Liquefaction Probability from 7.0+ Mw Earthquakes in the Megacity of Dhaka, Bangladesh

Abstract

This work assesses the liquefaction potential in Dhaka, one of the world's most densely populated cities in a tectonically active region. Bangladesh has a history of significant earthquakes, emphasizing the importance of assessing liquefaction risk, especially in Dhaka. This study examines the liquefaction potential during earthquakes of 7.0 and 7.5 Mw, considering wet and dry seasonal conditions across three distinct geological zones: Zone 1 (Madhupur Terrace), Zone 2 (Marsh and Artificial Fill), and Zone 3 (Holocene Floodplains). Standard Penetration Test data from 26 boreholes representing these geomorphic units were used to calculate liquefaction probabilities using the simplified procedure method. For a 7.0 Mw earthquake in the dry season, liquefaction probabilities are 68% in Zone 1, 80% in Zone 2, and 88% in Zone 3. In the wet season, these increase to 90% for Zone 1 and 100% for Zones 2 and 3. For a 7.5 Mw earthquake, probabilities rise to 79% in Zone 1, 98% in Zone 2, and 90% in Zone 3 during the dry season, reaching 99% for Zone 1 and 100% for the other zones in the wet season, highlighting that higher earthquake magnitudes and elevated groundwater level greatly expand the liquefaction risk. X-ray diffraction analysis shows that Illite, Kaolinite, and Chlorite are the predominant clay minerals, with smectite found in Banani, which may affect liquefaction risk. The Inverse Distance Weighting analysis of the Liquefaction Potential Index shows that Dhaka City’s upazilas, including Uttara, Turag, Pallabi, Darus Salam, Kafrul, Tejgaon, Rampura, Motijheel, and Demra, are found to be more susceptible to severe liquefaction, with the number of people at risk ranging from 3,669,882 under a 7 Mw earthquake in the dry season to 13,901,544 under a 7.5 Mw earthquake in the wet season. These areas are likely to face significant challenges, including extensive damage to buildings and infrastructure, posing severe risks to the safety of residents.