Predicted ground motion after the L��Aquila 2009 earthquake (Italy, M w 6.3): input spectra for seismic microzoning

After the April 6th 2009 L’Aquila earthquake (M _w 6.3), where 306 people died and a further 60,000 were displaced, seismic microzoning investigations have been carried out for towns affected by a macroseismic intensity equal to or greater than 7 MCS. Based upon seismotectonic data, historical seismicity and strong motion records, we defined input spectra to be used in the numerical simulations of seismic microzoning in four key municipalities, including the town of L’Aquila. We adopted two main approaches: uniform hazard response spectra are obtained by a probabilistic seismic hazard assessment introducing some time-dependency for individual faults on the study area; a deterministic design spectrum is computed from magnitude/distance pairs extracted by a stationary probabilistic analysis of historical intensities. The uniform hazard spectrum of the present Italian building code represents the third, less restrictive, response spectrum to be used for the numerical simulations in seismic microzoning. Strong motions recordings of the main shock of the L’Aquila sequence enlighten the critical role played by both the local response and distances metric for sites located above a seismogenic fault; however, these time-histories are compatible with the uncertainties of a deterministic utilization of ground motion predictive equations. As recordings at very near field are rare, they cannot be neglected while defining the seismic input. Disaggregation on the non-Possonian seismotectonic analysis and on the stationary site-intensity estimates reach very similar results in magnitude-distance pairs identification; we interpret this convergence as a validation of the geology-based model by historical observations.     

Central Mediterranean tephrochronology between 313 and 366 ka: New insights from the Fucino palaeolake sediment succession

Thirty-two tephra layers were identified in the time-interval 313–366 ka (Marine Isotope Stages 9–10) of the Quaternary lacustrine succession of the Fucino Basin, central Italy. Twenty-seven of these tephra layers yielded suitable geochemical material to explore their volcanic origins. Investigations also included the acquisition of geochemical data of some relevant, chronologically compatible proximal units from Italian volcanoes. The record contains tephra from some well-known eruptions and eruptive sequences of Roman and Roccamonfina volcanoes, such as the Magliano Romano Plinian Fall, the Orvieto–Bagnoregio Ignimbrite, the Lower White Trachytic Tuff and the Brown Leucitic Tuff. In addition, the record documents eruptions currently undescribed in proximal (i.e. near-vent) sections, suggesting a more complex history of the major eruptions of the Colli Albani, Sabatini, Vulsini and Roccamonfina volcanoes between 313 and 366 ka. Six of the investigated tephra layers were directly dated by single-crystal-fusion ⁴⁰Ar/³⁹Ar dating, providing the basis for a Bayesian age–depth model and a reassessment of the chronologies for both already known and dated eruptive units and for so far undated eruptions. The results provide a significant contribution for improving knowledge on the peri-Tyrrhenian explosive activity as well as for extending the Mediterranean tephrostratigraphical framework, which was previously based on limited proximal and distal archives for that time interval.     

Vertumnite,a new natural silicate

Summary A natural calcium aluminum silicate hydrate, vertumnite, is described as a new mineral. It has been found as transparent flattened hexagonal prisms resting on a layer of tobermorite inside a subspherical geode of a phonolite from a quarry at Campomorto, Montalto di Castro, Viterbo, Italy. Most of the crystals are biaxial negative and twinned. The single crystal measurements on an optically homogeneous and biaxial individual gave:a=0.5744 (5) nm,b=0.5766(5) nm,c=2.512(1) nm, =119.72(5)° and space groupP2₁/m orP2₁. The optical properties are:n =1.531(1),n =1.535(1),n =1.541(2) and 2V =62°. The chemical formula is: (Na_0.02K_0.02Ca_3.76Sr_0.06Ba_0.01)_tot=3.87 Al_4.36(P_0.03Si_3.38)_tot=3.41O_5.18 (OH)_24.66·3.09H₂O or schematically Ca₄Al₄Si₄O₆(OH)₂₄ ·3 H₂O. Both the powder data and chemical analysis suggest the mineral to be stronghly related to the synthetic Strätling's compound or hexagonal hydrated gehlenite although the different Si/Al ratios in two inhibit direct correlations.

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Vertumnit, ein neues natürliches Silikat

Zusammenfassung Ein natürliches, wasserhaltiges Calcium-Aluminium-Silikat, Vertumnit, wird als neues Mineral beschrieben. Es kommt in durchsichtigen, flachen, hexagonalen Prismen vor, die auf einer Tobermorit-Schicht in einer kugeligen Geode eines Phonoliths einer Grube in Campomorto, Montalto di Castro, Viterbo, Italien, gefunden wurden. Die meisten Kristalle sind zweiachsig negativ und verzwillingt. Einkristallmessungen an einem optisch homogenen und zweiachsigen Individuum ergaben:a=0,5744(5) nm,b=0,5766(5) nm,c=2.512(1) nm, =119.72(5)° mit RaumgruppeP2₁/m oderP2₁. Die optische Eigenschaften sind wie folgt:n =1,531(1),n =1,535(1),n =1,541(2), 2V =62°. Die chemische Formel ist: (Na_0.02K_0.02Ca_3.76Sr_0.06Ba_0.01)_tot=3.87Al_4.36(P_0.03Si_3.38)_tot=3.41 O_5.18(OH)_24.66·3,09 H₂O oder schematisch Ca₄Al₄Si₄O₆(OH)₂₄·3 H₂O. Sowohl die Pulverdaten als auch die chemische Analyse weisen auf eine Verwandtschaft mit der Strätling-Verbindung oder hexagonal hydrated gehlenite hin, obwohl die verschiedenen Si/Al-Verhältnisse in beiden direkte Beziehungen verhindern.

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With 3 Figures     

On the persistence of the 22 y solar cycle

We briefly discuss the existence of precise periodicities of the Hale cycle (-22 y), the Gleissberg cycle (-88 y), and -132 y cycle, in various direct and indirect indicators (as aurorae, ¹⁴C from tree rings and ¹⁰Be from polar ice) of solar activity. We consider also the behaviour of the 11y cycle and its first harmonic in modern sunspot series. It appears that the frequencies of -1 c/88 y and -1 c/132 y might be two subharmonics of the Hale cycle. The results support the hypothesis that the Sun behaves as a nonlinear system forced by an oscillator having the Hale frequency. The forcing element inside the Sun can be identified with a magnetofluid torsional oscillator.     

Stratigraphic evolution of the Triassic–Jurassic succession in the Western Southern Alps (Italy): the record of the two-stage rifting on the distal passive margin of Adria

The Triassic–Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break‐up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre‐Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian–Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian–Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian–Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian–Toarcian boundary. This younger rift bridges the gap between the Hettangian–Sinemurian diffuse rifting and the Callovian–Bathonian break‐up. The late Pliensbachian–Toarcian rift, which eventually lead to continental break‐up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins.