Recent Tectonic Activity in the Imotsko Polje Area

Displacements of the Adriatic microplate, particularly of its southern part, are of crucial importance for the understanding of recent tectonic movements. Deformations of the structural fabric and the resulting tectonic activity also encompass the studied area. There are four most active fault zones - Mosor-Biokovo, Zagvozd-Vrgorac-Metkovic, Trilj-Tihaljina-Capljina and Imotski-Medjugorje-Popovo polje. In the explored area, these zones delimit the Imotsko polje. The calculated regional stress is oriented in the range between 10-190° and 350-170°. The relationship between the orientation of structural units and stress enables reverse displacements, most frequently in the direction of the south and south-east. The change in stress orientation in the Mt. Biokovo hinterland makes the aforementioned fault zones surrounding the Imotsko polje favourably oriented in respect to the stress, thus enabling dextral horizontal tectonic transport of the structures in different fault blocks. In the two fault zones - Trilj-Tihaljina-Capljina and Imotski-Medjugorje-Popovo polje, there are 98 outcrops suitable for the structural geology measurements. The obtained data on the local stress orientation and spatial displacement of structures are the most important. The character of faults and the most active fault sections are marked, as well as the local structures that are formed due to strong horizontal component of structural displacement in the studied fault zones. Recent tectonic activity is confirmed by the occurrence of earthquakes. Spatial distribution of the earthquake epicentres depicts zones of seismotectonic activity that are related to the aforementioned most important fault zones. Two of the fault zones - Trilj-Tihaljina-Capljina and Imotski-Medjugorje-Popovo polje are especially well marked by earthquakes occurring at depths of between 3 and 15 km