ALBERT

Beschreibung: The tables and graphs result from evaluation of Model 1 (see Veröffentlichungen des Zentralinstituts für Physik der Erde, Nr. 41, Potsdam 1976). They help to approximate values of the hydrostatic pressure P, the bulk modulus and its pressure derivative and the seismic parameter of a sample at any volume contraction x in the range between 0.5 and 1 if these quantities referred to the initial state (P = 0) are known. The considered functions are tabulated for a set of grid points of the rectangle 0.5 ≤ x ≤ 1, 2.1 ≤ ϰ_1 ≤ 10, where ϰ_1 is the initial value of the pressure derivative of the bulk modulus. The lattice pitchs are 0.01 in x and 0.1 in ϰ_1. The inverse problem can also be solved approximately with the aid of the tables and, above all, the plots presented here by using the "method of corresponding curves".

Beschreibung: Summary 1. Preface 2. Theoretical excursus 3. Some remarks on Model 1 4. Instructions for using tables and plots 5. References 6. Tables and figures

Beschreibung: Understanding the climate system and the natural processes that lead to its changes is fundamental when trying to evaluate and assess the human influence on climate variability. Human activities characterised most of the Holocene time period, so that palaeoclimate sequences of the last 8,000 years recorded both climate change and human impact. In order to study natural climate variability, we have to investigate past interglacial climate records, when human impact was none. Amongst many palaeoclimate archives, lacustrine varved sequences are invaluable records that allow high resolution palaeoclimate reconstruction. The interglacial lake deposits of Piànico (Southern Alps) consist of ca 15,500 biochemically precipitated calcite varves. The goal of my research is the sedimentological, geochemical and isotopical study at seasonal/decadal resolution of climate variability as recorded in this sequence. The chronology obtained from varve counting constitutes a floating chronology of an interglacial period; the recovery of two tephra layers allowed to fix the floating chronology to the interglacial centred at 400 ka BP, thus corresponding to MIS 11. I studied the upper 5,900 varves at seasonal resolution, using a multi proxy approach. The thickness of summer layers is the proxy for productivity and spring-summer temperature, whereas detrital layers indicate extreme precipitation events; δ18O has been used as a proxy for temperature and/or air masses circulation. I developed a new sampling technique for isotope analyses, in order to ensure the sampling of endogenic calcite, avoiding detrital contamination; this method also allowed me to quantify the effect of Triassic dolomite in bulk carbonate samples. The 15.5 ka of interglacial conditions in Piànico are characterised by short-term climate change. At least four rapid climatic oscillations and a climatic deterioration at the very end of the 15,500 years are recorded. The main climatic oscillation is a 1000 years long cold period that took place after ca 10,000 years of interglacial conditions. This type of climate oscillation has not been recorded in the Holocene yet. This implies that, so far, the Holocene has not experienced all the possible range of interglacial climate changes.

Beschreibung: We present seismic images of the upper mantle beneath Eastern Turkey determined by teleseismic tomography. The data are measured precisely from seismograms recoded by the Eastern Turkey Seismic Experiment network consisting of 29 portable stations and 2 permanent stations. Our results show that obvious high-velocity (high-V) anomalies of up to 2% are interrupted beneath Eastern Turkey, and subcrustal earthquakes occurred along these high-V anomalies. Pronounced low-velocity (low-V) anomalies are visible from the Arabian foreland basin in the southwest to the Caucasus region in the northeast, which extend down to about 400 km depth. These low-V anomalies are consistent with the existence of Late Cenozoic volcanism in the region. These results provide new constraints on the geodynamic processes in the east Anatolian plateau, suggesting that the break-off of the Arabian slab may play an important role in the formation of the Anatolian plateau and the volcanism in the region. These processes might be related to the collision of the Arabian plate with the Eurasian plate.

