In the period of April 24th to 27th, 2023, the field team of Component 2 of the CRONOS project (Stanko, Mravlja and Korbar) performed a field prospection for the installation of the borehole accelerographs as part of the CRONOS project at the Imotski-Opačac location and on the way back on 27.4. in the city of Sinj. In order to define the most favourable location for installing well accelerographs, it is necessary to make a geophysical (including microseismic) and geological prospecting. An important aspect of the geophysical measurements is the correlation with the local geological site conditions, and the field geological interpretation was made by the collaborator on the project, PhD Tvrtko Korbar from the Croatian Geological Institute (HGI). Classic geophysical and microseismic measurements were performed by Asst. PhD Davor Stanko and Bruno Mravlja. The measurements were performed with geophysical equipment Sara Doremi (wired system) and the newly acquired wireless geophysical system Geometrics Atom 1C and 3C (financed with CRONOS project funds), with additional measurement of microseisms using the HVSR method with Tromino devices (financed with CRONOS project funds). The main goal of the measurements was to estimate the bedrock depth, which was estimated to be 35-40 m. Also, for the purpose of further planning of the local site conditions investigation, a wider geological prospecting around the Imotski field was done.
Additionally, the goal of the field research was to collect geophysical measurement data with a wired system and the newly acquired wireless system, for the purpose of testing the new equipment and correlating the results of the two systems. The new wireless system has advantages over the wired system in terms of profile length (not limited by the cable length) and the possibility of passive measurement (and thus significantly greater measurement depths). But, on the other hand, it is not possible to monitor the seismic waves in real-time, which is a significant drawback in active seismic research.
Prepared by Bruno Mravlja