ALBERT

Beschreibung: An important question in geophysics is whether earthquakes (EQs) can be anticipated prior to their occurrence. Pre-seismic electromagnetic (EM) emissions provide a promising window through which the dynamics of EQ preparation can be investigated. However, the existence of precursory features in pre-seismic EM emissions is still debatable: in principle, it is difficult to prove associations between events separated in time, such as EQs and their EM precursors. The scope of this paper is the investigation of the pre-seismic EM activity in terms of complexity. A basic reason for our interest in complexity is the striking similarity in behavior close to irreversible phase transitions among systems that are otherwise quite different in nature. Interestingly, theoretical studies (Hopfield, 1994; Herz and Hopfield 1995; Rundle et al., 1995; Corral et al., 1997) suggest that the EQ dynamics at the final stage and neural seizure dynamics should have many similar features and can be analyzed within similar mathematical frameworks. Motivated by this hypothesis, we evaluate the capability of linear and non-linear techniques to extract common features from brain electrical activities and pre-seismic EM emissions predictive of epileptic seizures and EQs respectively. The results suggest that a unified theory may exist for the ways in which firing neurons and opening cracks organize themselves to produce a large crisis, while the preparation of an epileptic shock or a large EQ can be studied in terms of “Intermittent Criticality”.

Beschreibung: Numerous factors control the topographic evolution of mountain belts. Crustal thickening, rock uplift rate, and denudational forcing doubtlessly interact, but the feedback mechanisms amongst these are disputed, because they operate over entirely different time scales. Cosmogenically-derived denudation rates cover time-scales of 10(3) to 10(5) years, providing a denudational tool that allows us to shed light on interactions between long-term topography-forming processes and short-term factors destroying topography. Prerequisites for the application of this method in presently uplifting and fast-eroding mountain belts like the Central Alps are an investigation of appropriate watershed sizes for systematic sampling. Denudation rates in Maggia tributaries of various sizes reveal that the trunk stream yields statistically the same denudation rate (0.85 ± 0.14 mm/yr) as the tributaries (0.74 ± 0.14 mm/yr). Therefore, sampling of large watersheds is a feasible approach. Denudation rates of watersheds from the Central Alps are amongst the highest ever measured in similar complex settings, ranging in mean from 0.27 ± 0.05 mm/yr for the Alpine foreland to 1.42 ± 0.4 mm/yr for the high crystalline Central Alps. The measured cosmogenic denudation rates are in good agreement with post-LGM lake infill rates; they are significantly higher than recent denudation rates from river loads. We attribute this discrepancy to differences in methodology and integration time scale. We will show that denudation is high in areas of high altitude and high relief. Furthermore, our data shows that denudation rates are low in areas of low rock uplift, and are high in areas of high rock uplift, respectively. It appears that rock uplift and denudation are intimately linked. It follows that either crustal thickening is generating rock uplift; the mountain belt reacts with erosional unloading. Alternatively, high precipitation and glaciers, most pronounced at high altitude, result in high denudation rates at these sites. Topography then would respond by increasing rock uplift.

Beschreibung: The Aral Sea Basin is a critical area for studying the influence of climate and anthropogenic impact on the development of hydrographic conditions in an endorheic basin. We present organic-walled dinoflagellate cyst analyses with a sampling resolution of 15 to 20 years from a core retrieved at Chernyshov Bay in the NW Large Aral Sea (Kazakhstan). Cysts are present throughout, but species richness is low (seven taxa). The dominant morphotypes are Lingulodinium machaerophorum with varied process length and Impagidinium caspienense, a species recently described from the Caspian Sea. Subordinate species are Caspidinium rugosum, Romanodinium areolatum, Spiniferites cruciformis, cysts of Pentapharsodinium dalei, and round brownish protoperidiniacean cysts. The chlorococcalean algae Botryococcus and Pediastrum are taken to represent freshwater inflow into the Aral Sea. The data are used to reconstruct salinity as expressed in lake level changes during the past 2000 years. We quantify and date for the first time prominent salinity variations from the northern part of the Large Aral Sea. During high lake levels, I. caspienense, representing brackish conditions with salinities of about 10–15 g kg− 1 or less, prevails. Assemblages dominated by L. machaerophorum document lake lowstands during approximately 0–425 AD (or 100? BC–425 AD), 920–1230 AD, 1500 AD, 1600–1650 AD, 1800 AD and since the 1960s. Because salinity in the Aral Sea is mostly controlled by meltwater discharges from the Syr Darya and Amu Darya rivers, we interpret changes in salinity levels as a proxy for temperature fluctuations in the Tien Shan Mountains that control snow melt. Significant erosion of marine Palaeogene and Neogene deposits in the hinterland, evidenced between 1230 AD and 1400 AD, is regarded as sheet-wash from shore. This is controlled by the low pressure system that develops over the Eastern Mediterranean and brings moist air to the Middle East and Central Asia during late spring and summer. We propose that the recorded environmental changes are related primarily to climate, but perhaps to a lesser extent by human-controlled irrigation activities. Our results documenting climate change in western Central Asia are fairly consistent with reports elsewhere from Central Asia.

Beschreibung: The P and S seismic anomalies in the upper mantle beneath the Pamir–Hindukush collision zone and surrounding areas are investigated using more than 4 × 10 hoch 5 traveltimes from 5775 events located in the study region, recorded by the stations of the worldwide seismic network and reported in the ISC catalogue. All available epicentral distance ranges of seismic rays are considered. All sources are relocated using an algorithm, which includes the double-difference method. In addition, source parameters are corrected in the main inversion step, simultaneously with the velocity models. The high reliability of the resulting P-velocity images is confirmed by various tests. The S model provides much smoother patterns, which are, however, generally consistent with P anomalies. Our model shows a complex image of lithospheric plate under the study region. Under SW Hindukush, the northwards subducting Indian plate is imaged throughout the upper mantle and transition zone. Further to the NE, within a 300-km-wide zone the upper part of the plate overturns and then the slab breaks off after it narrows at ~250 km depth. The tomographic model also provides evidence for the southward subduction of the lithosphere beneath the southern Tien Shan down to at least 250 km depth. To the north of Tarim, we observe a northward-dipping of the Tarim plate down to ~500 km depth. At the crustal depth our model shows alternating belts of high and low velocities parallel to the main thrusting faults, which indicate complex crustal structure in this region.

Beschreibung: This paper presents results of geochemical investigations of lake sediments from the karst lake An Loch Mór, Aran Islands, including the first highly resolved record of atmospheric Roman Pb pollution for Ireland. The natural Pb influx into the lake is largely contributed by 3 Pb components, which differ in their isotopic composition: detrital influx of Pb from the siliciclastic input, dissolved influx of Pb released by weathering of the local limestone, and dissolved influx of seawater Pb. The balance between the 3 Pb components varies in concert with the hydrological evolution of the lake. The influx of Pb in dissolved form is estimated by geochemical mass balance assuming that the siliciclastic influx is characterised by the Pb/Al-ratio of the Late Glacial clastic sediments. It typically accounts for 50–80% of total Pb input in the Holocene sediments of An Loch Mór. The natural dissolved influxes of Pb, Sc, and Y reach a similar order of magnitude. Normalisation with Sc and Y is applied to quantify contributions from anthropogenic Pb. Based on continuous sampling of 1 cm sample slices, variations in the influx of Roman Pb could be reconstructed at a time resolution of c. 5 a. Combined geochemical and Pb isotope mass balance is used to characterise the isotopic composition of anthropogenic Pb. Distinctly enhanced influx of anthropogenic Pb occurs in the 1st and 2nd century AD and shows high variability on decadal scale. This is in contrast to central European Pb records, which document a gradual increase and decrease in ancient atmospheric pollution by Roman Pb. The reconstructed high variability in the influx of Roman Pb in An Loch Mór documents variations in the wind regime of western Europe, temporarily favouring the transport of atmospheric Pb to western Ireland.

Beschreibung: A high-resolution image of the base of the lithosphere from S-to-P converted seismic waves revealed the collision architecture of the Indian and Asian continental plates beneath the Tibetan Plateau. The base of the Indian lithosphere dips northward from a depth of 160 km beneath the Himalayas to a depth of 220 km just south of the Bangong suture. The base of the Asian lithosphere is nearly horizontal at the depth of 160–180 km from central to northern Tibet. There is a vertical gap of about 50 km between Indian and Asian lithospheres. Our observation of a well-defined, thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere, which would predict a very thin Asian lithosphere. The hypothesized sequential southward subduction of Tibetan and Asian continental lithospheres leading to the growth of the Tibetan Plateau, if correct, cannot be occurring below ∼180 km depth. Our results, along with available geological and geophysical data, strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted Indian continental lithosphere in the south, which presently can be traced to the middle of the plateau, and a south dipping subducted Asian lithosphere in the north at a shallower depth.

Beschreibung: The Potsdam Magnetic Model of the Earth (POMME) is a geomagnetic field model providing an estimate of the Earth's core, crustal, magnetospheric, and induced magnetic fields. The internal field is represented to spherical harmonic (SH) degree 90, while the secular variation and acceleration are given to SH degree 16. Static and time-varying magnetospheric fields are parameterized in Geocentric Solar-Magnetospheric (GSM) and Solar-Magnetic (SM) coordinates and include Disturbance Storm-Time (DSt index) and Interplanetary Magnetic field (IFM-By) dependent contributions. The model was estimated from five years of CHAMP satellite magnetic data. All measurements were corrected from ocean tidal induction and night-side ionospheric F-region currents. The model is validated using an independent model from a combined data set of Oersted and SACC-C satellite measurements. For the core field to SH degree 13, the root mean square (RSM) vector difference between the two models at the center of the model period is smaller than 4nT at the Earth's surface. The RMS uncertainty increases to about 100 nT for the predicted fields in 2010, as inferred from the difference between the two models.

Beschreibung: The uplift and evolution of a noncollisional orogen developed along a subduction zone, such as the Andean system, is a direct consequence of the interrelation between plate tectonic stresses and erosion. Tectonic stresses are related to the convergence velocity and thermal state, among other causes. In this paper, a new model designed to investigate the evolution of the topography and the upper crustal deformation of noncollisional orogens in a subduction zone produced by the oceanic crust being subducted is presented. The mechanical behavior of the crust was modeled by means of finite elements methods to solve Stokes equations for a strain-rate-dependent viscoplastic rheology. The model takes into account erosion effects using interface-tracking methods to assign fictitious properties to nonmaterial elements.

Beschreibung: A fully flexible ionic interaction model for alumina, Al2O3, is developed. The model accounts for ionic polarizability and shape deformations up to the quadrupolar level. The parameters of the interaction potential are optimized by reference to ab initio density-functional theory (DFT)-based electronic structure calculations. Two potential models, derived from DFT using the local density approximation (LDA) and the generalized gradient approximation (GGA), respectively are compared. Both potentials reproduce accurately bulk and surface properties of the corundum phase, and transfer well over a wide range of pressures and temperatures. The sequence of high pressure polymorphic phases is predicted correctly. The potential derived from LDA-DFT also gives an excellent description of the melt whereas the potential fitted to GGA-DFT considerably overestimates the equilibrium molar volume of the melt. The accuracy of the potentials regarding, e.g., lattice parameters or elastic constants is comparable to the respective electronic structure method.

Beschreibung: Unsere Erde ist von einem Magnetfeld umgeben, welches durch Vorgänge im Erdkern erzeugt wird, die wir nun im Großen und Ganzen verstehen. Das Erdmagnetfeld ist sowohl in der Stärke als auch in seiner Ausrichtung zeitlich variabel. Ziel unserer Arbeit ist es, die Veränderungen des Magnetfelds zu analysieren und Prognosen für seine zukünftige Entwicklung möglich zu machen.

Beschreibung: Knickpoints are a reliable indicator of stream channel incision. How these features impact a drainage basin as a whole as they migrate upstream however is less clear. To address this question, we have studied drainage basins in the Swiss Mitteland that have differing histories with respect to knickpoints and knickpoint migration. The Grosse Fontanne is a bedrock stream that drains the Molasse conglomerates of the Napf region. The system has been described as an actively incising rejuvenated landscape. Incised valleys and knickpoints are present on the trunk stream and many tributaries. Seven basinaveraged erosion rates varying from 330 to 640 mm/ky, derived from cosmogenic nuclides, were calculated for the watershed. The highest rates were recorded for the trunk stream near the confluence with the Kleine Emme River, while the lowest rates are found in small headwater basins. Of the samples, three were collected upstream of visible knickpoints, and two were collected downstream of visible knickpoints. The two remaining samples were collected on tributaries that had no visible knickpoints. The upstream erosion rates are lower, 350 mm/ky vs. 560 mm/ky, than the downstream erosion rates. The watersheds with no visible knickpoints are similar to the downstream samples, eroding at 500 mm/ky, suggesting that the knickpoint has already propagated through these catchments. The basins with active or presumed relict knickpoints also tend to have higher average relief than the basins which the knickpoints have not yet reached. The timing of initial formation, based on the volume of incision and a calculated erosion rate for the areas experiencing rapid downcutting, appears to be post-glacial. The cause of the knickpoint formation appears to be stream piracy by the Kleine Emme.

Beschreibung: The recent surge of applications using terrestrial cosmogenic nuclides (TCNs) to calculate catchment-averaged erosion rates from isotopic concentrations in fluvial sediment, and the prospect of coupling TCN production functions with numerical surface process models (SPMs), necessitate a fast and accurate algorithm for the calculation of topographic shielding. Topographic shielding refers to the proportion of the incoming cosmic radiation that is shielded by the surrounding topography, the scaling factor being defined as the ratio of the unshielded (total minus shielded) to the total (or maximum) cosmic ray flux (i.e. the flux received by a horizontal, unobstructed surface). Topography contributes to the reduction of TCN production by obstructing a certain proportion of the incoming flux and by modifying the angle of incidence. Available algorithms calculate the proportion of obstructed radiation by dividing the horizon as seen by the sample (a grid cell in the case of a DEM), into arc segments (usually of equal length) for which the average obstruction heights expressed as zenith angles are calculated. The use of these methods is feasible only when dealing with a small number of isolated samples, since the identification of obstructions when dealing with an entire area is computationally very intensive. This paper describes a method that uses a relief shadow modelling technique to identify those areas of a DEM that are under shadow (i.e. shielded), and thus to account for the obstructed radiation. This method produces results that are very similar to those obtained using a direct implementation of available methods (maximum difference between results of c. 0·1). The method based on relief shadow modelling is also faster than a direct implementation of any available method and can be readily implemented in any GIS system with raster capabilities.