ALBERT

Description: In this report, we will present the complete derivation of analytical expressions of the EM coupling torque in dependence on the parameters of the fields contributing to it. For this, we choose a special set of spherically harmonic (SH) base functions and present all major steps of the derivation. Our report will be (i) closer to a lecture note than to a scientific paper and should give all readers the possibility to follow the derivations with the related details in the appendix, and can be (ii) used as a formulary for scientists working on this special field of investigation.

Description: For the motivation behind our investigations, we refer to the introduction of the first part of our report, Hagedoorn & Geiner-Mai (2008). In this part, we will (i) give an analytical description of the topographic surface of the core-mantle boundary (CMB) and derive an approximation for its normal unit vector containing information about the CMB topography, and (ii) derive an expression for the topographic torque as a function of the topographic height, h, and the velocity field, u. For this, we will check the assumptions made when applying the geostrophic approximation to the upper core-surface region. Finally, we will derive analytical expressions for the torque components depending upon the spherical harmonic (SH) coefficients of h and u in a cartesian geocentric coordinate system.

Description: This volume contains extended abstracts from talks and posters presented at the sixth TRACE (Tree Rings in Archaeology, Climatology and Ecology) conference, held in Riga (Latvia) May 3rd – 6th, 2007.

Description: In this study two aspects of the geomagnetic field have been investigated. The first part focuses on perturbations of the external field, as seen by the CHAMP satellite and predicted by the Thermosphere-Ionosphere Electrodynamic General Circulation Model, for the purpose of helping to separate out ionospheric sources from the ambient geomagnetic field using a physics based approach. Part two looks at variations of the internal field through an examination of the South Atlantic Anomaly.

Description: The dynamic oblateness of the Earth, in terms of the J2 or C20 coefficient of the Earth´s geo-potential has been derived by analysis of LAGEOS Satellite Laser Ranging (SLR) data. Although recent analyses of GRACE (Gravity Recovery and Climate Experiment) mission data of monthly C20 values since 2002 have shown high temporal correlations with LAGEOS results, significant differences still remain. As it is common practice in GRACE data processing to remove a priori the short-term nontidal atmospheric and oceanic induced variations of the gravity potential via the socalled Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products, their use for LAGEOS data processing would allow a direct comparison of results and a rigorous combination of the solutions. Since the consideration of short-term non-tidal atmospheric and oceanic mass redistributions by means of AOD1B time series reveals a significant impact on LAGEOS data processing results, the AOD1B time series has been consistently prolongated back to the advent of LAGEOS-1 in 1976. An analysis for the period 1993-2006 leads to the major findings that the consideration of atmospheric and oceanic mass redistributions result in a considerably reduced seasonal signal in the LAGEOS C20 time series. This in turn reduces the correlation to GRACE significantly by about 30%. This is in opposite to what one would expect, i.e., a better agreement between GRACE and LAGEOS if common standards are applied. Thus, a LAGEOS solution corrected for short-term non-tidal atmosphere and ocean effects is much less sensitive to primarily annual hydrological mass variations than GRACE. In addition, significant semi-annual signals remain. Other indicators such as the unresolved bias between LAGEOS and GRACE in the order of 2·10-10 or LAGEOS orbits and Satellite Laser Ranging (SLR) observation residuals are hardly affected by the AOD1B model.

