Detailed analysis of the geomagnetic ground survey performed in middle-northern Croatia over the time interval 2003–2005

During the time interval 2003–2005 a ground survey of the total magnetic field intensity in the middle-northern part of Croatia was performed, in order to get a detailed insight of the field distribution over the region. A special effort was done to understand the uncertainty and errors in data reduction, namely different amplitudes of the diurnal variations and different secular variations at the ground stations with respect to the observatories. For data reduction to epoch 2004.5 the total field recordings from AQU, FUR, NCK and THY geomagnetic observatories have been used. We estimate the mean determination error to be one order of magnitude smaller than the maximal reduction error. Multiple linear regression and the method of empirical orthogonal functions were applied on the ground survey and observatory time series. This allowed us to explain the correlations among them and the variance of the total field. Furthermore, we identified two sources of serious artificial disturbances caused by DC leakage: the tramway system of the capital and one railway station in neighbouring Slovenia. Also, we estimate the region free of these disturbances. The magnitude of one of them is estimated to be more than five nT at the distance of about 10 km.     

Probabilistic failure analysis of riprap as riverbank protection under flood uncertainties

Existing riverbank riprap could face the risk of failure if the flood regime changes in future. Additionally, changed sediment transport in rivers, as a possible result of climate change, impacts the failure risk of flood protection measures. Evaluation of this potential failure is the primary issue of riprap stability and safety assessment. The consequences of the bank failure are probably uncontrolled erosion and flooding with disastrous consequences in residential areas or damage to infrastructures. Thus, a probabilistic analysis of riprap failure considering different mechanisms due to the flood and sediment transport uncertainties is required to assess embankment stability. In this article, the concept of a probabilistic assessment model based on Monte Carlo simulation method, moment analysis methods, and Rosenblueth point estimation method are presented to define the failure risk of riprap as the river bank protection. The probability of failure in different modes, namely direct block erosion, toe scouring and overtopping, has been defined by taking into account the river bed level variation based on bedload transport described with a probabilistic function of the peak discharge. The result of three models comparison revealed a good agreement (the average deviation of less than 2%) in estimation of riprap failure probability. This model is a strategical tool to search the critical river reaches and helps to evaluate the risk maps. So that, the model could cover the engineering aspect of environmental stability in the rivers with riprap as the bank protections.     

Criteria for recognizing shelf-slope clinoforms in outcrop; Jurassic Lajas and Los Molles formations,S. Neuquén Basin,Argentina

Seismic-reflection data show that most deepwater (>200 m water depth) basins are filled by sand and mud dispersed across clinoformal geometries characterized by gently dipping topsets, steeper foresets and gently dipping bottomsets. However, the entire geometry of these ubiquitous clinoforms is not always recognized in outcrops. Sometimes the infill is erroneously interpreted as “layer cake” or “ramp” stratigraphy because the topset-foreset-bottomset clinoforms are not well exposed. Regional 2-D seismic lines show clinoforms in the Lower to Middle Jurassic Challaco, Lajas, and Los Molles formations in S. Neuquén Basin in Argentina. Time equivalent shelf, slope and basin-floor segments of clinoforms are exposed, and can be walked out in hundreds of metres thick and kilometres-wide outcrops. The studied margin-scale clinoforms are not representing a continental-margin but a deepwater shelf margin that built out in a back-arc basin. Lajas-Los Molles clinoforms have been outcrop-mapped by tracing mudstones interpreted as flooding surfaces on the shelf and abandonment surfaces (low sedimentation rate) in the deepwater basin. The downslope and lateral facies variability in the outcrops is also consistent with a clinoform interpretation. The Lajas topset (shelf) is dominated by fluvial and tidal deposits. The shelf-edge rollover zone is occasionally occupied by a 40–50-m-thick coarse-grained shelf-edge delta, sometimes incising into the underlying slope mudstones, producing oblique clinoforms expressing toplap erosion on seismic. A muddy transgressive phase capping the shelf-edge deltas contains tidal sandbodies. Shelf-edge deltas transition downslope into turbidite- and debris flow-filled channels that penetrate down the mud-prone Los Molles slope. At the base-of-slope, some 300m below the shelf edge, there are basin-floor fan deposits (>200 m thick) composed of sandy submarine-fan lobes separated by muddy abandonment intervals. The large-scale outcrop correlation between topset–foreset–bottomset allows facies and depositional interpretation and sets outcrop criteria recognition for each clinoform segment.     

Analytical development of the lunisolar disturbing function and the critical inclination secular resonance

We provide a detailed derivation of the analytical expansion of the lunar and solar disturbing functions. Although there exist several papers on this topic, many derivations contain mistakes in the final expansion or rather (just) in the proof, thereby necessitating a recasting and correction of the original derivation. In this work, we provide a self-consistent and definite form of the lunisolar expansion. We start with Kaula’s expansion of the disturbing function in terms of the equatorial elements of both the perturbed and perturbing bodies. Then we give a detailed proof of Lane’s expansion, in which the elements of the Moon are referred to the ecliptic plane. Using this approach the inclination of the Moon becomes nearly constant, while the argument of perihelion, the longitude of the ascending node, and the mean anomaly vary linearly with time. We make a comparison between the different expansions and we profit from such discussion to point out some mistakes in the existing literature, which might compromise the correctness of the results. As an application, we analyze the long-term motion of the highly elliptical and critically-inclined Molniya orbits subject to quadrupolar gravitational interactions. The analytical expansions presented herein are very powerful with respect to dynamical studies based on Cartesian equations, because they quickly allow for a more holistic and intuitively understandable picture of the dynamics.     

