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Dando B.D.E.,University of Leeds | Stuart G.W.,University of Leeds | Houseman G.A.,University of Leeds | Hegedus E.,Eotvos Lorand Geophysical Institute | And 2 more authors.
Geophysical Journal International | Year: 2011

Subducted slab roll-back, lithospheric instability and asthenospheric extrusion have all been proposed as mechanisms that explain the evolution of the extensional Pannonian Basin, within the convergent arc of the Alpine-Carpathian mountain system in central Europe. We determine the P- and S-wave velocity structure of the mantle to depths of 850km beneath this region using tomographic inversion of relative arrival-time residuals from 225 (P waves) and 124 (S waves) teleseismic earthquakes recorded by 56 stations of the Carpathian Basins Project (CBP) temporary seismic network (16-month duration) and 44 permanent seismic stations. The observed median P-wave relative arrival-time residuals vary between -1.13s (early) in the Alps and 1.12s (late) at the western end of the Carpathians; S-wave relative arrival-time residuals are about twice as large (-2.13s and 3.39s). We tested the effect of deterministic corrections on our relative arrival-time residuals using crustal velocity models from controlled source experiments, but show that the use of station terms in the inversion provides a robust method of correcting for near-surface crustal variation. Our tomographic models reduce the P-wave rms residual by 71 per cent to 0.130s and our S-wave rms residual by 59 per cent to 0.624s. At shallow sublithospheric depths we image several localized lower velocity regions, correlated with higher heat flow and interpreted as upwelling asthenosphere. We image a high velocity structure down to depths of about 350km beneath the Eastern Alps. Further east, beneath the Pannonian Basin, a deeper continuation of the Eastern Alps fast anomaly is imaged trending E-W from ∼300km depth and extending into the mantle transition zone (MTZ). In the MTZ we image a fast anomaly extending outwards as far as the Carpathians, the Dinarides and the Eastern Alps. This higher velocity mantle material is interpreted as being produced by a mantle downwelling, whose detachment from the lithosphere above may have triggered the extension of the Pannonian Basin. © 2011 The Authors. Geophysical Journal International © 2011 RAS. Source


Ren Y.,University of Leeds | Stuart G.W.,University of Leeds | Houseman G.A.,University of Leeds | Dando B.,RockTalk Imaging Ltd. | And 4 more authors.
Earth and Planetary Science Letters | Year: 2012

The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence, extension and convective overturn in the upper mantle. Here, we present high-resolution images of upper mantle structure beneath the region from P-wave finite-frequency teleseismic tomography to help constrain such geodynamical interactions. 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 54 temporary stations deployed by the South Carpathian Project (2009-2011), 56 temporary stations deployed by the Carpathian Basins Project (2005-2007), and 131 national network broadband stations. The P-wave relative arrival times are measured in two frequency bands (0.5-2.0. Hz and 0.1-0.5. Hz), and are inverted for Vp perturbation 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. We suggest that cold mantle lithospheric downwelling occurred below the Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone of SE Romania, intermediate-depth (75-180. km) seismicity occurs at the NE end of an upper mantle high velocity structure that extends SW under the Moesian Platform, oblique to the southern edge of the South Carpathians. At greater depths (180-400. km), a sub-circular high velocity anomaly is found directly beneath the seismicity. This sub-vertical high-velocity body is bounded by slow anomalies to the NW and SE, which extend down to the top of the MTZ. No clear evidence of a residual slab is observed above the MTZ beneath the Eastern Carpathians. These observations suggest that intermediate-depth seismicity in Vrancea Zone is unlikely to be due to slab tearing, but rather could be explained by either gravitational instability or delamination of mantle lithosphere. © 2012 Elsevier B.V. Source


Markusic S.,University of Zagreb | Gulerce Z.,Middle East Technical University | Kuka N.,Polytechnic University of Tirana | Duni L.,Polytechnic University of Tirana | And 8 more authors.
Bulletin of Earthquake Engineering | Year: 2016

