Seismic Ground Motion Expected for the Eastern District of Naples

The seismic ground motion of a test area in the eastern district of Naples is computed with a hybrid technique based on the mode summation and the finite difference methods. This technique allows us the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, we consider the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, which is located about 90 km from the epicenter.The detailed geological setting is reconstructed from a large number of drillings. The sub-soil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow neapolitan tuff), representing the neapolitan bedrock. The detailed information available on mechanical properties of the sub-soil and its geometry warrants the application of the sophisticated hybrid technique.As expected, the sedimentary cover causes an increase of the signal's amplitudes and duration. If thin peat layers are present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such layers, that tend to seismically decouple the upper from the lower part of the structure.For SH-waves, the influence of the variations of the S-wave velocities on the spectral amplification is studied, by considering locally measured velocities and values determined from near-by down-hole measurements. The comparison between the computed spectral amplifications confirms the key role of an accurate determination of the seismic velocities of the different layers.The comparison performed between a realistic 2-D seismic response and a standard 1-D response, based on the vertical propagation of waves in a plane layered structure, shows considerable difference, from which it is evident that serious caution must be taken in the modelling of expected ground motion at a specific site.     

Platinum-group elements in alpine-type ultramafic rocks and related chromite ores of the main ophiolite belt of the Urals

On the basis of a representative collection of ultramafic rocks and chromite ores and a series of technological samples from the largest (Central and Western) deposits in the Rai-Iz massif of the Polar Urals and the Almaz-Zhemchuzhina and Poiskovy deposits in the Kempirsai massif of the southern Urals, the distribution and speciation of platinum-group elements (PGE) in various type sections of mafic-ultramafic massifs of the Main ophiolite belt of the Urals have been studied. Spectral-chemical and spectrophotometric analyses were carried out to estimate PGE in 700 samples of ultramafic rocks and chromite ores; 400 analyses of minerals from rocks, ores, and concentrates and 100 analyses of PGE minerals (PGM) in chromite ores and concentrates were performed using an electron microprobe. Near-chondritic and nonchondritic PGE patterns in chromitebearing sections have been identified. PGE mineralization has been established to occur in chromite ore from all parts of the mafic-ultramafic massifs in the Main ophiolite belt of the Urals. The PGE deposits and occurrences discovered therein are attributed to four types (Kraka, Kempirsai, Nurali-Upper Neiva, and Shandasha), which are different in mode of geological occurrence, geochemical specialization, and placer-forming capability. Fluid-bearing minerals of the pargasite-edenite series have been identified for the first time in the matrix of chromite ore of the Kempirsai massif (the Almaz-Zhemchuzhina deposit) and Voikar-Syn’ya massif (the Kershor deposit). The PGE grade in various types of chromite ore ranges from 0.1–0.2 to 1–2 g/t or higher. According to technological sampling, the average PGE grade in the largest deposits of the southeastern ore field of the Kempirsai massif is 0.5–0.7 g/t. Due to the occurrence of most PGE as PGM 10–100 mm in size and the proved feasibility of their recovery into nickel alloys, chromites of the Kempirsai massif can be considered a complex ore with elevated and locally high Os, Ir, and Ru contents. The Nurali-Upper Neiva type of ore is characterized by small-sized primary deposits, which nevertheless are the main source of large Os-Ir placers in the Miass and Nev’yansk districts of the southern and central Urals, respectively.     

Residual deformations and seismic hazard of fault zones in underground workings

The results of long-term measurements of residual deformations in the area of the Severomuiskii tunnel during its construction are given. Comparison of spatial and temporal distributions between deformations and earthquakes shows that they are interrelated. The nonlinear behavior of disintegrated and waterlogged rocks within tectonic fault zones should be taken into account even for moderate intensity earthquakes, since they are accompanied by ground subsidence. Underground workings within such sites are subjected to loads that are greater than expected according to current hypotheses, which are the basis for calculations of rock pressure. It is established that the most probable mechanism of ground subsidence and residual deformation in underground workings could be the gravity load of the overlying strata of disintegrated and waterlogged rocks within a fault zone, which leads to instability of the rocks. Approximate stress estimations are made on the basis of the results of measurements of residual deformations of roof supports (linings).     

Impact of Sea-level Rise and Storm Surges on a Coastal Community

A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions.     

Peculiarities of Dynamic Slip Nucleation in a Thin Granular Layer

Izvestiya, Physics of the Solid Earth - Abstract—Granular media determine the dynamics of many natural systems including faults in the Earth’s crust. The paper addresses the laboratory...     

PROBLEMS IN CONSTRUCTING A BATHYMETRIC BASE MAP FOR THE GULF OF FINLAND

The various steps required for compilation of a bathymetric chart of the Gulf of Finland are outlined, taking into account the specific conditions characteristic of that water body. The use of available initial source materials and special survey work required for supplementing these sources is discussed. Translated by Edward Torrey, Alexandria, VA 22308 from: Geodeziya i kartografiya, 1988, No. 8, pp. 40-42.     

Marine risk assessment: linear alkylbenzenesulponates (LAS) in the North Sea

The fate of linear alkylbenzenesulponates (LAS) in estuaries and coastal areas of the North Sea has been characterized with simple environmental models. The predicted concentration range in the estuaries around the North Sea (0.9-9 microg LAS l(-1)) was validated by monitoring data (1-9 microg LAS l(-1)). In offshore sites of the North Sea, it is estimated--and experimentally verified for a few sites--that the LAS concentration is below analytical detection limit (i.e., 0.5 microg LAS l(-1)). The effects of LAS on marine organisms have been reviewed. For short-term acute tests, there was no significant difference (p = 0.83) between the mean LC50 values of freshwater and marine organisms (mainly pelagic species tested, 4.1 and 4.3 mg LAS l(-1), respectively). For longer-term chronic tests, it appeared that the sensitivity (mean no-observed effect concentration (NOEC) value) of marine and freshwater organisms (0.3 and 2.3 mg LAS l(-1), respectively) was significantly different pt-test = 0.007). The predicted no-effect-concentrations (PNEC) were 360 and 31 microg LAS l(-1), for freshwater and marine pelagic communities, respectively. Given that the maximum expected estuarine and marine concentrations are 3 to > 30 times lower than the PNEC, the risk of LAS to pelagic organisms in these environments is judged to be low.