Insights into Liquefaction-Triggered Lateral Spreading in Brest Pokupski During the 2020 Petrinja Earthquake

This paper presents a numerical analysis of liquefaction-induced lateral spreading at Brest Pokupski in Croatia, observed during the 2020 Mw6.4 Petrinja earthquake. The site is composed of Holocene alluvial deposits consisting of loose to medium-dense sands, silty sands, and sandy silts with high groundwater levels, locally confined by low-permeability cohesive layers, which together created favourable conditions for excess pore pressure generation, liquefaction and lateral spreading. During the 2020 Petrinja earthquake, the area experienced large-scale ground failures, including widespread soil deformations, sand ejecta, ground cracking and settlement, making it one of the most prominent manifestations of earthquake-induced liquefaction in the affected region. The study applies dynamic analyses using the advanced constitutive models and soil parameters derived from laboratory tests and CPT investigations. The model simulates excess pore water pressure development and resulting ground deformations, with displacements evaluated at advanced stages of dissipation. During the dissipation phases, the model exhibits a high sensitivity to hydraulic conductivity, which may be attributed to slight residual numerical imbalances at the end of shaking. Consequently, scaling factors of 100 and 1000 result in horizontal displacements of approximately 20–30 cm and 60–70 cm, respectively, within the liquefiable layer. Trends of ground displacement with distance along the profile, however, remain consistent regardless of the applied scaling factors, and can therefore be used in conjunction with displacement measurements to assess the response. Numerical results are used in conjunction with InSAR observations from the European Ground Motion Service (EGMS) and geodetic benchmark measurements to assess the displacement field changes along the profile. The comparison from two points showed a shift in the displacement direction towards the river by about 14∘.