Assessment of river habitat in Brandenburg, Germany

A habitat assessment of 1,707 km of rivers in the Federal State of Brandenburg, Germany, was undertaken using the desk-based ‘overview method’. This method includes the analysis of different sources such as topographic and thematic maps, reports, remote sensing data, and interviews with authorities. It compares actual habitat conditions with natural conditions, and assesses the human disturbances using a seven-step scale. Results show, that in Brandenburg more than 50% of surveyed river units are heavily (class 5) to totally disturbed (class 7) and only slightly more than 20% are undisturbed (class 1) to little disturbed (class 2). Main human disturbances are canalization, bank stabilizations, flood control, migration barriers, and agricultural and urban development in the floodplain. All survey data and maps are embedded in a geographical information system (GIS) that not only allows future analysis and use in river restoration management by experts, but also serves as information for the public. The river habitat map of Brandenburg is part of the river habitat map of the entire Germany.     

Dynamical System Analysis and Forecasting of Deformation Produced by an Earthquake Fault

— We present a method of constructing low-dimensional nonlinear models describing the main dynamical features of a discrete 2-D cellular fault zone, with many degrees of freedom, embedded in a 3-D elastic solid. A given fault system is characterized by a set of parameters that describe the dynamics, rheology, property disorder, and fault geometry. Depending on the location in the system parameter space, we show that the coarse dynamics of the fault can be confined to an attractor whose dimension is significantly smaller than the space in which the dynamics takes place. Our strategy of system reduction is to search for a few coherent structures that dominate the dynamics and to capture the interaction between these coherent structures. The identification of the basic interacting structures is obtained by applying the Proper Orthogonal Decomposition (POD) to the surface deformation fields that accompany strike-slip faulting accumulated over equal time intervals. We use a feed-forward artificial neural network (ANN) architecture for the identification of the system dynamics projected onto the subspace (model space) spanned by the most energetic coherent structures. The ANN is trained using a standard back-propagation algorithm to predict (map) the values of the observed model state at a future time, given the observed model state at the present time. This ANN provides an approximate, large-scale, dynamical model for the fault. The map can be evaluated once to provide a short-term predictions or iterated to obtain a prediction for the long-term fault dynamics.     

Scale and timing of Rare Earth Element redistribution in the Taconian foreland of New England

Clastic sedimentary rocks, deposited on eastern North America in response to the Taconian Orogeny, commonly have Sm/Nd isotope relationships indicating substantial isotope disturbance near or subsequent to the time of sedimentation that may be associated with severe depletion in light rare earth elements (LREE). Affected units [Normanskill Formation (Austin Glen and Pawlet Members), Frankfort Formation and Perry Mountain Formation] are widely separated both geographically (western New York to western Maine) and stratigraphically (Middle Ordovician to Silurian). A model is proposed for the most likely explanation of the observed REE and Sm/Nd isotope relationships involving a two‐stage process. In the first stage, REE are redistributed on a mineralogical scale (dissolution/precipitation on a sample scale) often with the involvement of REE‐enriched trace phases such as apatite and monazite. This stage typically takes place during diagenesis but may also take place later during metamorphism and/or recent weathering, and results in isotope re‐equilibration on a sample scale. The second stage occurs when one or more of these phases is redissolved and REE are transported on large advective scales. Where LREE‐enriched phases are involved, this gives rise to LREE depletion in whole rocks. The timing of this second stage cannot be constrained from Sm/Nd isotope data and may take place at any time subsequent to the isotope re‐equilibration. Such complex histories of REE redistribution may result in serious errors in estimating Nd model ages but not in estimating the Nd isotope composition at the age of sedimentation. Thus, Sm/Nd ratios even of unmetamorphosed sedimentary rocks have to be carefully evaluated before the calculation of depleted mantle model ages for the provenance.     

Estimating crustal deformations from a combination of baseline measurements and geophysical models

The estimation of crustal deformations from repeated baseline measurements is a singular problem in the absence of prior information. One often applied solution is a free adjustment in which the singular normal matrix is augmented with a set of inner constraints. These constraints impose no net translation nor rotation for the estimated deformations X which may not be physically meaningful for a particular problem. The introduction of an available geophysical model from which an expected deformation vector \(\bar X\) and its covariance matrix \(\sum _{\bar X} \) can be computed will direct X to a physically more meaningful solution. Three possible estimators are investigated for estimating deformations from a combination of baseline measurements and geophysical models.     

