MULTILEVEL PROBABILISTIC RISK ASSESSMENT OF SEISMIC LIQUEFACTION ON URBAN SYSTEMS

Apart from extreme cases like the flow-failure example that occurred in 1964 in Alaska (which caused 32 casualties), liquefaction phenomena rarely produce the dramatic and shocking number of casualties typical of other earthquake effects like building collapse, landslides, and tsunamis. The liquefaction-induced impact more frequently regards the foundation of buildings and infrastructures affecting their performance and being responsible for approximately 50% of the total Earthquake-induced economic loss. Several worldwide earthquakes (Turkey, Greece, Taiwan, India, Japan, New Zealand, Italy) have highlighted the complex behaviour of the structure-foundation system subjected to earthquake vibrations. Other effects can be seen on horizontal infrastructures like breakage or disconnection of pipelines or uplift of sewer manholes. These examples highlight the importance of understanding the mechanism triggering liquefaction, predicting soil response subjected to ground shaking and the interaction with the overlying or embedded structures, and transferring this knowledge into robust operative procedures for risk assessment. Since methodologies and approaches of assessing liquefaction potential are the subjects of significant and ongoing research, this document tries to summarize part of the extensive body of technical literature in this area to define a methodology for risk assessment. Considering the variability of possible situations, given by different scopes of the analysis (e.g., loss estimates, urban planning, emergency management, Etc.), different typology of the system exposed (building assets, horizontal infrastructures etc.), different extension (region, municipality, district or even single building) the methodology has been purposely defined in the general terms, leaving a variety of options. Besides, the extensive physical damage produced on buildings and lifelines is only a part of the impact of liquefaction, as injuries are aggravated by the prolonged reduced serviceability of the critical infrastructures, i.e. those systems and organizations that deliver goods and services fundamental for the functioning of society and economy.