Hydrogeochemistry of Roccamonfina volcano (Southern Italy)

This is the first hydro-geochemical investigation carried out on the Roccamonfina Volcanic Complex groundwaters. The chemistry of Roccamonfina waters is defined by water–rock and water–rock–gas interactions. In fact, interactions between rocks of the first eruptive high-K formations and circulating groundwaters are recognized by high K concentrations. On the other hand, inverse concentration of calcium versus alkali metals is related to two different rock interactions occurring in different areas of the volcano: (a) within the caldera where groundwaters flow within latite and pyroclastic formations releasing calcium, and (b) similarly at the base of the volcano where groundwaters flowing from surrounding carbonates got strongly enriched in Ca. These geochemical processes are also associated with K (SE of caldera) and Mg/Ca (in sites located at the NE base of the volcano) decrease. Completely different dynamics occurs at Riardo groundwaters (SE). Here waters are the result of a mix between the Roccamonfina deep aquifer and the carbonate aquifer of the Riardo plain. Rich-CO₂ emissions make these waters strongly mineralized. Minor elements show a similar geochemical behavior of major ions and are crucial defining interactions processes. The evolution of Roccamonfina groundwaters is also evident along the simultaneous enrichment of Ba, Sr, and Ca. Ba increase is the result of deep local carbonate alteration enhanced by CO₂ emissions and, the lower Sr/Ca ratio, from 10 to 2 (ppb/ppm), is also due to the same process. In the light of our results the Roccamonfina aquifer can be schematically divided into two main reservoirs: (a) a superficial aquifer which basically follows the volcanic structure morphology and tectonics and (b) a deeper reservoir, originating within the oldest Roccamonfina volcano ultra potassic lavas and then flowing into the carbonate aquifers of the neighboring plain. Eventually, the chemistry of the Roccamonfina aquifer does not show any specific and visible pollution, contrary to what happens in the volcano surrounding plains. In fact, only 14% of the samples we collected (206) show a NO₃ content >30 mg/l. These sites are all located at the base of the volcano, near the plain.     

Evaluation of building fundamental periods and effects of local geology on ground motion parameters in the Siracusa area,Italy

The Siracusa area, located in the southeastern coast of Sicily (Italy), is mainly characterized by the outcropping of a limestone formation. This lithotype, which is overlain by soft sediments such as sandy clays and detritus, can be considered as the local bedrock. Records of ambient noise, processed through spectral ratio techniques, were used to assess the dynamic properties of a sample survey of both reinforced concrete and masonry buildings. The results show that experimental periods of existing buildings are always lower than those proposed by the European seismic code. This disagreement could be related to the role played by stiff masonry infills, as well as the influence of adjacent buildings, especially in downtown Siracusa. Numerical modeling was also used to study the effect of local geology on the seismic site response of the Siracusa area. Seismic urban scenarios were simulated considering a moderate magnitude earthquake (December 13th, 1990) to assess the shaking level of the different outcropping formations. Spectral acceleration at different periods, peak ground acceleration, and velocity were obtained through a stochastic approach adopting an extended source model code. Seismic ground motion scenario highlighted that amplification mainly occurs in the sedimentary deposits that are widespread to the south of the study area as well as on some spot areas where coarse detritus and sandy clay outcrop. On the other hand, the level of shaking appears moderate in all zones with outcropping limestone and volcanics.     

Pre-alpine and alpine evolution of the South-alpine basement of the Orobic Alps

New K-Ar age determinations on the gneisses and schists of the south-Alpine basement of the Orobic Alps and their separated minerals have been carried out to supplement and support the previous study ofBocchio et al. (1981).The cooling ages of biotites and muscovites range from 218 to 331 my and from 170 to 330 my respectively, according to a bimodal distribution with modes at 222 and 298 my for biotite, 182 and 322 my for muscovite. The whole rock ages spread from 43 to 402 my with no significant cluster. Only a few samples give statistically significant internal isochrones, and these suggest two periods of equilibration, at 226–245 and 312–368 my.These age determinations support the conclusion drawn from regional petrologic studies (Bocchio et al., 1980;Crespi et al., 1980), that the south-Alpine basement underwent two main phases of metamorphism, now preferentially preserved in different areas: an old, Hercynian phase under a regime of intermediate pressure (staur-ky type), and a young, post-Hercynian phase under a regime of low pressure (staur-sill type) reactivated by the cover of the thick sedimentary pile on top of the basement. Furthermore, radiometric ages also point out the widespread but irregularly distributed occurence of an alpine overprint under the conditions of a very low metamorphic regime, that is documented by the growth of post-kinematic stilpnomelane in rocks of suitable bulk composition (Crespi et al., 1981, 1982), as well as by fine-grained phengite.

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Zusammenfassung Neue Kali-Argon-Datierungen von Gneisen und Schiefern und ihrer abgetrennten Minerale des südalpinen Grundgebirges wurden in Ergänzung der Studie vonBocchio et al., 1981 durchgeführt. Die Abkühlungsalter der Biotite und Muskovite reichen von 218 bis 331 ma und von 170 bis 330 ma entsprechend einer bimodalen Entwicklung mit Modalwerten bei 222 und 298 ma für Biotit und 182 und 322 ma für Muskovit. Die Gesamtgesteinsalter reichen von 43–402 ma ohne signifikante Häufung. Nur wenige Proben geben eine statistisch signifikante Isochrone, woraus sich zwei Gleichgewichtsperioden zwischen 226–245 ma und 312–368 ma ablesen lassen.Diese Altersbestimmungen unterstützen die Schlußfolgerungen, die aus regional-petrologischen Studien (Bocchio et al., 1980;Crespi et al., 1980) gezogen wurden und die Aussagen, daß das südalpine Grundgebirge zwei Hauptphasen der Metamorphose mitgemacht hat, die heute in verschiedenen Gebieten erhalten sind: eine ältere herzynische Phase unter mittleren Druckbedingungen (Staur-Ky) und eine jüngere postherzynische Phase unter niedrigem Druck (Staur-Sil), die unter der Überdeckung einer mächtigen Sedimentserie über dem Grundgebirge reaktiviert wurde. Darüber hinaus deuten die radiometrischen Alter auf einen weit verteilten, aber unregelmäßig auftretenden alpinen Einfluß hin, der unter den Bedingungen einer sehr niedrigen Metamorphose aufgeprägt wurde. Dies wird dokumentiert durch das Wachstum postkinematischer Stilpnomelane in Gesteinen mit einer entsprechenden Zusammensetzung (Crespi et al., 1981, 1982) sowie von feinkörnigen Phenigiten.

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Résumé De nouvelles déterminations d'âge par la méthode K-Ar ont été effectuées sur les gneiss et les schistes du socle sudalpin des Alpes Orobiques, ainsi que sur certains de leurs minéraux, en complément aux travaux antérieurs deBocchio et al. (1981).L'âge du refroidissement des biotites s'étend de 210 à 331 Ma et celui des muscovites de 170 à 330 Ma, selon une distribution bimodale: modes à 222 à 298 Ma pour la biotite et à 183 et 322 Ma pour la muscovite. Les âges mesurés sur roche totale vont de 43 à 402 Ma sans concentration significative autour d'une valeur. Un petit nombre d'échantillons seulement fournissent des isochrones statistiquement significatives; elles suggèrent deux périodes de mise en équilibre, à 226–245 Ma et à 312–368 Ma.Ces déterminations d'âge appuient les conclusions d'études pétrologiques régionales antérieures (Bocchio et al. 1980;Crespi et al. 1980), à savoir que le socle sud-alpin a subi deux phases principales de métamorphisme, conservées aujourd'hui dans de régions différentes: une phase ancienne, hercynienne, de pression intermédiaire (type staurotide-disthène) et une phase jeune, post-hercynienne, de basse pression (type staurotide-sillimanite) réactivée sous la couverture sédimentaire épaisse reposant sur le socle. De plus, les âges radiométriques mettent en évidence une reprise alpine, d'extension régionale mais irrégulièrement distribuée, dans les conditions d'un métamorphisme de très faible degré. Cette reprise s'exprime par la croissance de stilpnomélane post-cinématique dans les roches de composition appropriée (Crespi et al. 1981, 1982) ainsi que par le développement de phengite finement grenue.

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. (1981), K/Ar-. 218 331 170 330 , 222 298 182 322 . 43–402 - . , 226–245 312–368 . . (1980) . (1980) , - : , , (Staur-Ky) , , (StaurSil) , . , , . ( ., 1981, 1982), .

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Paper presented at the Second E.U.G. Meeting at Strasbourg, April 23–26, 1983     

Fault geometries from the space distribution of the 1990–1997 Sannio–Benevento earthquakes: inferences on the active deformation in Southern Apennines

In this study, we analyze the recent (1990–1997) seismicity that affected the northern sector (Sannio–Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method (BEM), which collapses hypocentral clouds, to the events of low energy (M_{d max}=4.1) seismic sequences in order to constrain the location and geometry of the seismogenetic structures. The results indicate that earthquakes aligned along three main structures: two sub-parallel structures striking NW–SE (1990–1992, Benevento sequence) and one structure striking NE–SW (1997, Sannio sequence). The southernmost NW–SE structure, which dips towards NE, overlies the fault that is likely to be responsible for a larger historical earthquake (I_{o max}=XI MCS, 1688 earthquake). The northernmost NW–SE striking structure dips towards SW. The NE–SW striking structure is sub-vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake. The spatio-temporal evolution of the 1990–1997 seismicity indicates a progressive migration from SE (Benevento) to NW (Sannio) associated to a deepening of hypocenters (i.e., from about 5 to 12 km). Hypocenters cluster at the interface between the major structural discontinuities (e.g., pre-existing thrust surfaces) or within higher rigidity layers (e.g., the Apulia carbonates). Available focal mechanisms from earthquakes occurred on the recognized NW–SE and NE–SW faults are consistent with dip-slip normal solutions. This evidences the occurrence of coexisting NW–SE and NE–SW extensions in Southern Apennines.     

Geology of the Murcia Valley and Flood Plain Modifications in the Construction of the Circus Maximus,Rome, Italy

This paper presents a morphological and hydrogeological reconstruction of the Murcia Valley at the location of the great Roman stadium Circus Maximus in Rome. We reconstruct a valley segment using ERT (electrical resistivity tomography) and geoarchaeological drilling data that identified three main layers. The basal layer, with high resistivity values and convex shapes, is correlated to alluvial gravel and lithified silt‐clay sediments. The middle layer shows low‐to‐medium resistivity values extending to concavities between the basal convex shapes. The very low resistivity values of this middle layer characterize elliptical to circular morphologies and have been ascribed to the presence of water‐saturated clay‐silt and peaty sediments. The surface layer is characterized by widespread lateral inhomogeneity interpreted as anthropogenic fill. The data indicate a pre‐Roman anastomosed alluvial plain subsequently modified by human intervention. In an effort to reclaim the valley for construction of the Circus, the Romans utilized the natural topography and created a central embankment, later becoming the Spina, by filling depressions with sand taken from adjacent bars. Our study contributes to (1) knowledge of the pre‐Roman landscape, (2) understanding anthropogenic modification of the Murcia Valley flood plain, and (3) archaeological interpretation of the monument.