Assessment of liquefaction occurrence conditions in Quaternary marine sands: case study of the November 26, 2019 earthquake in Durrës (Albania)

International audienceThe Albanian earthquake of November 26, 2019 with Mw magnitude of 6.4 caused severe impacts in Durrës city built above a Plio-Quaternary basin. The damaged buildings are the consequences of several factors including strong ground motion, local site amplification, poor building workmanship and soil liquefaction. This last phenomenon occurred along the coastal Durrës bay into Quaternary marine sands (Q4dt). To date, the conditions that triggered ground liquefaction and its consequences remain poorly understood. Using existing site data and post-seismic observations, this study examines the conditions that may have triggered liquefaction along Durrës Bay. The analysis from soils properties reveals different liquefiable sandy and silty soils in the Q4dt formation. The simplified procedure based on geotechnical data indicates that the maximum ground acceleration (PGA) of 0.19g appears to be underestimated. Higher acceleration values could have been achieved due to seismic motion amplification effects associated with a shear wave velocity contrast located at the base of the Q4dt formation. Alternatively, another approach would tend to indicate that a sufficient number of cycles could have induced liquefactions without necessarily a PGA higher than 0.19g. However the latter result is based on the untested assumption that the ground motion recorded at the Durrës station can be transposed along the bay. The hypothesis of an acceleration higher than 0.19g along the Durrës bay remains the most plausible because of different soil conditions compared to the plain. These results also raise the need to pay more attention about the seismic sequence, and, in particular, to the occurrence of strong foreshocks that can alter soil characteristics