Abstract

The Acambay earthquake of 1912 (M∼7.0), which occurred in the central Trans-Mexican Volcanic Belt (CTMVB) about 100 km west–northwest of Mexico City, has been thought to be a critical scenario event in the estimation of seismic hazard of the city. We use seismograms of two small earthquakes located near Actopan (15 December 2003; 18 May 2010) and recorded at station CUIG, a hill-zone site in Mexico City, as empirical Green’s functions (EGFs) for the Acambay region. Because Actopan, like Acambay, is situated in the CTMVB and both are located at about the same distance from CUIG, the use of the recordings of the Actopan earthquakes as EGFs is partly justified. We first analyze data of the two small earthquakes at a local station, DHIG, to estimate their seismic moment and stress drop. As there is considerable uncertainty in the estimated stress drops of the two events, we choose a reasonable range of values for them and apply a technique of random summation of EGFs to simulate ground motion at CUIG from a postulated Mw 7 earthquake. The estimated geometric mean horizontal peak ground acceleration (PGA) and peak ground velocity (PGV) at CUIG range from 2.7 to 9.7 cm/s2 and from 1.1 to 3.0 cm/s, respectively. Ground-motion maps for the entire city are presented using a simulated trace at CUIG and the known transfer functions of many sites within the city. The results are consistent with reported seismic intensities in Mexico City, and PGA and peak ground displacement (PGD) at a 2-s period at the seismic station of Tacubaya during the Acambay earthquake. Estimated ground motions suggest that a repeat of the event does not present significant hazard to Mexico City.

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