First International Conference on MOLDAVIAN RISKS – FROM ...

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ong>Firstong> ong>Internationalong> ong>Conferenceong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE 16-19 May 2012, Bacau, Romania WHY IT IS SO HARD TO ASSESS LANDSLIDES’ HAZARD AND RISK IN ROMANIA? Raluca-Mihaela Maftei, Constantina Filipciuc Geological Institute of Romania Corresponding author: Raluca-Mihaela Maftei, mafteir@yahoo.com Abstract: The idea of presenting this paper appeared after reading the article of C.J. van Westen et al., from 2005, concerning the difficulties encountered in assessing hazard and risk to landslide. As Romania is located in Europe as one of first places, unfortunately, regarding the effect of these phenomena, we considered appropriate to deal with the subject. According to van Westen, even though in recent years the literature has shown a development in hazard and risk estimation with geotechnics, by in situ investigations, development of hazard maps and risk assessment to landslides, procedures absolutely necessary for regulatory and development planning by authorities, this actions still remain a far end goal, especially to medium scale (1:10.000- 1:50.000). In this article we try to illustrate the difficulties encountered in our attempt to develop landslide hazard maps at a regional scale. Thus, we present the difficulties arising in the inventory of this kind of phenomena, including information on the occurrence, type and volume of landslides, establishment of spatial and temporal probability of release, vulnerability assessment etc. In light of the above, we illustrate the hazard maps developed by our team, presenting hence the problems we faced. The major issues to be solved did not regard legislation, which is by far thick, but access to the necessary information to elaborate maps, according to the Methodological Norms in Force, uncertainty about quality and accuracy of these information and the list may go on. Key words: landslide hazard, vulnerability, spatial and temporal probability. 32

ong>Firstong> ong>Internationalong> ong>Conferenceong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE 16-19 May 2012, Bacau, Romania PLIO-PLEISTOCENE CONNECTION BETWEEN THE ‘VRANCEA ZONE’ AND THE SOUTHERN END OF THE HARGHITA VOLCANIC CHAIN Seghedi Ioan 1 1, 2 , Szakács Alexandru 1 Institute of Geodynamics, Romanian Academy, Bucharest, Romania 2 Sapientia University, Dept. of Environmental Sciences, Cluj-Napoca, Romania Seghedi Ioan, seghedi@geodin.ro Abstract: Miocene convergence at ~ 11 Ma of the Eastern Carpathian orogen of Romania caused the tectonic nappes emplacement of the fold - thrust belt. The following postcollisonal complex tectonic crustal deformation in this area resulted in Late Miocene to Quaternary formation of the Cǎlimani-Gurghiu-Harghita volcanic chain. This was possibly related to clockwise rotation and front block-fragmentation of the inner Carpathian (Dacia) crustal block. The Carpathian foreland is characterized by a mechanically strong and cold European-Scythian Plate welded to the south with weak Moesian plate along the Trotuş transverse high angle basement fault system that was reactivated and decoupled from it during Late Pliocene-Quaternary. This period was characterized by differential vertical movements of the Moesian plate associated with ~5km of contraction restricted roughly between the Trotuş and Intramoesian faults and sustained by the apparently folded, shallow Moho beneath the orogen and the generation of ‘Vrancea zone’. In the same period after a time gap Plio-Quaternary magmatic activity in the interior of the Carpathians area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to a diverse compositions (adakite-like calc-alkaline, K-alkalic, in South Harghita Mountains and mafic Na-alkalic in Perşani Mountains). This magmatism is interpreted to be in close connection to steepening of ‘Vrancea zone’ via tearing or delamination of its eclogitic keel and partial melting of this material at mantle depths to explain the peculiar chemistry of adakite-like volcanic rocks as a consequence of elevated K2O/Na2O in the protolith and high pressure conditions of partial melting. The surface projection of the South Harghita adakite-like calc-alkaline volcanism at the edge of ‘Vrancea zone’, as a piece of metasomatised lithosphere can be explained by its heating and partial melting during the horizontal asthenospheric flow around the steepening zone. The Na-alkalic mafic magmas were derived from such an uprised asthenospheric mantle-source by decompression melting that correlates with a low-velocity anomaly and with a high attenuation volume, as indicated by the geophysical observations. Generation of K and Na alkalic magmas in the similar time interval, by interrupting the adakite-like volcanism signifies changes in the source and melting mechanism by renewed contraction associated with deep mantle processes facilitated by the generalized tectonic inversion event which started during the latest Pliocene in the whole Carpathian–Pannonian region. Key words: Post-collisional magmatism, slab mechanics, calc-alkaline adakite magmas, K and Na alkalic magmas. 33

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