International Conference on Earthquake Engineering and Post Disastor Reconstruction Planning 24 – 26 April, 2016, Bhaktapur, Nepal

Abstract

A method for spectral analysis of the horizontal displacements of the motion due to the propagation of a wave field in an instrumented region is presented. It is considered that the recorded motion is a homogeneous random field whose spectral representation, as in steady state process, consists in the superposition of propagated waves. The power density of the frequency-wavenumber spectrum provides the quadratic mean value of the amplitude of these waves, as well as their velocity and direction of propagation. A kinematic decomposition in terms of waves that produce displacements in the direction of propagation (longitudinal components) and in the perpendicular direction (transversal components) is formulated. The frequency–wavenumber spectral power density is estimated for each component. The analysis of these spectra allows to recognize that the longitudinal and transverse components are result of the superposition of several waves. The interest is to identify the most significant terms of these components and to provide their amplitudes, velocities and directions of propagation. These values, as functions of frequency, constitute the kinematic spectra of the wave field. Results obtained by this method will be applied to confirm or to reinterpret the hypothesis of ground motion Mexico's valley, formulated by others authors. Time history of an earthquake recorded by the Accelerometric Mexico's City Network was analysed in this work. Data were fixed including a common time reference. It is a subduction earthquake with Ms=6.9 magnitude occurred at Guerrero coast on April 25th, 1989.