ALBERT

Beschreibung: The use of stable isotopes as climate proxies is widely accepted for climate reconstruction. Re-establishing climate signals, e.g. temperature, from isotope values of biological materials requires some knowledge of the system’s response behaviour. The related problems are discussed in conjunction with stable isotopes of two different terrestrial archives: carbon isotope data of tree rings from southern Germany and oxygen isotope data of diatoms from Lake Holzmaar, Germany. Carbon isotope temperature coefficients (Δδ13C/ΔT) derived from tree rings were chosen as an example for non-linear transformation of environmental signals through biological systems explaining negative and positive temperature coefficients. Thin radial tree ring sections taken from tree rings of different species (poplar, beech and oak) show carbon isotope variations of up to 3‰ with a characteristic, annually recurring isotope pattern. This behaviour is discussed in view of time resolution, isotope signature conservation and the question of storage and remobilisation of photosynthates with time. For Lake Holzmaar it is shown that isotope proxy signals derived from diatoms may not be unambiguously translated into abiotic environmental forcing factors, such as for example temperature. Corresponding measurements reveal that the isotopic input signal varies considerably and nonlinearly with temperature.

Beschreibung: In this study, we present an interpretation of seismic refraction profiles from the PISCO 94 experiment in northern Chile. As the PISCO experiment was a combined active and passive seismological study, we also discuss results of the passive part in the context of the seismic refraction model. Previous seismic refraction and gravimetric studies indicate a maximum crustal thickness of about 70 km beneath the Pre- and Western Cordillera. The new seismic refraction data lead to a differentiated image of the Andean crust which shows strong varying characteristics. The crustal discontinuities (up to five are detected) dip from W to E. The upper crust has a thickness of 18 km (Precordillera) to 23 km (magmatic arc) underlain by the recent middle crust down to 35-45 km where the velocity increases to about 7 km/s at its base. This crustal level is interpreted as old continental lower crust and its base as blurred continental (paleo) Moho. Beneath the Precordillera, a strong discontinuity at 70 km depth with a velocity increase to about 8 km/s was detected, interpreted as the recent geophysical Moho. For the magmatic arc, this deep discontinuity could not be found by active seismic measurements. The tomographic models of the seismological studies, in general, confirm the seismic refraction results. Anomalously high vp/vs rations in the deeper part of the forearc indicate a hydrated mantle wedge consisting of serpentine and amphibole-bearing peridotite and the 70 km discontinuity is interpreted as the boundary between these two different stages of the hydrated mantle wedge. A zone of high attenuation (Qp) and high vp/vs ratios beneath the magmatic arc coincides with the low velocity zones and indicates partially molten rocks from a depth of 20 km down to the asthenospheric wedge.

Beschreibung: The Erzincan strike-slip earthquake of March 13, 1992 ruptured a section of the North Anatolian fault (NAF) at the northern margin of the Erzincan basin. The focal depth of about 10 km was less than given by ISC and NEIC. Erzincan and the surrounding villages were considerably damaged. In the Erzincan basin and in the neighbouring mountains a seismic network of ten stations was installed. It was operating continuously from March 21 through June 16, 1992. More than 3,000 aftershocks were recorded of which 505 could be located. The spectral parameters of 394 and the fault-plane solutions of 53 aftershocks were determined. For the given region the frequency dependent coda Q was derived as Qc = 122*f^0.68. The aftershock area increased with time, reflecting the process of stress redistribution. Some events clustered in the immediate vicinity of the town of Erzincan close to the epicentre of the main event and seem to trace the NAF. Their source mechanism is similar to that of the main event (strike slip). About 150 aftershocks clustered in the southeastern part of the Erzincan basin where a concentration of the events in a small volume of 5 x 5 x 3 km^3 was observed. The majority of fault-plane solutions available for these aftershocks showed a normal faulting mechanism with an east-west directed extension. Most of the aftershocks southeast of the basin clustered between two lineaments that were mapped by satellite images. The P-wave velocity below the Erzincan basin, derived from travel-time residual analysis, is lower compared to areas NE and SW of the basin. Three-dimensional stress modelling of the Erzincan region qualitatively explains the occurrence of the aftershocks southeast of the basin. The calculated displacement distribution which exhibits the north-westward motion of the basin and tension at its southeastern margin, caused by the Erzincan earthquake, is in agreement with derived fault-plane solutions.

Beschreibung: A striking feature of Russian long-range seismic refraction data from Peaceful Nuclear Explosions is the observation of a high-frequency teleseismic P(tief)n, phase, which travels with a group velocity of 8.0 km s(hoch)-1 out to distances of several thousands of kilometres. Modelling using the reflectivity method shows that this phase can be understood as the response of an upper mantle that contains random RMS velocity fluctuations of about ±4 per cent superimposed on a positive velocity gradient. This class of model explains the existence of the teleseismic P(tief) n, its high-frequency content and its coda length. A teleseismic P(tief)n can only be generated if velocity flucluations are strong enough to cause multiple scattering and occur on a subwavelength scale. Cross-correlation properties of P- and S-wave velocity fluctuations exert a substantial influence on the wavefield. A completely unexpected phase can be observed if the fluctuations are imposed on a negative gradient

Beschreibung: For repeat pass SAR interferometry, two precision orbit products from ESA (processed at GFZ/D-PAF, Oberpfaffenhofen) are available: ERS-1/2.ORB.PRC"s and ERS-1/2.ORB.PRL"s. The conversion of interferogram phases to absolute surface heights require a relative baseline accuracy of 5 cm or even better. In a case study, the preliminary (PRL) and precise (PRC) orbits are used to derive DEMs. The results are compared with existing DTMs. In the test area in Thuringia (Germany), corner reflectors allow an additional accuracy assessment. The impact of orbit uncertainties on D-INSAR deformation analysis is less critical and the PRC"s already fulfill the accuracy demands. This is demonstrated by an example from the Dead Sea transform zone in Israel.

