non-dimensional profiles of wind speed and temperature vary significantly among the different flux towers and observation levels, with high data scatter. Overall, the statistical dependence of the vertical gradients of scaled wind speed and temperature on the Monin–Obukhov stability parameter in the coastal area is weak, if not non-existent.     

Thermal reservoir modeling in petroleum geomechanics

Thermal oil recovery processes involve high pressures and temperatures, leading to large volume changes and induced stresses. These cannot be handled by traditional reservoir simulation because it does not consider coupled geomechanics effects. In this paper we present a fully coupled, thermal half‐space model using a hybrid DDFEM method. A finite element method (FEM) solution is adopted for the reservoir and the surrounding thermally affected zone, and a displacement discontinuity method is used for the surrounding elastic, non‐thermal zone. This approach analyzes stress, pressure, temperature and volume change in the reservoir; it also provides stresses and displacements around the reservoir (including transient ground surface movements) in a natural manner without introducing extra spatial discretization outside the FEM zone. To overcome spurious spatial temperature oscillations in the convection‐dominated thermal advection–diffusion problem, we place the transient problem into an advection–diffusion–reaction problem framework, which is then efficiently addressed by a stabilized finite element approach, the subgrid‐scale/gradient subgrid‐scale method. Copyright © 2008 John Wiley & Sons, Ltd.     

HIV and AIDS in Africa: a geographic analysis at multiple spatial scales

This study offers an alternative method rooted in GIS techniques and spatial analysis to estimate HIV/AIDS prevalence over space from an incomplete surveillance data set and explain the variation of those estimates. The results clearly show that the HIV/AIDS epidemic is complex and that it is interconnected with other geographic, historical, economic and cultural phenomena which help explain its spatial spread and variation. The regression models which were developed in this paper illustrated that variables which measure the historical context of colonialism such as resource exploitation and labor migration, gender, culture, contemporary global forces, poverty and disease burden have all contributed variously to the rapid spread of this disease both in space and time. The policy implication is that concentrating on behavior change or therapy alone may not turn the epidemic around. The attack needs to be multifaceted and interdisciplinary taking into consideration the context and the economic and social realities at multiple spatial scales.