Concurrent eruptions at Etna, Stromboli, and Vulcano: casualty or causality?

Anecdotes of concurrent eruptions at Etna, Stromboli, and Vulcano (Southern Italy) have persisted for more than 2000 years and volcanologists in recent and past times have hypothesized a causal link among these volcanoes. Here this hypothesis is tested. To introduce the problem and provide examples of the type of expected volcanic phenomena, narratives of the most notable examples of concurrent eruptions are provided. Then the frequency of eruptions at each individual volcano is analysed for about the last 300 years and the expected probability of concurrent eruptions is calculated to compare it to the observed probability. Results show that the occurrence of concurrent eruptions is often more frequent than a random probability, particularly for the Stromboli-Vulcano pair. These results are integrated with a statistical analysis of the earthquake catalogue to find evidence of linked seismicity in the Etnean and Aeolian areas. Results suggest a moderate incidence of non-random concurrent eruptions, but available data are temporally limited and do not allow an unequivocal identification of plausible triggers; our results, however, are the first attempt to quantify a more-than-2000-years-old curious observation and constitute a starting point for more sophisticated analyses of new data in the future. We look forward to our prediction of a moderate incidence of concurrent eruptions being confirmed or refuted with the passage of time and occurrence of new events

Subduction Duration and Slab Dip

The dip angles of slabs are among the clearest characteristics of subduction zones, but the factors that control them remain obscure. Here, slab dip angles and subduction parameters, including subduction duration, the nature of the overriding plate, slab age, and convergence rate, are determined for 153 transects along subduction zones for the present day. We present a comprehensive tabulation of subduction duration based on isotopic ages of arc initiation and stratigraphic, structural, plate tectonic and seismic indicators of subduction initiation. We present two ages for subduction zones, a long‐term age and a reinitiation age. Using cross correlation and multivariate regression, we find that (1) subduction duration is the primary parameter controlling slab dips with slabs tending to have shallower dips at subduction zones that have been in existence longer; (2) the long‐term age of subduction duration better explains variation of shallow dip than reinitiation age; (3) overriding plate nature could influence shallow dip angle, where slabs below continents tend to have shallower dips; (4) slab age contributes to slab dip, with younger slabs having steeper shallow dips; and (5) the relations between slab dip and subduction parameters are depth dependent, where the ability of subduction duration and overriding plate nature to explain observed variation decreases with depth. The analysis emphasizes the importance of subduction history and the long‐term regional state of a subduction zone in determining slab dip and is consistent with mechanical models of subduction

Shear-Velocity Structure and Dynamics Beneath the Sicily Channel and Surrounding Regions of the Central Mediterranean Inferred From Seismic Surface Waves

The evolution of the Sicily Channel Rift Zone (SCRZ) is thought to accommodate the regional tectonic stresses of the Calabrian subduction system. Much of the observations we have today are either limited to the surface or to the upper crust or deeper from regional seismic tomography, missing important details about the lithospheric structure and dynamics. It is unclear whether the rifting is passive from far-field extensional stresses or active from mantle upwelling beneath. We measure Rayleigh-and Love-wave phase velocities from ambient seismic noise and invert for 3-D shear-velocity and radial anisotropic models. Variations in crustal S-velocities coincide with topographic and tectonic features. The Tyrrhenian Sea has a ∼10 km thin crust, followed by the SCRZ (∼20 km). The thickest crust is beneath the Apennine-Maghrebian Mountains (∼55 km). Areas experiencing extension and intraplate volcanism have positive crustal radial anisotropy (VSH > VSV); areas experiencing compression and subduction-related volcanism have negative anisotropy. The crustal anisotropy across the Channel shows the extent of the extension. Beneath the Tyrrhenian Sea, we find very low sub-Moho S-velocities. In contrast, the SCRZ has a thin mantle lithosphere underlain by a low-velocity zone. The lithosphere-asthenosphere boundary rises from 60 km depth beneath Tunisia to ∼33 km beneath the SCRZ. Negative radial anisotropy in the upper mantle beneath the SCRZ is consistent with vertical mantle flow. We hypothesize a more active mantle upwelling beneath the rift than previously thought from an interplay between poloidal and toroidal fluxes related to the Calabrian slab, which in turn produces uplift at the surface and induces volcanism

