Natural and anthropogenic sources of total suspended particulate and their contribution to the formation of black crusts on building stone materials of Catania (Sicily)

Blackening and disaggregation of exposed surfaces of stone monuments are well-known effects of stone decay taking place in polluted urban environments all over the world. This paper aims to assess the contribution of natural and anthropogenic sources of total suspended particulate (TSP) causing permanent damage (black crusts) to the stone monuments of Catania (Sicily), one of the most popular ??cities of art?? of southern Italy. Atmospheric pollution of Catania, a typical Mediterranean coastal town, is mainly contributed by vehicle exhaust emissions rather than industrial ones. Episodically, the city also suffers gaseous and ash emissions (plumes) from the nearby Mount Etna volcano. Thus, to discriminate between natural and anthropogenic contributions to stone decay on Catania monuments, black crusts and TSP were sampled within the urban area and subjected to specific analytical procedures (optical microscopy, X-ray powder diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy equipped with energy dispersive spectrometry, ionic chromatography and dual inlet mass spectrometry). Mineralogical, chemical and isotopic characterization of black crusts and TSP provided new insights concerning the partition of sulfate sources in this particular urban context. The influence of Mount Etna emissions on both TSP and black crusts compositions was shown. Nevertheless, the key role of anthropogenic sources in the total sulfate budget was confirmed, while sea spray and volcanic emissions were found to make subordinate contributions. Quantitative data useful for the identification of the threshold pollution levels for preventive conservation of Catania monuments were obtained.     

Contribution of the SISCam Web-based GIS to the seismotectonic study of Campania (Southern Apennines): an example of application to the Sannio-area

In this article the implementation and potential of the Seismotectonic Information System of the Campania Region (SISCam) are described, in particular an application of this Web-based GIS system to the seismotectonic analysis of the Sannio area (Southern Apennines) is performed. WEB-GIS technologies greatly contribute to both the environmental monitoring and the disaster management of areas affected by high natural risks. Specifically the SISCam system has been developed with the aim of providing easy access and fast diffusion, through Internet technology, of the most significant geological, geophysical, and territorial data relative to the Campania Region. The Sannio area has been selected as our application example because it is among the most active seismic regions in Italy. This portion of the Southern Apennines which was hit by the June 5, 1688 strong earthquake (M _W = 6.7, CPTI 1999) and by some low- and moderate-energy seismic sequences (1990–1992, 1997), is characterized by a complex inherited tectonic setting and low-tectonic deformation rates that hide the seismogenic sources position. Since this case study turned out to be complicated, the use of the SIScam WEB-GIS has become indispensable because it allowed us to visualize, integrate and analyze all the data available, in order to obtain an accurate and direct picture of the seismotectonic setting of the area. Moreover, a different approach of data analysis was necessary, due to the lack of up-to-date neotectonic and structural data; therefore, the operation of this GIS system enabled us to process and generate some original informative layers, through image analysis, such as new structural lineaments represented on a map of the potential active faults of the area, which has been the final result of our application, as a contribution to new knowledge about the local seismic risk parameters.     

Numerical modelling for clays with internal discontinuity surfaces

A numerical model capable of performing deformation analysis of a medium containing discontinuity surfaces is presented. The discontinuity can be either a crack, which can be open or closed, or a shear band. The model consists of two separate numerical algorithms, which are coupled together by means of the principle of superposition. In particular, an integral equation scheme based on the theory of dislocations is adopted for modelling the discontinuity, while a finite element discretization is used for the continuous medium. In this paper the discontinuity modelling is illustrated in detail, together with the specific formulation of the principle of superposition adopted, and some simple examples of application are presented. The well-known modelling approach based on Fracture Mechanics theory is also briefly discussed. The two models are compared and some advantages and drawbacks of each are pointed out, comments are made regarding their applicability in the specific case of soil mechanics, and conclusions are drawn as regards the conditions under which one or the other is appropriate. Finally, a full-scale example of deformation analysis using the proposed model is presented. Copyright © 1999 John Wiley & Sons, Ltd.     

Mass transport triggered by heavy rainfall: the role of endorheic basins and epikarst in a regional karst aquifer

This study aims at recognizing the mechanisms of mass transport between the karst surface and the saturated zone in a morphostructural relief of the Mesozoic karst carbonate platform of Murgia (Puglia, Southern Italy). The large dimension of the karst aquifer, the regional scale of the flow system, the boundary condition constituted by the sea, and the lack of freshwater springs constrain to the use of wells as monitoring points and limit the study area to the recharge area comprising 986 endorheic basins. The concentrations of non‐reactive tracers (nitrates) in the waters of autogenic recharge (from endorheic basins) have been modeled through the evaluation of effective infiltration, land use, and nitrogen surplus, with reference to a time window, which includes a low precipitation period followed by significant rainfall events. The comparison between the modeled nitrate concentrations and the nitrate concentrations measured in ground waters, coupled with the analysis of groundwater chemograms and records of hydraulic heads (all referred to the same time window), allows inferring the mechanism of mass transport between the karst surface and the groundwater table. The mass transport conceptual model requires the presence of the epikarst. The infiltration of significant rainfall in the endorheic basins after a low precipitation period displaces waters stored in the epikarst toward the saturated zone. Ground waters in the post‐event period show higher concentrations of nitrates, lower concentrations of total organic carbon, and higher Mg/Ca ratios than both those of the pre‐event period and the autumn‐winter recharge period. The post‐event recharge from epikarst storage determines a transient hazard of groundwater pollution with a time lag from the occurrence of the heavy rainfall.     