Description: Although the development of passive margins has been extensively studied over a number of decades, significant questions remain on how mantle and crustal dynamics interact to generate the observed margin geometries. Here, the Orange Basin, located on the south-west African continental margin is investigated. The basin fill is considered to comprise a classic rift-drift passive margin sequence recording the break-up of Gondwana and subsequent opening of the South Atlantic Ocean. Based on interpreted seismic reflection data, a 3D geological model was first constructed. Subsequently, an isostatic calculation (Airy´s model) using a homogeneous middle and lower crust was applied to this geological model to determine the position of the Moho for an isostatically balanced system. Isostatic sensitivity tests were applied to the model, and their gravity response was validated against different crustal structures for the basin. The best-fit model requires dense, presumably mafic material in the middle and lower crust beneath the basin and an abrupt change to less dense material near the coast to reproduce the observed gravity field. The passive margin of the South Atlantic shows typical features of a rifted volcanic continental margin, encompassing seaward dipping reflectors, continental flood basalts and high-velocity/density lower crust at the continent-ocean transition, probably emplaced during initial seafloor spreading in the Early Cretaceous. The Springbok profile offshore western South Africa is a combined transect of reflection and refraction seismic data. This thesis addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives. The velocity modelling revealed a segmentation of the margin into three distinct parts of continental, transitional and oceanic crust. As observed at many volcanic margins, the lower crust is characterised by a zone of high velocities with up to 7.4 km/s. The conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities, found to be 3100 kg/m³. Both approaches identified the body to have a thickness of about 10 km. Yet, the gravity modelling predicted the transition between the high-density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal. Finally, isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced. The results imply isostatic equilibrium over large parts of the profile; smaller deviations are supposed to be compensated regionally. The calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension. Furthermore, results of a combined approach using subsidence analysis and basin history inversion models are presented. The outcome shows that a classical uniform stretching model does not account for the observed tectonic subsidence. Moreover, it is found that that the thermal and subsidence implications of underplating need to be considered. Another departure from the uniform stretching model is renewed sub-crustal stretching and linked to that uplift in the Cenozoic which is necessary to reproduce the observed phases of erosion and the present-day depth of the basin. The dimension of these events has been examined and quantified in terms of tectonic uplift and sub-crustal stretching. Based on these forward models the heat flow evolution is predicted not only for the available real wells but also for virtual wells over the entire study area. Finally, the hydrocarbon potential and the temperature evolution is presented and shown in combination with inferred maturation of the sediments for depth intervals which comprise potential source rocks.

Description: This study is aimed at a development of numerical method to model the dynamic geoid and the surface plate velocities induced by global mantle flow with the effect of strong lateral viscosity variations (LVV) in conjunction with the effects of selfgravitation and mantle compressibility. I employ the technique, which comprises the combination of the spherical harmonic method, the direct Godunov method used for solving the Stokes and Poisson equations in spherical harmonics with arbitrary boundary conditions, functions of density and radial viscosity, and the iterative method based on the principles suggested by Zhang and Christensen (1993) used for modeling the effect of LVV. The 3-D mantle viscosity model is based on the global seismic tomography model S20a converted to temperature variations. The maximum lateral viscosity contrast in the lithosphere-asthenosphere zone modeled reaches four orders of magnitude. It is found that the influence of LVV on the dynamic geoid is extremely significant: an alteration of the geoid figure due to LVV exceeds 45% of the maximum geoid undulations. The detailed analysis showed that the geoid is affected by both, strong LVV induced in the upper mantle and large-scale LVV induced in the lower mantle. According to the results of this study the separated effects of the upper- and lower-mantle LVV on the geoid figure are nearly additive with respect to the whole-mantle LVV and partly compensating with respect to each other. The mantle flows are strongly affected by LVV as well, especially by the long-wavelength viscosity variations in the lower mantle: global upwellings tend to intensify due to the effects of LVV, while downwellings become weaker. The alteration of the near-surface velocities reaches 30-40% in amplitude not only due to the LVV induced toroidal flow but also due to change in the spheroidal velocity component. I can conclude that the LVV presented in both, upper and lower mantle, play an important part in global modeling, therefore, an incorporation of 3-D viscosity structure into the next generation global dynamic models is a task of vital significance.

Description: The joint project TIPTEQ (from The Incoming Plate to mega-Thrust EarthQake processes) refers to an integrated approach in order to investigate the processes active in the seismogenic coupling zone at the southern Central Chilean margin and to validate their importance for both the initiation of mega-thrust earthquakes and the evolution of the forearc. The lateral variability of these processes and related parameters is investigated along five marine corridors offshore the south Chilean continental margin. The northernmost marine transect is continued onshore with a reflection seismic survey at 38.2◦ S which crosses the hypocenter of the largest ever recorded earthquake, the 1960 Great Chilean earthquake (Mw = 9.5). The processing and structural interpretation of this high-resolution seismic data set is one major task of this thesis. Furthermore, a first-break tomography was conducted to construct a near-surface velocity model. Several tests to validate the tomographic images were conducted and the limitations of the data set and method were explored in detail. The reflection seismic transect lies in the center of an extensive geophysical program comprising magnetotelluric surveys and a large seismological network. An integrative interpretation with the results of the other geophysical groups of TIPTEQ concludes the thesis. The depth section of the TIPTEQ NVR data set shows the subducting Nasca plate below the segmented forearc and a highly reflective overriding South American plate down to a depth of 60 km. High reflectivity directly above the plate interface suggested to be associated with the existence of a subduction channel with a varying thickness of 2 - 5 km down to a depth of at least 38 km. It might continue towards depth. Local seismicity possibly defines the upper bound of the subduction channel. The continental Moho is not clearly imaged. However, one possible location is at 38 - 40 km depth given by the 1960 earthquake hypocenter. The Moho may be continued eastwards to a depth of 35 km where a prominent structure is imaged. This reflector coincides with the modeled Moho interface from a 3–D density model along the Chilean margin. The reflectivity east and above of the 1960 hypocenter area may exhibit alternative eastward continuations of the continental Moho. The position and extent of the continental mantle wedge changes accordingly. Major forearc features such as the crustal Lanalhue Fault Zone and a strong west-dipping reflector perpendicular to the plate interface can be observed. The reflectivity of the oceanic crust increases in depths below 35 km. This increase might be caused by fluid release due to the porosity collapse in basalt. The integrative interpretation links this observation with a zone of high Vp/Vs ratio calculated from the seismological velocity model. Combining all available data sets of seismological, magnetotelluric and gravimetrical findings results in a complex image of the southern Chilean subduction zone, which this thesis addresses to decode.

