On the duration of seismic motion incident onto the Valley of Mexico for subduction zone earthquakes

We have used finite difference simulations in 2-D models of the lithosphere to estimate the duration of long-period (>2 s) ground motion incident onto the Valley of Mexico for subduction zone earthquakes. Our simulations suggest that two heterogeneous structures extend the duration of the ground motion between the subduction zone and Mexico City by more than 1 min: (1) the Mexican Volcanic Belt and (2) two low-velocity layers in the coastal region; the accretionary prism and the water layer. The duration generated by a crustal model including these structures is similar to that for earthquake records observed in between the coast and Mexico City. In the Valley of Mexico, our models including only regional-scale heterogeneity reproduce approximately one half of the observed duration. The results suggest that both the regional- and the local-scale low-velocity structures must be taken into account in order to explain the observed extended signal duration in the Valley of Mexico.