The Harmonization of Seismic Hazard Maps in the Western Balkan Countries Project (BSHAP) was funded for 7 years by NATO-Science for Peace Program to support the preparation of new seismic hazard maps of the Western Balkan Region using modern scientific tools. One of the most important outputs of the BSHAP is an updated and unified BSHAP earthquake catalogue that is compiled directly from the datasets of earthquake data providers of the region. The BSHAP earthquake catalogue described here covers the geographic area limited by 38.0°–47.5°N, 12.5°–24.5°E and includes 26,118 earthquakes that occurred in the region between 510 BC and 2012. Details of data compilation efforts including the removal of duplicate events, unification of the magnitude scales, declustering of the catalogue and completeness analysis are presented in this manuscript. New magnitude conversion equations for various local magnitude scales of the data providers are developed with the aim of having homogeneous moment magnitude estimates. Completeness time intervals for the catalogue data are provided as inputs to the seismic source models used to obtain updated seismic hazard of Western Balkan Region. The unified and updated BSHAP catalogue is found to be compatible with the current well-established European and world-wide catalogues and represents a sound basis for analysis of the seismicity of this region. © 2015, Springer Science+Business Media Dordrecht. Source


Mladenovic A.,University of Belgrade | Trivic B.,University of Belgrade | Antic M.,University of Basel | Cvetkovic V.,University of Belgrade | And 3 more authors.
Geologica Carpathica | Year: 2014

In this study we performed a calculation of the tectonic stress tensor based on fault slip data and all available focal mechanisms in order to determine the principal stress axes and the recent tectonic regime of the westernmost unit of the Getic nappe system (Gornjak-Ravanica Zone, Eastern Serbia). The study is based on a combined dataset involving paleostress analyses, the inversion of focal mechanisms and remote sensing. The results show dominant strike-slip kinematics with the maximal compression axis oriented NNE-SSW. This is compatible with a combined northward motion and counterclockwise rotation of the Adria plate as the controlling factor. However, the local stress field is also shown to be of great importance and is superimposed on the far-field stress. We managed to distinguish three areas with distinct seismic activity. The northern part of the research area is characterized by transtensional tectonics, possibly under the influence of the extension in the areas situated more to the northeast. The central and seismically most active part is dominated by strike-slip tectonics whereas the southern area is slightly transpressional, possibly under the influence of the rigid Moesian Platform situated to the east of the research area. The dominant active fault systems are oriented N-S (to NE-SW) and NW-SE and they occur as structures of either regional or local significance. Regional structures are active in the northern and central part of the study area, while the active fault systems in the southern part are marked as locally important. This study suggests that seismicity of this area is controlled by the release of accumulated stress at local accommodation zones which are favourably oriented in respect to the active regional stress field. Source


Kronrod T.,Russian Academy of Sciences | Radulian M.,National Institute for Earth Physics | Panza G.,University of Trieste | Panza G.,Abdus Salam International Center For Theoretical Physics | And 6 more authors.
Tectonophysics | Year: 2013

A unique macroseismic data set for the strongest earthquakes occurring since 1940 in the Vrancea region is constructed by a thorough review of all available sources. Inconsistencies and errors in the reported data and in their use are also analysed. The final data set, which is free from inconsistencies, including those at the political borders, contains 9822 observations for the strong intermediate-depth earthquakes: 1940, Mw=7.7; 1977, Mw=7.4; 1986, Mw=7.1; 1990, May 30, Mw=6.9; 1990, May 31, Mw=6.4; and 2004, Mw=6.0. This data set is available electronically as Supplementary data to the present paper.From the discrete macroseismic data, the continuous macroseismic field is generated using the methodology developed by Molchan et al. (2002). The procedure, along with the unconventional (smoothing method) modified polynomial filtering (MPF), uses the diffuse boundary (DB) method, which visualises the uncertainty in the isoseismal boundaries. The comparison of DBs with previous isoseismal maps supplies a good evaluation criterion of the reliability of earlier published maps. The produced isoseismals can be used not only for the formal comparison of the observed and theoretical isoseismals, but also for the retrieval of source properties and the assessment of local responses (Molchan et al., 2011). © 2013 Elsevier B.V. Source

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