3D numerical modeling of ground motion in the Valley of Mexico: a case study from the Mw3.2 earthquake of July 17, 2019

90/2021

3D numerical modeling of ground motion in the Valley of Mexico: a case study from the Mw3.2 earthquake of July 17, 2019

Thursday 16th December 2021

Hernandez, V.M.; Paolucci, R.; Mazzieri, I.

In this study a 3D physics-based numerical approach, based on the spectral element numerical code SPEED (http://speed.mox.polimi.it), is used to simulate seismic wave propagation due to a local earthquake in the Mexico City basin. The availability of detailed geological, geophysical, geotechnical, and seismological data allowed for the creation of a large-scale (60 km x 60 km) heterogeneous 3D numerical model of the Mexico City area, dimensioned to accurately propagate frequencies up to 1.3 Hz. Results of numerical simulations are validated against the ground motion recordings of the July 17, 2019, Mw3.2 earthquake, which produced peak ground acceleration (PGA) exceeding 0.3g about 1 km away of the epicenter. Results show that for the hill and transition zones of the Valley of Mexico there is a good agreement with records. For the lake zone, the simulated decay trend of the PGV with epicentral distance was reasonably close to the observations, both for the horizontal and vertical components, but synthetics present in general shorter duration with respect to records, probably due to insufficient accuracy of considered values of the quality factor. In spite of these limitations, the simulations proved to be suitable to provide a comprehensive picture of seismic wave propagation in the lake zone of Mexico City, including the onset of long-duration quasi-monochromatic ground motion with strong amplification between 0.5 and 0.6 Hz. The numerical results also suggest that higher-mode surface waves dominate the wavefield in the lake zone of Mexico City, as evident from the measured phase velocities and vertical displacements along vertical arrays. Based on these positive outcomes, we conclude that this numerical model may be used for the simulation of ground motions during larger magnitude earthquakes, for example in view of generation of seismic damage scenarios in Mexico City.

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Geophysical Journal International