Geological Observations of Damage Asymmetry in the Structure of the San Jacinto, San Andreas and Punchbowl Faults in Southern California: A Possible Indicator for Preferred Rupture Propagation Direction

We present new in situ observations of systematic asymmetry in the pattern of damage expressed by fault zone rocks along sections of the San Andreas, San Jacinto, and Punchbowl faults in southern California. The observed structural asymmetry has consistent manifestations at a fault core scale of millimeters to meters, a fault zone scale of meters to tens of meters and related geomorphologic features. The observed asymmetric signals are in agreement with other geological and geophysical observations of structural asymmetry in a damage zone scale of tens to hundreds of meters. In all of those scales, more damage is found on the side of the fault with faster seismic velocities at seismogenic depths. The observed correlation between the damage asymmetry and local seismic velocity structure is compatible with theoretical predictions associated with preferred propagation direction of earthquake ruptures along faults that separate different crustal blocks. The data are consistent with a preferred northwestward propagation direction for ruptures on all three faults. If our results are supported by additional observations, asymmetry of structural properties determined in field studies can be utilized to infer preferred propagation direction of large earthquake ruptures along a given fault section. The property of a preferred rupture direction can explain anomalous behavior of historic rupture events, and may have profound implications for many aspects of earthquake physics on large faults.     

Temporal Changes of Shallow Seismic Velocity Around the Karadere-Düzce Branch of the North Anatolian Fault and Strong Ground Motion

We analyze temporal variations of seismic velocity along the Karadere-Düzce branch of the north Anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 M_w7.4 İzmit and M_w7.1 Düzce earthquakes. The analysis employs 36 sets of highly repeating earthquakes, each containing 4–18 events. The events in each cluster are relocated by detailed multi-step analysis and are likely to rupture approximately the same fault patch at different times. The decay rates of the repeating events in individual clusters are compatible with the Omori's law for the decay rate of regional aftershocks. A sliding window waveform cross-correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events. We find clear step-like delays in the direct S and early S-coda waves (sharp seismic velocity reduction) immediately after the Düzce main shock, followed by gradual logarithmic-type recoveries. A gradual increase of seismic velocities is also observed before the Düzce main shock, probably reflecting post-seismic recovery from the earlier İzmit main shock. The temporal behavior is similar at each station for clusters at various source locations, indicating that the temporal changes of material properties occur in the top most portion of the crust. The effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones, and generally decrease with normal distance from the fault. A strong correlation between the co-seismic delays and intensities of the strong ground motion generated by the Düzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material.     

Sources of mud volcano fluids in the Gulf of Cadiz—indications for hydrothermal imprint

Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the European-African plate boundary, affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness. The investigation of six active sites shows that mud volcano (MV) fluids, on average, are highly enriched in CH₄, Li, B, and Sr and depleted in Mg, K, and Br. The purity of the fluids is largely controlled by the intensity of upward directed flow. Flow rates could be constrained by numerical modelling and vary between <0.05 and 15 cm yr⁻¹. Application of δD-δ¹⁸O systematics identifies clay mineral dehydration, most likely within Mesozoic and Tertiary shales and marls, as the major source of fluids. Hence, Cl and Na in the pore fluids are mostly depleted below seawater values, following a general trend of dilution. However, deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits. Other secondary processes overprinting the original fluid composition may occur along the flow path, such as dissolution of anhydrite or gypsum and/or the formation of calcite and dolomite. Different sources of fluids are also indicated by variations in ⁸⁷Sr/⁸⁶Sr, which range from 0.7086 to 0.7099 at the different sites. Dehydration may be induced primarily by overburden and tectonic compression; however, very high concentrations of Li and B, specifically at Captain Arutyunov MV (CAMV) indicate additional leaching at temperatures above 150 °C, which could be explained by the injection of hot fluids along deep penetrating, major E-W strike-slip fault systems. This hypothesis is supported by the occurrence of generally thermogenic, but significantly CH₄-enriched, light volatile hydrocarbon gases at CAMV which cannot be explained by shallow microbial methanogenesis. Li and Li/B ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies.