engleski

ALPASS-DIPS seismic experiment — Receiver functions analysis on the Alp07 profile

ALPASS-DIPS (Alpine Lithosphere and Upper Mantle PASsive Seismic Monitoring - DInarides-Pannonian Segment) is a passive seismic monitoring project located at the contact of the Dinarides and south-western part of the Pannonian basin. The project is continuation of the successful active source seismic experiment ALP 2002. The major goal of the project ALPASS-DIPS is to apply passive seismic methodology in research of the lithospheric processes and structures related to the transition area between Dinarides and the Pannonian basin. Despite many geological and geophysical studies in this area, tectonic and structural relations have not yet been fully explained. Therefore, this study is yet another attempt to offer a contribution toward a better understanding of the lithospheric and upper mantle structure in this area. To reach this goal, P receiver functions are computed from teleseismic events recorded by temporary seismic stations. Most of the stations (12) were deployed along the profile Alp07 (seismic line from the ALP 2002 project) stretching from Istra, over the islands Cres and Krk, passing near Karlovac and Zagreb to the border with Hungary. The geophysical model of the crust beneath the Alp07 line is already constructed and the deployment within passive seismic experiment along profile Alp07 provides the opportunity to compare the results of the natural and controlled source experiment. Two more temporary stations were deployed in Istra, to the Slovenian border, and one in the Pannonian part, near Slatina. The earthquake recording stations consisted of three-component, shortperiod sensors and data were collected during the period of 18 months. From seismic recordings events with epicentral distances between 30° and 90° were selected and they are mainly with NE and SE backazimuth. The teleseismic P receiver functions are calculated from Ps waves i.e. converted P to S wave at the velocity discontinuities. First, receiver functions are computed for individual temporary stations and later stacked along Alp07 profile to obtain 2-D lateral variation of major velocity interfaces in the crust and upper mantle. The velocity model of the crust and crustal thickness are taken from the results of the active source experiment. The Moho depth obtained from receiver functions analysis generally agree well with results of the active source experiment. From both data sets, crustal thickness is the greatest under the Dinarides, and the thinnest in the Pannonian basin area. Exceptions are two stations located in the transition zone between the Dinarides and the Pannonian basin where agreement is less. This could also be the evidence that transition zone is heterogeneous, characterised by complex tectonics and strong lateral and vertical changes in velocities. Those stations will need to be analysed in more details.

Passive seismic; receiver functions

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