Liquefaction effects in the 2020 Mw 6.4 Petrinja, Croatia, earthquake

The 2020 M w 6.4 Petrinja, Croatia, earthquake triggered widespread liquefaction along the Kupa, Glina, and Sava rivers. The locations of liquefaction ejecta and lateral spreading were identified through a combination of field reconnaissance and interrogation of aerial photographs. Superimposing those locations on the regional geologic map revealed the liquefaction vulnerability of Holocene terrace and flood deposits, Holocene deluvium-proluvium, and Pleistocene loess deposits. Liquefaction caused damage to the land and structures, with ejecta observed both near and far from residential structures. In the free field, the ejection of silty and sandy soil accompanied the extensive ground fracturing. At residential properties, ejecta led to differential settlement, cracks in foundations, walls, and floors, and contamination of water wells. Lateral spreading resulted in the formation of ground and building cracks, house sliding and tilting, pipe breakage, and pavement damage. This article documents these observations of liquefaction and draws conclusions regarding the patterns of liquefaction observed in this earthquake. These observations will be a valuable addition to liquefaction triggering databases as there are relatively few earthquakes with magnitudes less than 6.5 that triggered extensive liquefaction, and they provide additional case histories of liquefaction in Pleistocene deposits. • Liquefaction effects were observed up to about 20 km from the fault rupture. • Liquefaction ejecta and lateral spreading damaged land and light-weight structures. • Ejecta caused differential settlement of houses and contamination of water wells. • Lateral spreading resulted in house sliding, tilting, and cracking. • Quaternary deposits near active stream channels manifested liquefaction.