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Ren Y.,University of Leeds | Grecu B.,National Institute of Materials Physics Bucharest | Stuart G.,University of Leeds | Houseman G.,University of Leeds | And 29 more authors.
Geophysical Journal International | Year: 2013

We use ambient noise tomography to investigate the crust and uppermost mantle structure beneath the Carpathian-Pannonian region of Central Europe. Over 7500 Rayleigh wave empirical Green's functions are derived from interstation cross-correlations of vertical component ambient seismic noise recordings (2005-2011) using a temporary network of 54 stations deployed during the South Carpathian Project (2009-2011), 56 temporary stations deployed in the Carpathian Basins Project (2005-2007) and 100 permanent and regional broad-band stations. Rayleigh wave group velocity dispersion curves (4-40 s) are determined using the multiple-filter analysis technique. Group velocity maps are computed on a grid of 0.2° × 0.2° from a non-linear 2-D tomographic inversion using the subspace method. We then inverted the group velocity maps for the 3-D shear wave velocity structure of the crust and uppermost mantle beneath the region. Our shear wave velocity model provides a uniquely complete and relatively high-resolution view of the crustal structure in the Carpathian-Pannonian region, which in general is validated by comparison with previous studies using other methods to probe the crustal structure. At shallow depths (<10 km) we find relatively high velocities below where basement is exposed (e.g. Bohemian Massif, Eastern Alps, most of Carpathians, Apuseni Mountains and Trans-Danubian Ranges) whereas sedimentary areas (e.g. Vienna, Pannonian, Transylvanian and Foçsani Basins) are associated with low velocities of well defined depth extent. The mid to lower crust (16-34 km) below the Mid-Hungarian Line is associated with a broad NE-SW trending relatively fast anomaly, flanked to the NW by an elongated low-velocity region beneath the Trans-Danubian Ranges. In the lowermost crust and uppermost mantle (between 30 and 40 km), relatively low velocities are observed beneath the Bohemian Massif and Eastern Alps but the most striking features are the broad low velocity regions beneath the Apuseni Mountains and most of the Carpathian chain, which likely is explained by relatively thick crust. Finally, most of the Pannonian and Vienna Basin regions at depths >30 km are relatively fast, presumably related to shallowing of the Moho consequent on the extensional history of the Pannonian region. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Pavel F.,Technical University of Civil Engineering Bucharest | Vacareanu R.,Technical University of Civil Engineering Bucharest | Douglas J.,University of Strathclyde | Radulian M.,National Institute of Earth Physics NIEP | And 3 more authors.
Pure and Applied Geophysics | Year: 2016

The probabilistic seismic hazard analysis for Romania is revisited within the framework of the BIGSEES national research project (http://infp.infp.ro/bigsees/default.htm) financed by the Romanian Ministry of Education and Scientific Research in the period 2012–2016. The scope of this project is to provide a refined description of the seismic action for Romanian sites according to the requirements of Eurocode 8. To this aim, the seismicity of all the sources influencing the Romanian territory is updated based on new data acquired in recent years. The ground-motion models used in the analysis, as well as their corresponding weights, are selected based on the results from several recent papers also published within the framework of the BIGSEES project. The seismic hazard analysis for Romania performed in this study are based on the traditional Cornell-McGuire approach. Finally, the results are discussed and compared with the values obtained in the recently completed SHARE research project. The BIGSEES and SHARE results are not directly comparable since the considered soil conditions are different—actual soil classes for BIGSEES and rock for SHARE. Nevertheless, the analyses of the seismic hazard results for 200 sites in Romania reveal considerable differences between the seismic hazard levels obtained in the present study and the SHARE results and point out the need for further analyses and thorough discussions related to the two seismic hazard models, especially in the light of a possible future harmonized hazard map for Europe. © 2015, Springer International Publishing.

Marmureanu G.,National Institute of Earth Physics NIEP | Cioflan C.O.,National Institute of Earth Physics NIEP | Manea E.F.,National Institute of Earth Physics NIEP
Geotechnical, Geological and Earthquake Engineering | Year: 2015

In seismic hazard evaluation and risk mitigation, there are many random and epistemic uncertainties. On the another hand, the researches in this area as part of knowledge are with rest, that is, the results are with interpretable questions with open answers. The knowledge cannot be exhausted by results. The authors developed in last time the concept of “Nonlinear Seismology – The Seismology of the XXI Century” (Marmureanu et al. Nonlinear seismology-the seismology of XXI century. In: Modern seismology perspectives, vol 105. Springer, New York, pp 49–70, 2005). The leading question is: how many cities, villages, metropolitan areas, etc., in seismic regions are constructed on rock? Most of them are located on soil deposits. A soil is of basic type sand or gravel (termed coarse soils), silt or clay (termed fine soils), etc. Strong ground accelerations from large earthquakes can produce a nonlinear response in shallow soils. This can be studied by comparing surface and borehole seismic records for earthquakes of different sizes. When a nonlinear site response is present, then the shaking from large earthquakes cannot be predicted by simple scaling of records from small earthquakes (Shearer, Introduction to seismology, 2nd edn. Cambridge University Press, Cambridge, 2009). Nonlinear amplification at sediments sites appears to be more pervasive than seismologists used to think. . .Any attempt at seismic zonation must take into account the local site condition and this nonlinear amplification (Aki, Tectonophysics 218:93–111, 1993). © The Author(s) 2015.

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