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<strong>First</strong> <strong>International</strong> <strong>Conference</strong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE 16-19 May 2012, Bacau, Romania THE RELEVANCE OF VOLCANIC HAZARD IN ROMANIA: IS THERE ANY?" Szakács Alexandru 1, 2 , Seghedi Ioan 2 1 Sapientia University, Dept. of Environmental Sciences, Cluj-Napoca, Romania, 2 Institute of Geodynamics, Romanian Academy, Bucharest, Romania Szakács Alexandru, szakacs@sapientia.ro Abstract: Volcanic hazard is ignored in natural hazard studies in Romania because no active volcano is known on its territory. However, the 2010 eruption of Eyjafjallajökull volcano in Iceland and its consequences on air traffic safety across Europe and the whole northern hemisphere dramatically demonstareted that volcanic hazard in a certain area, such as a country, is not necessarily related to the presence of active volcanoes in the same territory. Therefore, target-centered approaches to volcanic hazard should also consider remotely located hazard sources with respect the target territory. This study aims at compiling an inventory of potential volcanic hazard sources for the territory of Romania, irrespective of their location inside or outside the country. External volcanic sources implying ash-fall hazard from tepha dispersion following explosive volcanic eruptions include the Central Italian field of active volcanoes (e.g. Campii Flegreii and Vesuvius), the active Eagean volcanic arc (Greece), the Eifel region of Central Europe (Germany), and Iceland. Geologic evidence of thick tephra deposition from Campii Flegrei caldera (its Campanian ignimbite eruption ca. 39 Ka ago) found in southern Romania clearly indicates that such type of volcanic hazard is real. On the other hand, study of the most recent volcanic activity in Romania shows that the last eruptive event, of explosive plinian type, occurred at Ciomadul volcano at the south-eastern end of the Călimani-Gurghiu-Harghita (CGH) volcanic range (East Carpathians) in a poorly-constrained time interval of 10.7 to 35 Ka in the continuation of a ca. 10.5 Ma southward-shifting volcanic activity along the whole CGH range. A number of peculiar features of the Ciomadul volcano and its environs strongly suggest that the magma pumbing system of this volcano is not definitely frozen: a well-focused and strongest-in-Romania heat-flow anomaly, crustal and sub-crustal local seismic activity, seismic wave attenuation patterns recorded in seismic tompography images, most intense “post-volcanic activity” including mantle-originated gas emanations. Al these symptoms allow one to consider that future eruptions from this volcano cannot be ruled out. Dedicated geophysical studies are needed to obtain more basic information on the current status of the magma-generating and plumbing systems of Ciomadul volcano, which is crucial from the viewpoint of volcanic hazard assesment. Key words: Volcanic hazard, East Carpathians, Ciomadul volcano, explosive eruption, tephra. 34
<strong>First</strong> <strong>International</strong> <strong>Conference</strong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE 16-19 May 2012, Bacau, Romania UPPER MANTLE STRUCTURES BENEATH THE CARPATHIAN-PANNONIAN REGION: IMPLICATIONS FOR ITS GEODYNAMICS Yong Ren 1 , Graham W. Stuart 1 , Gregory A. Houseman 1 , Ben Dando 2 , Constantin Ionescu 3 , Endre Hegedüs 4 , Slavica Radovanović 5 , Yang Shen 6 , South Carpathian Project working group 1 School of Earth and Environment, University of Leeds, LS2 9JT, Leeds, UK; 2 RockTalk Imaging Ltd, Chacewater, Cornwall TR4 8PN, UK 3 National Institute of Earth Physics, Bucharest, Romania 4 Eötvös Loránd Geophysical Institute, Budapest, Hungary 5 Seismological Survey of Serbia, Belgrade, Serbia 6 Graduate School of Oceanography, University of Rhode Island, USA Corresponding author: Yong Ren, earyr@leeds.ac.uk Abstract: The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence and extension and convective processes in the upper mantle. Here, we present high-resolution images of upper mantle structure beneath the region obtained using P- and S-wave finite-frequency teleseismic tomography to help constrain the geodynamical interpretation of the region. We have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. The data were recorded on 57 temporary stations deployed in the South Carpathian Project (2009-2011), 56 temporary stations deployed in the Carpathian Basins Project (2005-2007), and 131 permanent broadband stations of national networks. The relative arrival times are measured in high and intermediate frequency bands (0.5-2.0 Hz and 0.1-0.5 Hz for Pwaves, 0.1-0.5 Hz and 0.05-0.1 Hz for S-waves), and are inverted to produce P- and Swave velocity maps in the upper mantle. Our images show a sub-vertical slab of fast material beneath the eastern Alps which extends eastward across the Pannonian basin at depths below ~300 km. The fast material extends down into the mantle transition zone (MTZ), where it spreads out beneath the entire basin. Above ~300 km, the upper mantle below the Pannonian basin is dominated by relatively slow velocities, the largest of which extends down to ~200 km and underlies the >7km thick sediments of the Mako-Békés rift basins. We suggest that cold mantle lithospheric downwelling occurred below the Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone, intermediatedepth seismicity occurs at the NE end of an upper mantle high velocity structure that extends SW oblique to the southern edge of the South Carpathians. This sub-vertical highvelocity body is bounded by slow anomalies to the NW and SE, which extend down to the top of the MTZ. No clear evidence of residual slabs is observed in the mid upper mantle beneath Eastern Carpathians; the eastern Carpathians are underlain by slow velocities everywhere above the transition zone. These observations suggest that intermediate depth seismicity in the Vrancea Zone is unlikely to be due to slab tearing, but rather could be explained by either gravitational instability or delamination of mantle lithosphere. 35
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