A Multidisciplinary Approach to Earthquake Research: Implementation of a Geochemical Geographic Information System for the Gargano Site, Southern Italy

A priority task for correct environmental planning is to evaluate Natural Hazards, especially in highly populated areas. In particular, thorough investigations based on different Earth Science techniques must be addressed for the Seismic Hazard Assessment (SHA) in tectonically active areas. Not only the management but also the multidisciplinary analysis of all the SHA-related data sets is best performed using a Geographic Information System. In this paper we show how a researchoriented GIS is built and used in a practical case. The Geochemical Geographic Information System (G2IS) was developed and applied to the Gargano promontory (southern Italy) in the framework of an EC research project, the Geochemical Seismic Zonation (GSZ) Project. This multidisciplinary – multiscaling powerful tool is described in its structure, updating procedures and manipulation techniques. Preliminary results are presented on the detection of geochemically active fault zones and their correlation with remote sensing data and other evidences of seismogenic structures.Published255-278JCR Journalreserve

Assessing the volcanic hazard for Rome. 40Ar/39Ar and In-SAR constraints on the most recent eruptive activity and present-day uplift at Colli Albani Volcanic District

We present new 40Ar/39Ar data which allow us to refine the recurrence time for the most recent eruptive activity occurred at Colli Albani Volcanic District (CAVD) and constrain its geographic area. Time elapsed since the last eruption (36 kyr) overruns the recurrence time (31 kyr) in the last 100 kyr. New interferometric synthetic aperture radar data, covering the years 1993–2010, reveal ongoing inflation with maximum uplift rates (>2 mm/yr) in the area hosting the most recent (<200 ka) vents, suggesting that the observed uplift might be caused by magma injection within the youngest plumbing system. Finally, we frame the present deformation within the structural pattern of the area of Rome, characterized by 50 m of regional uplift since 200 ka and by geologic evidence for a recent (<2000 years) switch of the local stress-field, highlighting that the precursors of a new phase of volcanic activity are likely occurring at the CAVD

Archaeoseismology: Methodological issues and procedure

Archaeoseismic research contributes important data on past earthquakes. A limitation of the usefulness of archaeoseismology is due to the lack of continuous discussion about the methodology. The methodological issues are particularly important because archaeoseismological investigations of past earthquakes make use of a large variety of methods. Typical in situ investigations include: (1) reconstruction of the local archaeological stratigraphy aimed at defining the correct position and chronology of a destruction layer, presumably related to an earthquake; (2) analysis of the deformations potentially due to seismic shaking or secondary earthquake effects, detectable on walls; (3) analysis of the depositional characteristics of the collapsed material; (4) investigations of the local geology and geomorphology to define possible natural cause(s) of the destruction; (5) investigations of the local factors affecting the ground motion amplifications; and (6) estimation of the dynamic excitation, which affected the site under investigation. Subsequently, a 'territorial' approach testing evidence of synchronous destruction in a certain region may delineate the extent of the area struck by the earthquake. The most reliable results of an archaeoseismological investigation are obtained by application of modern geoarchaeological practice (archaeological stratigraphy plus geological–geomorphological data), with the addition of a geophysical-engineering quantitative approach and (if available) historical information. This gives a basic dataset necessary to perform quantitative analyses which, in turn, corroborate the archaeoseismic hypothesis. Since archaeoseismological investigations can reveal the possible natural causes of destruction at a site, they contribute to the wider field of environmental archaeology, that seeks to define the history of the relationship between humans and the environment. Finally, through the improvement of the knowledge on the past seismicity, these studies can contribute to the regional estimation of seismic hazard