Beschreibung: The goal of this study is to refine knowledge of the structure and tectonic history of the European Arctic using the combination of all available seismological surface wave data, including historical data that were not used before for this purpose. We demonstrate how the improved data coverage leads to better depth and spatial resolution of the seismological model and discovery of intriguing features of upper-mantle structure. To improve the surface wave data set in the European Arctic, we extensively searched for broad-band data from stations in the area from the beginning of the 1970s until 2005. We were able to retrieve surface wave observations from regional data archives in Norway, Finland, Denmark and Russia in addition to data from the data centres of IRIS and GEOFON. Rayleigh and Love wave group velocity measurements between 10 and 150 s period were combined with existing data provided by the University of Colorado at Boulder. This new data set was inverted for maps showing the 2-D group-velocity distribution of Love and Rayleigh waves for specific periods. Using Monte Carlo inversion, we constructed a new 3-D shear velocity model of the crust and upper mantle beneath the European Arctic which provides higher resolution and accuracy than previous models. A new crustal model of the Barents Sea and surrounding areas, published recently by a collaboration between the University of Oslo, NORSAR and the USGS, constrains the 3-D inversion of the surface wave data in the shallow lithosphere. The new 3-D model, BARMOD, reveals substantial variations in shear wave speeds in the upper mantle across the region with a nominal resolution of 1° × 1°. Of particular note are clarified images of the mantle expression of the continent-ocean transition in the Norwegian Sea and a deep, high wave speed lithospheric root beneath the Eastern Barents Sea, which presumably is the remnant of several Palaeozoic collisions.

Beschreibung: Structural features associated with fore-arc basins appear to strongly influence the rupture processes of large subduction zone earthquakes. Recent studies demonstrated that a significant percentage of the global seismic moment release on subduction zone thrust faults is concentrated beneath the gravity lows resulting from fore-arc basins. To better determine the nature of this correlation and to examine its effect on rupture directivity and termination, we estimated the rupture areas of a set of Mw 7.5–8.7 earthquakes that occurred in circum-Pacific subduction zones. We compare synthetic and observed seismograms by measuring frequency-dependent amplitude and arrival time differences of the first orbit Rayleigh waves. At low frequencies, the amplitude anomalies primarily result from the spatial and temporal extent of the rupture. We then invert the amplitude and arrival time measurements to estimate the second moments of the slip distribution which describe the rupture length, width, duration, and propagation velocity of each earthquake. Comparing the rupture areas to the trench-parallel gravity anomaly (TPGA) above each rupture, we find that in 11 of the 15 events considered in this study the TPGA increases between the centroid and the limits of the rupture. Thus local increases in TPGA appear to be related to the physical conditions along the plate interface that favor rupture termination. Owing to the inherently long timescales required for fore-arc basin formation, the correlation between the TPGA field and rupture termination regions indicates that long-lived material heterogeneity rather than short timescale stress heterogeneities are responsible for arresting most great subduction zone ruptures.

Beschreibung: [1] We provide a procedure for the routine determination of moment tensors from earthquakes with magnitudes as low as MW 4.4 using data recorded by only a few permanent seismic stations at regional to teleseismic distances. Waveforms are inverted for automatically determined frequency pass-bands that depend on source-receiver locations as well as the earthquake magnitude. Inversion results are stable against small variations in the frequency band and provide low data variances, i.e., a good fit between observed and modelled waveform traces. The total frequency band used for our procedure ranges from 10 mHz to 29 mHz (periods of 35 s to 100 s). This enables us to determine focal mechanisms for earthquakes that were not derived previously by routine procedures of CMT or other agencies. As a case study, we determine focal mechanism solutions of 38 light to moderate magnitude earthquakes in eastern Africa between 1995 and 2002.

