The 2020Mw 6.4 Petrinja earthquake: a dextral event with large coseismic slip highlights a complex fault system in northwestern Croatia

Abstract

SUMMARY On 2020 December 29, the Mw 6.4 Petrinja earthquake hit the Kupa Valley region and set a record for the largest earthquake in northwestern (NW) Croatia. The coseismic surface displacements are well obtained on three pairs of interferometric synthetic aperture radar images from Sentinel-1 satellites. The interferograms exhibit coseismic ground deformation with a maximum line-of-sight displacement of 0.4 m. Based on the coseismic deformation field, we investigate both the fault geometry and the coseismic slip distribution. The results show a dextral event with a peak slip of 3.50 m at a depth of 3.47 km. The shallow depth and unusually large coseismic slip correspond to obvious ground deformation and serious damage in the epicentral zone. The 2020 earthquake highlights an unmapped, steeply dipping strike-slip fault, which possibly enabled a potential ‘curve cut-off’ process on the bending segment of the Pokupsko fault in the context of ∼N–S compression in NW Croatia. The large coseismic slip and high stress drop associated with the Mw 6.4 Petrinja earthquake are likely products of the geometrically complex fault zones and immature seismotectonic environment in NW Croatia.

Rapid Remeasure of Dense Civilian Networks as a Game‐Changer Tool for Surface Deformation Monitoring: The Case Study of the Mw 6.4 2020 Petrinja Earthquake, Croatia

“…The dip (82-90°), strike (130°), and rake (184.6° ± 1.6°) from our preferred and alternative models (Figure 4 and Figure S4 in Supporting Information S1) are close to published focal mechanism solutions (70-89, 128-134, and 167°-180°, respectively, Baize et al (2022)) and consistent with the long-term morphology of the PPKF and surface ruptures mapped on the field (Baize et al, 2022). Our preferred coseismic slip model (Figure 4) also share common characteristics with InSAR-based solutions outlining at shallow depths (<7 km) a highly steeping (76-84°SW) planar rupture, <6 km wide, with peak slip values reaching 3.5 m (Ganas et al, 2021;Xiong et al, 2022). Indeed, the GNSS-based models confirm a shallow rupture (<7 km) with strike-slip amounts of 4.88 ± 0.69 m (∼3.7 m for the preferred smoothed solution) and high dipping angles (82-90°SW).…”

“…The fault is discretized into 2 km wide sub-faults defined by 15 independent nodes along-strike and 8 along-dip. We perform inversions with different dips of the fault ranging from purely vertical to 70°SW, in agreement with the available data (Baize et al, 2022;Xiong et al, 2022). We invert for the rake and slip amplitude at each node using the horizontal components of both continuous GNSS and civilian benchmark displacements.…”

“…Our sensitivity tests also show that both patches are well resolved, allowing for further interpretations. This complexity could result from diverging constraints in the near-field as the GNSS data coverage is denser and more reliable than InSAR data, which show clear decorrelation along-strike (Ganas et al (2021); Xiong et al (2022), and Figure S1 in Supporting Information S1).…”

The December 2020 Magnitude (Mw) 6.4 Petrinja earthquake, Croatia: Seismological aspects, emergency response and impacts

“…The application of the InSAR methods in computing of the line-of-sight displacement and modelling of the fault parameters by uniform slip inversion were performed by Ganas et al (2021) and Xiong et al (2022). The line-of-sight displacement was estimated at approximately 40 cm and inversion indicate a relatively small fault plane surface was activated, about 8 km × 5 km with a large mean slip of about 3 m without reaching the ground surface.…”

The Impact of Earthquakes on Dropout Doline (Cover Collapse Sinkhole) Development: A Case Study from the Environs of Mečenčani and Borojevići (Croatia)

“…Croatian researchers compiled a comprehensive documentation on the effect of the Petrinja earthquakes and also described the dolines that were formed during this time [1,2]. All other investigations are of geomorphological nature [3], those concerned with remediation measures and priorities for immediate action [4], ground displacement using data from orbits of the Sentinel-1 mission action [5,6]; fault geometry and the coseismic slip distribution [7], earthquake and deformations [8,9]. To date, not a single investigation considered the effect of earthquakes on dropout doline development in the environs of Mečenčani and Borojevići such as the shape of the doline, the inclination of the bearing surface and the rate of doline formation.…”