Description: [...] Studies regarding the theory of this correlation and how to handle it when estimating sub-daily polar motion together with nutation are included in the thesis. Furthermore, it is demonstrated that the common estimation of the terrestrial reference frame and EOPs can be employed to identify a mismatch between the local tie values and the estimated coordinate differences at co-located sites. Thus, the EOPs offer another independent evaluation of the LT values, as mentioned already above for the troposphere gradients. For the studies described in this thesis, it is of vital importance that continuous observations are available for all observation techniques. Therefore, the so-called CONT campaigns of the International VLBI Service for Geodesy and Astrometry (IVS) are well-suited. Such special campaigns with continuous VLBI observations for several days are initiated from time to time in order to demonstrate the full capabilities of VLBI. The studies described in the thesis at hand are based on the two-week CONT campaign scheduled in October 2002, named CONT02.

Description: This study presents methods and field experiments for ground-based GPS altimetry. Although Coarse/Acquisition Code (C/A-code) based methods are introduced, the main part of this work addresses the use of carrier phase-delay observations of the reflected GPS signal and focuses on specular reflection. [...] This study approves the feasibility of ground-based GPS altimetry with the OpenGPS receiver and with only one low-gain and wide field-of-view RHCP antenna using L1 carrier phase-delay observations of reflected GPS signals. The work shows the potential of GPS reflectometry for remote water level monitoring from a safe position in cases where in-situ measurements are not possible, are dangerous or sensors may get destroyed by the highly dynamic sea or glacier environment.

Description: The report contains a description of main results obtained within the research contract between IRE RAS and GFZ Potsdam and results of investigation during period November-December 2007 – the third stage of the contract. The objectives of investigation included (1) elaboration and verification of an innovative phase acceleration-refraction attenuation technique to locate layered and wave structures in the ionosphere and atmosphere; (2) elaborating of a new technique for identification of wave origin of temperature and density fluctuations and determination of the intrinsic frequency of internal gravity waves in the Earth's stratosphere from radio occultation (RO) data; presentation of a technique for evaluating the vertical profiles of the phase, amplitude, horizontal wind perturbations, intrinsic phase speed, kinetic and potential energy of atmospheric waves; (3) maps of waves parameters in the ionosphere and atmosphere showing their regional, seasonal and diurnal variations with aim to establish connections with solar and meteorological activity.

Description: This report studies the vertical crustal motion at tide gauges by analyzing GPS (Global Positioning System) height time series of about 370 GPS stations spanning 1994.0 to 2007.0. The procedure of generating a set of homogeneous GPS time series is described in detail. To estimate the vertical rate, the time series are modelled with seasonal (annual and semiannual) waves and step functions for jumps. To improve the quality of the time series, the ocean tide loading (OTL) corrections are renovated by replacing the OTL corrections derived from new ocean tides model directly on the solutions without re-analyzing the GPS data.

Description: The here presented study contributes to the understanding of convergent plate boundaries in the depth range of their former seismogenic zone aiming at testing inferences and hypotheses of the various kinematic and mechanical concepts presented for the seismogenic zone. Therefore, we use the complete exposure of this part of a former plate interface in the European Alps, one of the best-studied mountain belts that has resulted from successive subduction, accretion and collision, where we analyzed a mélange zone tracing the plate interface zone of the fossil convergent plate margin. Additionally, we included information from Southern Chile, where material, which formerly underwent deformation along the plate interface, was exhumed to the surface by large scale basal accretion at a certain depth to the base of the upper plate. This part of the study provided additive hints for structures and processes occurring along the plate interface zone of convergent plate margins (i.e. within the subduction channel), at least for a restricted PT domain.