The CRONOS project is aimed primarily at the development of seismological infrastructure and field investigations. In the same time,  geological investigations are highly needed to determine the structural properties of the Earth’s interior, and ultimately for the numerical modeling of the seismic tremor/shaking.

In order to improve knowledge about the 3D structure of the Earth’s crust, the anatomy of fault systems and their seismogenic potential in the area of northern and central Dalmatia, which is one of the most seismically active parts of the Republic of Croatia, during 2022 and 2023 geoscientists from the Institute for Geology and Geological Engineering (Facult of Mining, Geology and Petroleum Engineering) conducted structural-geological investigations at approximately 400 observation points (Figure 1).

Figure 1 Field geological investigations conducted at approximately 400 points during 2022 and 2023.

Field observations were primarily carried out within the Mesozoic-Paleogene Carbonate Complex (MPCC), which forms the basic structural framework of the terrain of northern and central Dalmatia. In the aforementioned rocks in the wider area of Makarska, Imotski and Posušje, structural-geological data were collected. Structural-geological data compraised geometrical properties data of the primary and secondary structures (e.g. fractures, faults and folds), geometric features of the faults and its kinematic indicators. Based on the observed faults type of deformation processes were determined, but also the kinematic propreties of the mapped deformation structures (Figure 2).

Figure 2 An example of the results of field structural-geological investigations on the MPCC outcrops in the wider area of Makarska, Imotski and Posušje.

In addition to the conducted structural-geological investigations, sedimentological-stratigraphic research was also carried out. These investigations entailed the identification of local lithofacies differences and the identification of the spatial extent of the Upper Cretaceous-Paleogene carbonate complex in which alternate  characteristic deep-water slope facies of Tilovica-Kotišina conglomerate and shallow-water rudist limestones (Ćosović et al., 2006; Figure 3). The delineation of the spatial extent of the mentioned lithofacies at observation points in the thrust domains of the coastal fold-thrust system (Figure 1) was carried out with the aim of understanding the paleogeographic relations in the research area, and thus addressing  the questions of relief dynamics and tectonic evolution during and after their formation.

Figure 3 Field sedimentological-stratigraphic research on outcrops of the MPKK formation within the domain of the fold-thrust system in the immediate hinterland of Makarska. The research was conducted to understand the paleogeographic and tectonic relationships that led to the formation of lithofacies differences in Upper Cretaceous and Paleogene rocks, predominantly composed of conglomerates and shallow-water limestones.

Based on all collected data and with the interpretation of seismic reflection profiles and further fieldwork/analysis of structural data, the regional seismotectonic profile CR-1 (NE–SW trending profile, between the island of Hvar to Lake Blidinje in BiH; Figure 1) with a total length of about 82 km will be finished. Here, the principal objectives are to determine regional structural relationships along the profile line as well as the geometric characteristics of the interpreted faults.

The geometric characteristics of the interpreted faults will be used in the calculation of their seismogenic potential according to the method explained in the work of Wells & Coppersmith (1994). Collected results will be used as one of the input parameters in creating a 3D simulation of the earthquake shaking for the area of the northern and central part of Dalmatia amid the occurrence of a potential stronger earthquake in the study area.

References

Ćosović, V., Premec Fuček, V., Gušić, I., Jelaska, V. & Moro, A. (2006): The age of the Tilovica breccia in Central Dalmatia, Croatia. Micropaleontology, 52/3; 281–286.

Wells, D. L. & Coppersmith, K. J. (1994): New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the Seismological Society of America, 84/4, 974–1002.

Prepared by Assoc. prof. Bojan Matoš