The potential of high density seismic arrays to elucidate distributed deformation in the Dinarides and Hellenides

The eastern Adriatic margin with the Dinarides and Hellenides orogens is one of the most hazardous areas in Europe from an earthquake hazard perspective in spite of only moderate shortening rates (e.g. less than 0.5 cm/yr across the Dinarides), as exemplified by the recent highly damaging earthquakes in Durrës, Albania (2019, M6.4) and Petrinja, Croatia (2020, M6.4). Deformation is both fairly localised on shallowly NE dipping thrust faults near the coast, and distributed, with a transition to spatially extended extensional deformation in the southern Dinarides and Northern Hellenides. and a complex regime involving strike-slip and obblique mechanisms in the eastern part of the Northern Dinarides. Making sense of this distributed deformation requires highly accurate locations both horizontally and in depth, which can only be achieved with dense seismic observations.

This region is thus being explored with multi-scale dense seismic deployments. On one hand, the multi-national AdriaArray initiative has combined temporary and permanent broadband stations to achieve a nearly-uniform coverage with typical inter-station distances of 30-40 km. In Albania, where the transition of the Dinarides to the Hellenides is occurring, this regional coverage is complemented by a ultra-dense deployment of nearly 400 stations (mostly geophones with a few broadband sensors) with a nominal spacing of 5 km, which was later rearranged into three orogen-perpendicular profiles, and one along-strike profile with 1 km station spacing. Such large numbers of stations require automated processing approaches leveraging recently developed machine learning-based techniques. The presentation will review the tectonic context for these surveys and share some preliminary results from these deployments as well as an earlier more localised deployment in the area of the Durrës earthquake.