Soil liquefaction and subsidence disaster in Iskenderun related to the 6 February 2023 Pazarcik (Mw: 7.7) and 20 February Defne (Mw: 6.4) earthquakes, Turkiye

The Mw 7.7 Pazarcik earthquake on February 06, 2023, struck southern Turkiye, causing typical liquefaction along the shores of Iskenderun Bay. This liquefaction was characterized by lateral spreading, subsidence, and flooding. Subsidence-triggered sand ejecta, water flows, and opening cracks were identified in areas spanning approximately 2 km in length and 300 m in width. Based on coastal references such as lighthouses or harbor platforms, settlements of 0.8 m and lateral spreading of 0.4% were recorded along the coastal zone following the Pazarcik earthquake. According to camera recordings, liquefaction-related water and silty sand outflows occurred 29 min after the earthquake. The largest water outlet observed had dimensions of 2 m in length, 1 m in width, and 0.5 m in depth. Images captured at the moment of liquefaction show water gushing for 2 m. Granulometric analysis of liquefied sand eruptions at 10 locations on the coast of Iskenderun indicated the presence of silty sand (SM). No water entered the settlement area from the sea during or shortly after the earthquake. The waters that flooded the streets of Iskenderun were largely drained or pumped out after remaining for 3 days. The liquefaction of the main soil zone played a crucial role in the collapse or tilting of tall buildings along the shores of Iskenderun.Lateral spreading and collapse on the shores of Iskenderun were further exacerbated by the MW 6.4 magnitude Defne earthquake that occurred 14 days after the initial major earthquake. Field observations made 25 days after the first earthquake revealed a settlement of 1.7 m and approximately 1% lateral spreading in the coastal zone of Iskenderun.