Carpathian Basins Project: 2005-2008

The UK Natural Environment Research Council (NERC) announced on June 22, 2005 that it would fund a major research project whose theme is to understand the role of extension and convergence in the Carpathian Pannonian system of Central Europe.  Principal Investigators on this project are Prof Greg Houseman and Dr Graham Stuart of the University of Leeds. The project is proceeding in close cooperation with Endre Hegedűs, Research Director of the Eötvös Loránd Geophysical Institute of Budapest, Prof. Ewald Brückl of the Vienna University of Technology and Slavica Radovanovic, the director of the Seismological Survey of Serbia.  Major equipment for the project is provided by SEIS-UK, a part of the NERC Geophysical Equipment Facility. Support from the Royal Society has enabled further development of the project in conjunction with the Geophysics group of Prof Frank Horváth at Eötvös Loránd University in Budapest.

Project Summary

The Pannonian Basin was formed as a result of extension of the crust and lithosphere between about 20 and 15 million years ago. To understand why this occurred, and what is the present day structure in the outer few hundred km of the Earth beneath this basin, we plan to: (A) run experiments on computer models that simulate the stress and strain-rate fields and deformation processes on geological timescales, and (B) make seismological measurements of the lithosphere and upper mantle in its present state. We will integrate the results of numerical modelling using a new 3D computer model of gravitational instability in the Earth's crust and lithosphere, and new seismological measurements from a temporary array deployed in Hungary and Austria, in order to develop new and quantitative dynamical models of the extensional process.

Seismic Array Deployment

As part of this study, two new temporary seismic arrays are being deployed in Austria and Hungary during the period 2005-2007.

Regional Broadband (RBB) Array

Alongside existing permanent stations run by national authorities (Yellow triangles on the map), a 10-station Regional Broadband (CBP-RBB) Array using Guralp CMG3T sensors (broadband to 100 sec) was deployed starting in September 2005 (Black triangles) with 8 stations across Hungary, one in Croatia and one in Serbia (in cooperation with the Seismological Survey of Serbia). We plan for continuous recording for approximately 2 years at 100 samples per second.  This array will provide broadband data for determination of structure of the crust and lithosphere by measuring surface wave propagation across the basin, receiver functions, and measurement of anisotropy from shear wave splitting.

High-resolution Seismic Tomography (HST) Array

Starting in April 2006 we have deployed an array for high-resolution seismic tomography (CBP-HST, red symbols on map) for approximately one year.  This array of 46 stations using Guralp 6TD triaxial sensors (broadband to 30 seconds) provided by SEIS-UK will provide data to enable a high-resolution seismic tomography investigation of the Vienna and western Pannonian Basins approximately across-strike of major structural features like the Peri-Adriatic line and the mid-Hungarian line. The map shows 15 stations deployed in Austria (in April), 25 in Hungary (in May), and 6 stations in Serbia (in July).

Photographs of the Austrian HST stations can be seen at HSTA. Further photographs of equipment and deployment methods used in Austria are provided here. Photographs of the Hungarian HST stations can be seen at HSTH. Photographs of the Serbian HST stations can be found at HSTS.

Numerical Modelling of Lithospheric Deformation

A new parallelised 3D Finite Deformation program has been developed at Leeds during 2004-2005 by Lykke Gemmer, Greg Houseman and Stuart Borthwick, with the support of the Leverhulme Foundation.  This program (called oregano) is now being used in a program of numerical experiments testing the hypothesis that the development of the Carpathian Basins and surrounding mountain chains has proceeded as a direct consequence of a gravitational instability of the continental mantle lithosphere beneath the Basin.

Research Personnel

Following Dr Gemmer's departure to join Statoil in Norway, Dr Piroska Lorinczi has been appointed as a Research Fellow to work on the geodynamical modelling part of the project. Array operations in Austria are managed by Mr Helmut Hausmann and in Hungary by Mr Attila Kovacs. Mr Ben Dando will commence his PhD studies at Leeds in October 2006, working on the seismological part of the project.

Project Aims

  1. to develop new time-dependent 3D numerical models of the large-scale strain history of the Pannonian Basin region using a dynamically self-consistent finite element model that solves the basic equations of conservation of mass and momentum in a spatially varying viscous creeping flow, driven by boundary and internal buoyancy forces.

  2. to provide controls on these models by improving the resolution of seismic images of the lithosphere and upper mantle, using data obtained from the two seismic arrays described above.

Seismic tomographic images obtained using data from existing regional arrays shows that the upper mantle of the Pannonian Basin has undergone a major disturbance that is either associated with subduction of oceanic lithosphere or gravitational instability of the continental lithosphere. The lithosphere is anomalously hot and thin and the transition zone contains anomalously cold (seismically fast) material, which observations together imply a general overturn of the upper mantle beneath this region.

Seismicity maps show current deep (to about 180 km) seismic activity beneath the Vrancea Zone of the Romanian Carpathians which, in conjunction with the tomographic images, may be interpreted as continuing downwelling of continental mantle lithosphere.

Studies of the thermal and subsidence history of the Pannonian Basin have shown that the continental lithosphere in this region has undergone a period of rapid extension in the Miocene that has resulted in the thinning and heating of the crust and lithosphere. Crustal and lithospheric extension factors are variable but, in general, the extension factors of the lithosphere appear to be greater than those of the crust by a factor of 2 or 3.

The Carpathian Mountain system encloses several inter-related basins of which the Pannonian is the largest. The lithosphere in the Pannonian may be separated into two domains by major ENE trending structural lineations that include the Balaton line and the mid-Hungarian line. To the NW the Vienna Basin is smaller, but clearly related to the development of the Pannonian system. It remains unclear how these structural elements have interacted during the basin-forming extensional event.

Seismic analysis methods based on data from the new CBP arrays will include receiver functions, surface wave analysis, shear wave splitting and tomography using body waves and surface waves. All of these methods will be used in conjunction with the 3D geodynamical modelling, to help understand how these structural elements have interacted during and since the Miocene basin forming event.