Beschreibung: Seismic broad-band sensors are known to be sensitive to the magnetic field. Magnetic storms and man-made disturbances of the magnetic field can produce significant noise in seismic recordings. I show that variations in the magnetic field translate directly into apparent acceleration of the seismic sensor within the period range from 60 to 1200 s for all leaf-spring sensors under investigation. For a Streckeisen STS-1V this is shown even for periods down to 1 s. The sensitivity is quantified in magnitude and direction. Both are quite stable over many time windows and signal periods. The sensitivities obtained by linear regression of the acceleration signal on magnetic field recordings during a magnetic storm can effectively be applied to reduce noise in seismic signals. The sensitivity varies in magnitude from sensor to sensor but all are in the range from 0.05 to 1.2 m s−2 T−1. Seismograms from sensors at Black Forest Observatory (BFO) and stations of the German Regional Seismic Network were investigated. Although these are mainly equipped with leaf-spring sensors, the problem is not limited to this type of instrument. The effect is not observable on the horizontal component STS-1s at BFO while it is significant in the recordings of the vertical STS-1. The main difference between these instruments is the leaf-spring suspension in the vertical component that appears to be the source of the trouble. The suspension springs are made of temperature compensated Elinvar alloys that inherently are ferromagnetic and may respond to the magnetic field in various ways. However, the LaCoste Romberg ET-19 gravimeter at BFO, which uses this material too, does not respond to magnetic storms at a similar magnitude neither do the Invar-wire strainmeters. An active shielding, composed of three Helmholtz coils and a feedback system, is installed at station Stuttgart and provides an improvement of signal-to-noise ratio by almost a factor of 20 at this particular station. The passive Permalloy shielding commonly installed with STS-1V sensors performs similarly well.

Beschreibung: The formation of pyrite (FeS2) from iron monosulfide precursors in anoxic sediments has been suggested to proceed via mackinawite (FeS) and greigite (Fe3S4). Despite decades of research, the mechanisms of pyrite formation are not sufficiently understood because solid and dissolved intermediates are oxygen-sensitive and poorly crystalline and therefore notoriously difficult to characterize and quantify. In this study, hydrothermal synchrotron-based energy dispersive X-ray diffraction (ED-XRD) methods were used to investigate in situ and in real-time the transformation of mackinawite to greigite and pyrite via the polysulfide pathway. The rate of formation and disappearance of specific Bragg peaks during the reaction and the changes in morphology of the solid phases as observed with high resolution microscopy were used to derive kinetic parameters and to determine the mechanisms of the reaction from mackinawite to greigite and pyrite. The results clearly show that greigite is formed as an intermediate on the pathway from mackinawite to pyrite. The kinetics of the transformation of mackinawite to greigite and pyrite follow a zero-order rate law indicating a solid-state mechanism. The morphology of greigite and pyrite crystals formed under hydrothermal conditions supports this conclusion and furthermore implies growth of greigite and pyrite by oriented aggregation of nanoparticulate mackinawite and greigite, respectively. The activation enthalpies and entropies of the transformation of mackinawite to greigite, and of greigite to pyrite were determined from the temperature dependence of the rate constants according to the Eyring equation. Although the activation enthalpies are uncharacteristic of a solid-state mechanism, the activation entropies indicate a large increase of order in the transition state, commensurate with a solid-state mechanism.

Beschreibung: Here we present the results of local source tomographic inversion beneath central Java. The data set was collected by a temporary seismic network. More than 100 stations were operated for almost half a year. About 13,000 P and S arrival times from 292 events were used to obtain three-dimensional (3-D) Vp, Vs, and Vp/Vs models of the crust and the mantle wedge beneath central Java. Source location and determination of the 3-D velocity models were performed simultaneously based on a new iterative tomographic algorithm, LOTOS-06. Final event locations clearly image the shape of the subduction zone beneath central Java. The dipping angle of the slab increases gradually from almost horizontal to about 70°. A double seismic zone is observed in the slab between 80 and 150 km depth. The most striking feature of the resulting P and S models is a pronounced low-velocity anomaly in the crust, just north of the volcanic arc (Merapi-Lawu anomaly (MLA)). An algorithm for estimation of the amplitude value, which is presented in the paper, shows that the difference between the fore arc and MLA velocities at a depth of 10 km reaches 30% and 36% in P and S models, respectively. The value of the Vp/Vs ratio inside the MLA is more than 1.9. This shows a probable high content of fluids and partial melts within the crust. In the upper mantle we observe an inclined low-velocity anomaly which links the cluster of seismicity at 100 km depth with MLA. This anomaly might reflect ascending paths of fluids released from the slab. The reliability of all these patterns was tested thoroughly.

