HISTORICAL OCCURENCE OF LIQUEFACTION IN ZAGREB AREA AND ESTIMATION OF REOCCURENCE IN CASE OF ANOTHER STRONG EARTHQUAKE

During the Great Zagreb's earthquake in 1880 consequences of the liquefaction have been detected at six sites in the vicinity of Zagreb as the occurrence of sand boils. Liquefaction takes place when loosely packed, water-logged sediments near the ground surface lose their strength in response to strong ground shaking. During the liquefaction, due to pore pressure buildup, water may be forced to the surface carrying sand particles through volcano-like sand boils. Important factor for liquefaction occurrence is the state of soil densification which relates to geological age of deposits. Results of the absolute dating of fossilized trees found in Sava's alluvium in the vicinity of Zagreb and the results of the penetration tests show that another earthquake with magnitude ≥ 6.3 can provoke liquefaction once again.