A first week of field survey after the Petrinja earthquake (Croatia) confirms surface rupturing

On December 29, 2020, an earthquake of magnitude Mw 6.4 shook the region of Petrinja in northern Croatia, 45 km south of Zagreb.

Considering the high magnitude of the earthquake and the potential occurrence of coseismic deformations over large areas, we contacted our Croatian colleagues from the Geological Institute of Croatia (HGI) to participate in the field investigations and establish the first bases for scientific collaboration. After several on-line meetings, the « EU team » planned a first series of field surveys, despite the sanitary crisis and the cold winter, in order to collect the data before their erosion.

The first week of geological surveys, focused on the surface fracture, has just ended. A second will begin and will develop the recognition of the liquefaction features, numerous in this particularly humid zone of the Kupa river catchment, a tributary of the Sava River. French (Lucilla Benedetti, Adrien Moulin, Maxime Henriquet, Stéphane Baize), Italian (Paolo Boncio, Bruno Pace, Francesco Iezzi, Alessio Testa) and Slovenian (Petra Jamšek Rupnik, Matevž Novak, Rok Brajkovič, Jure Atanackov, Bogomir Celarc, Ana Novak) geologists therefore joined the Croatian colleagues in the field (Branko Kordić, Matija Vukovski, Marko Budić, Marko Špelić, Nikola Belić), to complete the mapping of the rupture already largely advanced by the Croatian colleagues alone. This dataset will enrich the existing database of surface ruptures (SURE ; Baize et al., 2019).

The mapping program was regularly coordinated between the various partners who split into several groups every day. This collective work made it possible to confirm the existence of a rupture of moderate dimension for such an earthquake, with a rupture length of several km and maximum offsets of 15-20 cm, to discuss in the field and to think about future joint actions to improve knowledge of the seismogenic potential of the Pokupsko / Petrinja fault and associated structures, which are still largely unknown and which threaten this populated region of the territory. STAY TUNED!