Evidence of subsurface liquefied zone geometries along the Kupa River following the 2020 Petrinja earthquake (Croatia)

Abstract

During the Petrinja earthquake sequence in December 2020, numerous liquefied sand ejections came to the surface along the Kupa, Sava and Glina rivers in Quaternary alluvial sediments. In October 2022, we performed field investigation in the epicentral area, involving geotechnical and geophysical techniques, at different sites with sand ejecta or lateral spreading along the Kupa river to specify the geometries of the various subsurface sedimentary layers and in particular the liquefied zones in depth. For all sites, the sandy ejecta most likely originates from sandy point bars buried under silty layers and located preferentially in the convex parts of meanders. This paper presents and discusses models to highlight the different geometries obtained by geophysics or built from geotechnical soundings for one site located on the eastern edge of an abandoned former meander of the Kupa River.