Mathematical models of climate evolution in Dobrudja

The understanding of processes that occur in climate change evolution and their spatial and temporal variations are of major importance in environmental sciences. Modeling these processes is the first step in the prediction of weather change. In this context, this paper presents the results of statistical investigations of monthly and annual meteorological data collected between 1961 and 2007 in Dobrudja (a region situated in the South–East of Romania between the Black Sea and the lower Danube River) and the models obtained using time series analysis and gene expression programming. Using two fundamentally different approaches, we provide a comprehensive analysis of temperature variability in Dobrudja, which may be significant in understanding the processes that govern climate changes in the region.     

Reconstructing the spatial distribution of large vegetation formations during the mid-Holocene in Romania: a predictive modeling approach

The present study tests the usefulness of SoLIM software and GIS techniques for the reconstruction of large vegetation formations from the mid-Holocene period in Romania. We used current reference climate data (temperature, precipitation) and the current extent of ecological regions in Romania to derive climate optimality functions for each vegetation formation. The optimality functions were used to simulate current and past distributions of vegetation. The results showed that the current and mid-Holocene simulated spatial distributions of vegetation are quite similar. Changes were found for about 14% of the Romanian territory (33 946 km²), the most important being the retreat of coniferous forests in favor of mixed forests and of mixed forests in favor of forest steppe. The former is validated by previous pollen-based studies showing the transition from coniferous forests to mixed forests that occurred in several areas of the country after the mid-Holocene. The study demonstrates the potential of this methodological approach to reconstruct past vegetation formations, and at the same time that it is a straightforward and expert knowledge-based method. Although our application uses only climate factors, the results can be further refined by incorporating additional drivers (soil and landform information, site-specific pollen and fossil data, wildfire data) for a more accurate inference of paleovegetation.     

Advanced real-time acquisition of the Vrancea earthquake early warning system

The Vrancea seismogenic zone in Romania represents a peculiar source of seismic hazard, which is a major concern in Europe, especially to neighboring regions of Bulgaria, Serbia and Republic of Moldavia. Earthquakes in the Carpathian–Pannonian region are confined to the crust, except the Vrancea zone, where earthquakes with focal depth down to 200 km occur. One of the cities most affected by earthquakes in Europe is Bucharest. Situated at 140–170 km distance from Vrancea epicenter zone, Bucharest encountered many damages due to high energy Vrancea intermediate-depth earthquakes; the March 4, 1977 event (M_w=7.2) produced the collapse of 36 buildings with 8–12 levels, while more than 150 old buildings were seriously damaged. A dedicated set of applications and a method to rapidly estimate magnitude in 4–5 s from detection of P wave in the epicenter were developed. They were tested on all recorded data. The magnitude error for 77.9% of total considered events is in the interval [−0.3, +0.3] magnitude units. This is acceptable taking into account that the magnitude is computed from only 3 stations in a 5 s time interval (1 s delay is caused by data packing). The ability to rapidly estimate the earthquake magnitude combined with powerful real-time software, as parts of an early warning system, allows us to send earthquake warning to Bucharest in real time, in about 5 s after detection in the epicenter. This allows 20–27 s warning time to automatically issue preventive actions at the warned facility.     

Wave propagation in protoplanetary disks: Formation of twin planets by ‘disk-brown dwarf’ collisions?

In this paper we derive a special linear non-vortical wave propagation solution in the shearing sheet, a model of a compressible two-dimensional fluid system with constant density, constant shear and constant Coriolis force, but without self-gravity. The linear analysis of the shearing sheet leads to a single differential equation for the azimuthal velocity perturbation. A detailed derivation of a special solution with a prescribed azimuthal wavenumber k is presented. More general wave solutions, eventually excited by large local ‘impacts’, can be derived by superimposing all k-modes. The special wave functions so obtained describe the formation of two independent spiral wave arms originating out of a ring-shaped structure. The motivation for this investigation lies in the fact that similar wave propagators can be excited by the transit of a solid or ‘clumpy’ object through a protoplanetary disk. We speculate that a disk-brown dwarf collision can produce in the disk a pair of two spiral density wave fragments triggering the rapid accretion of two giant planets by a gravitational shear instability simultaneously (Hypothesis of a mechanism for the production of giant planets in pairs).     

Growth of chloritoid and garnet along a nearly isothermal burial path to 70 km depth: an example from the Bughea Metamorphic Complex,Leaota Massif,South Carpathians

Mineralogy and Petrology - Chloritoid-bearing micaschist occurs in the matrix of a subduction mélange (Bughea Complex) of the Leaota Massif (South Carpathians) containing blocks of...