Beschreibung: Combined geological, structural, petrological and radiometric investigations provide constraints for the polyphase Variscan tectonothermal evolution of the Pulo de Lobo Zone in SW Spain. First phase deformation structures are intensively overprinted and only preserved in microlithons of the second Variscan phase. As Late Devonian overstep sequences are undeformed by the first Variscan deformation, this phase can be dated around the Frasnian/Famennian boundary. It argues for an early accretion of the Pulo do Lobo Zone to the Ossa-Morena Zone which was terminated in the late Devonian. During the Early Carboniferous the Pulo do Lobo Zone was successively deformed and sandwiched inbetween the Ossa-Morena Zone and the South Portuguese Zone. Oblique convergence resulted in a prominent phase of transpression. This stage comprises the second and third Variscan deformation phase, both with SSW directed thrusting and left-lateral displacement. Synkinematic intrusions started to ascend contemporaneously. Their final emplacement occured between the second and third deformation phase, cooling of the intrusions outlasted the third Variscan phase. The regional metamorphism of the Pulo do Lobo Zone reaches in the basal units upper greenschist to lower amphibolite facies conditions. The metamorphism is connected with the second Variscan deformation phase. As it is closely associated with a wide-spread contact metamorphism, the Spanish part of the Pulo do Lobo Zone appears widely underlain by synkinematic intrusions. The timing of transpression in the Pulo do Lobo Zone can be constrained by 40Ar/39Ar and 87Rb/86Sr isotope dates of synkinematic intrusions which range between 337 Ma and 328 Ma. They are interpreted as cooling ages and can be related to microstructural observations in the contact aureole of the intrusives. According to this Variscan transpression. low-grade metamorphism and magmatism occured almost contemporaneously in the late Visean and was terminated by the end of the Early Carboniferous. The Variscan deformation of the Pulo do Lobo Zone ended with left-lateral movements along previously generated thrusts during the late Carboniferous.

Beschreibung: Abstract: A new experimental technique for the study of deformation processes in rocks in transmitted light under the microscope uses a modified sapphire anvil cell in which one of the sapphire anvils can be rotated and thus permit the deformation of a thin solid sample disc. The deformation can be observed during the experiment through the anvils using a polarizing microscope stage. The technique is applicable up to 450 Celsius degree and up to 2 GPa confining pressure in the central part of the sample.

Beschreibung: The Mecklenburg Lake District in Germany was used to verify MIDORI AVNIR"s potential for water quality assessment. By means of remote sensing, water quality can be assessed by estimating chlorophyll content. Chlorophyll shows spectral characteristics with relatively high reflectance in the green and near-infrared spectral region. Chlorophyll concentration is one parameter to estimate the trophic state of a lake and it can be related to the amount of algae in the water. Complementary data sets (CASI, AVNIR, IRS-1C PAN and LISS) and a spectral database acquired by a field spectrometer are available for the test site. In this study, AVNIR data are being evaluated regarding water quality. Relative chlorophyll concentration of the lakes is differentiated by techniques of linear spectral unmixing on atmospherically corrected data. Results are in accordance to field measurements. Even though it is not feasible to estimate absolute chorophyll concentration using only 4 wavebands, groups of lakes with different states of bioproduction can be differentiated.

Beschreibung: Short-period, three-component recordings of the seismic wave field of peaceful nuclear explosions recorded on deep seismic sounding profiles (Quartz and Ruby-I, collected in 1984 and 1988, respectively) in northern Russia are used to constrain the nature of the high-frequency teleseismic Pn phase, which can be observed for receiver distance of 〉3000 km. We suggest that this phase is caused by velocity fluctuations in the upper mantle acting as scatterers. To test this hypothesis and to determine the properties of the upper mantles scatterers, the elastic reflectivity method (one-dimensional isotropic models) was used to model the coda of the high-frequency teleseismic Pn phase. Both the observed data and the synthetic record sections were analyzed by examining the coda decay rates of the teleseismic Pn phase at 5 Hz. Synthetic seismograms are computed for different models based on the global model IASP91 with an added zone of randomly distributed velocity fluctuations (lamellae) just below the crust-mantle boundary. These models may be characterized by the thickness of the scattering layer L, the vertical heterogeneity correlation length a, and the heterogeneity standard deviation sigma. The numerical simulation of the wave propagation in these models generated a high-frequency teleseismic Pn. Comparing the coda decay rates of synthetic seismograms with the observation, we tried to constrain the properties of the velocity model containing fluctuations in the upper mantle, L, a and sigma. In the distance range of the uninterfered high-frequency teleseismic Pn phase beyond 1300 km, the coda decay rates for our best fitting model are similar to the observed ones. This model has a 75 km thick zone of scatterers below the Moho, containing lamellae with an average thickness of 2 km and a RMS velocity perturbation of 5%. The modeling results show also that two other possible models, the whispering gallery phase along the crust-mantle boundary and scattering in the lower crust, taken alone are not able to explain the coda properties of the high-frequency teleseismic Pn phase.

Beschreibung: Single zircons from two orthogneiss complexes, the 'Grey Gneiss' and 'Red Gneiss', the lowermost tectonic units in the Erzgebirge, were dated. The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism (approx 8 kbar/600-650 degrees C) are identifical in both gneiss units and distinguish these rocks from the Lusatian granitoids. They grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. -from Authors