engleski

Lithospheric structure at the contact of the Dinarides and Pannonian basin obtained from 2‑ D seismic and gravity modelling on the Alp07 profile

ALP 2002 was big international seismic experiment that focused on the lithospheric structure of the Eastern Alps and surrounding area. Profile Alp07 is one of several refraction and wide angle reflection profiles located in the transition from Adriatic microplate, through Dinarides to Pannonian basin. The 300 km long profile Alp07 stretches in Croatia in the WSW– ENE direction from Istra to the Drava river at Hungarian-Croatian border, approximately perpendicular to the direction of the Dinarides and the main faults in the Adriatic region, including a contact between the Dinarides and Pannonian basin. Two-dimensional seismic modelling was done using tomographic inversion and ray tracing technique. The Moho depth is the greatest in the area of the Dinarides, reaching about 40 km. The depth in the Pannonian basin area range from 30 to 20 km, and is the least at the end of the profile. The boundary depth changes rather suddenly, thus making evident the uneven relief. In order to obtain more reliable data on the crustal composition, the 2‑ D gravity modelling was also performed. The layer boundaries were retained from the seismic model as there was no need to change them during modelling, since varying densities in the model produced a good fit to the data. A geological model was constructed based on both geophysical models. Three types of the crust were found along profile: the Dinaridic and the Pannonian crusts that are separated by a relatively wide transition zone. The Dinaridic upper crust is characterised by low seismic velocities and densities, but its lower crust has high velocities and densities. The Pannonian crust can be seen as unique layer characterised by both low seismic velocities and densities. Large lateral and vertical changes in densities and seismic velocities can be found in the transition zone. Troughs in seismic model at the level of Mohorovičić discontinuity are interpreted as major faults in the lithosphere. Three main lithospheric faults were identified: in north-eastern part of the Dinarides, under the Sava depression, and under the Drava depression. The first one may be considered as a result of subduction of the Adriatic microplate under the Pannonian segment. Similar movements are also defined within the transition zone, where the Pannonian segment is gradually rising over on the Adriatic microplate.

2-D seismic modelling; 2-D gravity modelling; Mohorovičić discontinuity

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