Ground response in the September 19th 2017 Mw=7.1 central Mexico earthquake

Mexico City is mostly built on soft, high-plasticity lacustrine clay. The thickness of the clayey layer varies across the city and is one of the main contributors to ground motion amplification. On September 19th 2017 a M-w 7.1 earthquake struck the central part of Mexico killing at least 370 people, injuring about 6,000 people and causing the collapse of at least 44 buildings in Mexico City, with most of the collapsed buildings being in the zone with a medium clay thickness. Ground motion recordings across the city indicated that this zone sustained greater acceleration, indicating local amplification. This paper studies the spatial distribution of maximum spectral acceleration and the period at which they are observed, to analyze ground motion amplification due to soft lacustrine clays. The amplification observed is explained by the combination of frequency content of the motion, motion intensity and fundamental site period.