SOME PRELIMINARY RESULTS AND ANALYSIS OF DIFFERENT GEODYNAMIC TECHNIQUES WITH SPECIAL REMARK ON GPS AND TILTMETER MEASUREMENTS IN CROATIA

摘要

Croatia lies in a region, which is seismotectonically very active. The main reasons for this are the Adriatic microplate movements towards the Dinarides, with its different specific densities of rock masses in the crust. There are several zones in the Adriatic Sea but also along the Adriatic Coast experiencing in the past heavy earthquakes with damages in cities (Dubrovnik, Makarska, Rijeka, Ston, and Zadar). Also, there are some local zones in the inland regions (Gospic, Knin, Zagreb and others) which are not directly coupled with the above mentioned dynamics. Therefore, several different measuring methods and techniques applied in different zones are used (and others are planned) to determine the changes in position, height, tilting, and gravity, which will enable the creation of better earthquake prevention models. Two main projects for deformation monitoring are still running. The first project is: a) The monitoring of the Adriatic Sea area deformations with a part of the inner land, and the other is b) the local deformation net of the broader area of Zagreb. The monitoring is based on GPS measurements. For the investigation of the present tectonic activities in the Adriatic Sea area, a wider GPS network was established. The network consists of 22 stations that are distributed over Croatia (17), Slovenia (3) and Italy (2). In 1996, the network was extended towards the south and west with 7 stations in Albania (4) and Italy (3). The GPS network has to be remeasured several times and from the repeated data, velocity vectors will be calculated. The results of the deformation analysis, based on the analytical surface deformation theory, indicates three different deformation zones in the investigated area. Tilt measurements in combination with gravity measurements in the future along the coast will have to prove the theory of three separate microplates in the Adriatic basin. To observe earthquake precursors (if they occur), continuously on-line tiltmeter measurements are planned. Since the Geophysical Institute in Zagreb has been recording earthquakes for more than hundred years till now, these data are to be included as well. Also an absolute gravity network with selected measuring points which will cover the main part of Croatia as well as a GPS permanent network is planned in the future. The combination of data from different origin will enable the usage of crust behaviour models in future. Based on such models a better understanding of earthquake origins and prevention, especially around cities could be obtained.