The impact of dredge-fill on Posidonia oceanica seagrass meadows: regression and patterns of recovery

Posidonia oceanica meadows can be severely damaged by dredge-fill operations. We report on the construction of gas pipelines that occurred between 1981 and 1993 in SW Sicily, Italy. A large portion of the meadow was mechanically removed, and the excavated trench was filled with a mosaic of substrates, ranging from sand to consolidated rock debris. Meadow loss and recovery were quantified over 7 years after the end of operations. We recorded an overall loss of 81.20 ha of meadow. Substrate strongly affected recovery as the percent cover by P. oceanica consistently increased on calcareous rubble, reaching values of 44.37 ± 3.05% in shallow sites after 7 years, whereas no significant increase occurred on other substrates. As in the Mediterranean Sea exploitation of coastal areas continues to grow with consequent impacts on P. oceanica meadows, this case study illustrates how artificial rubble-like materials could be employed to support the restoration of damaged meadows.     

A simplified vulnerability model for the extensive liquefaction risk assessment of buildings

Bulletin of Earthquake Engineering - The quantitative assessment of natural risks offers a rational strategy to protect communities, undertake cost effective mitigation and plan the organic and...     

The Late Holocene to Pleistocene tephrostratigraphic record of Lake Ohrid (Albania)

We present in this work a tephrostratigraphic record from a sediment piston core (JO 2004) from Lake Ohrid. Five tephra layers were recognised, all from explosive eruptions of southern Italy volcanoes. A multidisciplinary study was carried out, including stratigraphy, AMS ¹⁴C chronology and geochemistry. The five tephra layers were correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra layers already known in the central Mediterranean area. The oldest is from Pantelleria Island (P11, 131 ka BP). Other three tephra layers are from Campanian volcanoes: X6, Campanian Ignimbrite-Y5 and SMP1-Y3 (107, 39 and 31 ka BP respectively). The youngest tephra layer corresponds to the FL eruption from Etna Volcano (3.4 ka BP). In three cases these recognitions confirm previous findings in the Balkans, while two of them were for the first time recognised in the area, with a significant enlargement of the previous assessed dispersal areas.     

Lava flow hazard at Nyiragongo volcano,D.R.C.

The 2002 eruption of Nyiragongo volcano constitutes the most outstanding case ever of lava flow in a big town. It also represents one of the very rare cases of direct casualties from lava flows, which had high velocities of up to tens of kilometer per hour. As in the 1977 eruption, which is the only other eccentric eruption of the volcano in more than 100 years, lava flows were emitted from several vents along a N–S system of fractures extending for more than 10 km, from which they propagated mostly towards Lake Kivu and Goma, a town of about 500,000 inhabitants. We assessed the lava flow hazard on the entire volcano and in the towns of Goma (D.R.C.) and Gisenyi (Rwanda) through numerical simulations of probable lava flow paths. Lava flow paths are computed based on the steepest descent principle, modified by stochastically perturbing the topography to take into account the capability of lava flows to override topographic obstacles, fill topographic depressions, and spread over the topography. Code calibration and the definition of the expected lava flow length and vent opening probability distributions were done based on the 1977 and 2002 eruptions. The final lava flow hazard map shows that the eastern sector of Goma devastated in 2002 represents the area of highest hazard on the flanks of the volcano. The second highest hazard sector in Goma is the area of propagation of the western lava flow in 2002. The town of Gisenyi is subject to moderate to high hazard due to its proximity to the alignment of fractures active in 1977 and 2002. In a companion paper (Chirico et al., Bull Volcanol, in this issue, 2008) we use numerical simulations to investigate the possibility of reducing lava flow hazard through the construction of protective barriers, and formulate a proposal for the future development of the town of Goma.     

Probabilistic seismic response and reliability assessment of isolated bridges

Bridge seismic isolation strategy is based on the reduction of shear forces transmitted from the superstructure to the piers by two means: shifting natural period and earthquake input energy reduction by dissipation concentrated in protection devices. In this paper, a stochastic analysis of a simple isolated bridge model for different bridge and device parameters is conducted to assess the efficiency of this seismic protection strategy. To achieve this aim, a simple nonlinear softening constitutive law is adopted to model a wide range of isolation devices, characterized by only three essential mechanical parameters. As a consequence of the random nature of seismic motion, a probabilistic analysis is carried out and the time modulated Kanai-Tajimi stochastic process is adopted to represent the seismic action. The response covariance in the state space is obtained by solving the Lyapunov equation for a stochastic linearized system. After a sensitivity analysis, the failure probability referred to extreme displacement and the mean value of dissipated energy are assessed by using the introduced stochastic indices of seismic bridge protection efficiency. A parametric analysis for protective devices with different mechanical parameters is developed for a proper selection of parameters of isolation devices under different situations.