Estimation of Ground Motions in the Valley of Mexico from Normal-Faulting,Intermediate-Depth Earthquakes in the Subducted Cocos Plate

The Valley of Mexico is exposed to seismic risk from normal-faulting, large intermediate-depth earthquakes. We explore two approaches to estimate future ground motions from such events at CU, a hill-zone site in the valley. In the first we obtain parameters of an ω² seismic source model and determine amplification of seismic waves due to local site effects at CU. This permits estimation of Fourier spectrum of expected ground motion at CU from postulated earthquakes. We find that the S-waves suffer an amplification of 2.5 between 0.2 to 3.0 Hz. This amplification is similar to that observed from deep teleseismic events but differs from that obtained from shallow coastal events. In the second approach the available recordings at CU are used as empirical Green's functions (EGF) to synthesize motions from future large earthquakes. This approach is very powerful if the smaller event is truly an empirical Green's function for the postulated earthquake.