Beschreibung: We present an update, for years 2003 and 2004, of the European– Mediterranean Regional Centroid Moment Tensor (RCMT) catalog that we maintain since 1997. This update adds 177 new solutions to the database, relating to moderate-magnitude () earthquakes. About 30% of our new solutions also appear in the global CMT catalog: comparison of the two independent determinations generally shows very good agreement. Within the time span covered, the most noticeable seismic sequences occurred in Northern Africa (Boumerdes, Algerian coast in 2003 and Al Hoceima, Morocco in 2004) and in Southern Greece and Dodecanese region (August 2003 and 2004). The complete RCMT catalog for the European and Mediterranean region now covers 8 years, and contains about 600 solutions.

Beschreibung: Background: A profile across 8 layers from a fossil travertine terrace from a low temperature geothermal spring located in Svalbard, Norway has been studied using both Raman spectroscopy and SEM (Scanning Electron Microscopy) techniques to identify minerals and organic life signals. Results: Calcite, anatase, quartz, haematite, magnetite and graphite as well as scytonemin, three different carotenoids, chlorophyll and a chlorophyll-like compound were identified as geo- and biosignatures respectively, using 785 and/or 514 nm Raman laser excitation wavelengths. No morphological biosignatures representing remnant microbial signals were detected by high-resolution imaging, although spectral analyses indicated the presence of organics. In contrast, in all layers, Raman spectra identified a series of different organic pigments indicating little to no degradation or change of the organic signatures and thus indicating the preservation of fossil biomarker compounds throughout the life time of the springs despite the lack of remnant morphological indicators. Conclusion: With a view towards planetary exploration we discuss the implications of the differences in Raman band intensities observed when spectra were collected with the different laser excitations. We show that these differences, as well as the different detection capability of the 785 and 514 nm laser, could lead to ambiguous compound identification. We show that the identification of bio and geosignatures, as well as fossil organic pigments, using Raman spectroscopy is possible. These results are relevant since both lasers have been considered for miniaturized Raman spectrometers for planetary exploration.

Beschreibung: It has recently been shown that correlations of seismic noise can contain significant information about the Green's function along the station profile. Using an array of 38 temporary broad-band stations located in Finland between 1998 September and 1999 March, we study the resulting 703 noise correlations to understand how they are influenced by the directivity of the noise field. The latter information is obtained through f-k analysis of data from two permanent seismic arrays in Germany and Norway and from a subset of stations of the array in Finland. Both types of analysis confirm that the characteristic of the seismic noise is strongly frequency-dependent. At low frequencies (0.02-0.04 Hz), we observe diffuse noise and/or randomly distributed sources. In contrast, the noise is strongly direction-dependent and not fully diffuse in the intermediate period ranges (0.04-0.25 Hz) which correspond to the first and second micro seismic peak, created at the Irish and Scottish coast and the western coast of Norway In this frequency interval the noise is sufficiently close to a plane wave to introduce systematic errors in group velocities for station pairs which are not parallel to the direction of the dominant incident noise. Phase velocities calculated by slant stack over many traces are however correct, independently of profile direction. In the high-frequency band (0.25-1.0 Hz), the situation is a mix between the low-frequency and the intermediate frequency cases. Average phase velocities and individual group velocities from well-oriented profiles are in excellent agreement with results from Rayleigh wave studies of the area.