Quantitative Analysis of Surface Wave Propagation from Recorded Seismograms in the Mexico City Valley

Session: Advances in Upper Crustal Geophysical Characterization [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Mexico City valley is a paradigmatic example of an alluvial structure generating large ground motion amplification and energetic low frequency waves. Through observations and numerical simulations researchers have established that the seismic field in the Mexico City valley is mainly composed of surface waves, and the discussion of their role in the duration and intensity of the surface ground motion is ongoing. In this work, we present a quantitative analysis both in space and time of surface waves propagating in the Mexico City valley during six major events with similar epicentral location, including the M7.1 September 19th, 2017 Puebla-Morelos normal earthquake. Rayleigh and Love waves are identified and extracted from three-component recordings using a technique that interprets the polarization characteristics of the waves in terms of orthogonal relations that are quantified by means of inner products. The spatial analysis of the extracted surface waves highlights that the basin response expressed by mean amplitude and mean duration is strongly dominated by low frequency Love waves. We observe that the Love waves with stronger amplitudes emerge in a region previously identified as the deepest part of the basin. Less energetic Rayleigh waves are identified in the basin with stronger amplitudes near the basin edges. We also quantify dispersion characteristics by estimating the mean delay time of the predominant frequency of the extracted waves. We observe significant dispersion for Love and Rayleigh waves, although the spatial distribution of the time delay is more clearly defined in the case of Love waves. We observe that the extracted Love waves increase their duration as they propagate through the valley, however the duration increase with respect to the remaining signal remains below 20 per cent. The duration of the extracted Rayleigh waves does not appear to exceed the duration of the remaining signal. Our preliminary conclusion is that while the Love waves are clearly ‘basin-induced’, the Rayleigh waves appear to be associated with other causative factors.

Presenting Author: Kristel C. Meza-Fajardo

Authors