Search

Many studies have found that ground-motion duration has a considerable influence on damage to conventional civil structures. Historically, Mexico City has been severely affected by long-duration distant subduction earthquakes because of the heterogeneous local site conditions underlying the subsoil of the city, which significantly amplify the soil response. Using a reliable database of earthquakes that occurred in the subduction zone of the Pacific Coast of Mexico, recorded in the hill zone of the Valley of Mexico from 1985 to 2020, predictive models are proposed in this study from existing definitions of strong-motion duration. These models were developed using a mixed-effects approach, which is a statistical method that can consider the correlation between data recorded from the same event. Such models have valuable applications in seismic and structural engineering because they can accurately define the dimension and randomness of strong-motion duration.

Earthquake databases are not sufficiently complete, particularly for soft soils. Also, there are few and oversimplified formulations that allow an understanding on the relation that exists between the elastic and inelastic energy demands for this type of soils. A study on energy reduction factors aimed at establishing inelastic input and hysteretic energy spectra for narrow-banded motions is presented. Unlike previous works, in this study elastic input energy spectra are used as input for energy functional forms that allow the formulation of inelastic energy spectra. For this purpose, over 250 seismic records recorded in soft soils are used. The energy reduction factors yield inelastic energy spectra that capture in a reasonable manner the energy content of narrow-banded ground motions, and yield a better characterization of inelastic energy demands.

A new approach is proposed for the probabilistic financial risk assessment of earthquake-induced tsunami. The risk is evaluated in a probabilistic framework for a full set of hazard events including all uncertainties. The hazard is defined as a stochastic and historic set of events, collectively exhaustive and mutually exclusive, that describes the spatial distribution, the annual frequency and the randomness of the hazard intensity. The risk is expressed as losses in different terms: the average annual loss and the loss exceedance curve. These metrics are of particular importance for risk financing schemes and risk transfer instruments. As an illustrative example, this approach is applied to the probabilistic tsunami risk assessment for public schools in southern Mexico.

Current seismic regulations do not assess the seismic performance of structures during a given seismic event, and therefore do not require an estimation of their residual displacement or level of structural damage. Nevertheless, this information is relevant after intense ground motions to assess the possibility of re-occupying a building. This paper develops simple expressions to estimate the maximum displacement demand from the residual displacement of single-degree-of-freedom systems subjected to long-duration narrow-banded ground motions generated in soft soil sites (particularly, those located in Mexico City). To overcome the limited scope of previous studies, more than 35,000 seismic simulations were performed. The influence of the lateral strength of the single-degree-of-freedom systems is considered. A simplified relation between the residual and maximum displacement demands is established.

A direct boundary element method for calculating the three-dimensional scattering of seismic waves from irregular topographies and buried valleys due to incident P-, S- and Rayleigh waves is presented. It has been formulated with isoparametric quadratic boundary elements and the comparison with other results show that the method is accurate and efficient. The study of the behaviour of two types of mountains for different incidences is also shown. For some incidences, factors of vertical amplification can reach up to 20 times the incident motion and factors of horizontal amplification could be as high as four times the free-field motion. The largest amplifications have been found in mountains with vertical walls while mountains with smooth slopes exhibit little amplification with factors smaller than four. Results in the time domain show how the duration of motion could be incremented compared with the free-field motion and illustrate the great amplification of the incident wavelet at some sites of the mountains.

Ordaz, M., Rosenblueth, E. and Reinoso, E., 1993. Future ground motions in Mexico City. In: F. Lund (Editor), New Horizons in Strong Motion: Seismic Studies and Engineering Practice. Tectonophysics, 218: 141-155. Future ground motions at a soft site of the Valley of Mexico are estimated for a postulated M 8.2 earthquake with epicentral distance of 280 km. Three techniques were used: (a) a semi-empirical estimation of Fourier acceleration spectra at a hard (reference) site plus empirical determination of site effects through empirical transfer functions; (b) semi-empirical computation of Fourier spectra at the reference site, with theoretical calculation of site response using one-dimensional horizontal S wave propagation corrected to account for surface waves; (c) use of an M 6.9 recording as the Green’s function of the postulated event. The three techniques use competing approaches, and we illustrate a rational way for combining them to obtain a single estimate that includes information from the three approaches.

A numerical method is used for calculating the two-dimensional scattering of incident SH waves to try to explain some of the amplification patterns observed from recent data of the Mexico City's accelerometric array. The method is briefly presented and its efficiency is tested against analytical and other numerical solutions for canyons and alluvial valleys. Spectral ratios computed for transition and lake-bed zones of the Mexico City valley with respect to the average motion at hill-zone sites are also presented. The one-dimensional model is used to explain the amplifications observed at a site where the valley is relatively shallow, while the two-dimensional approach is employed at another site at the centre of the valley where irregular amplification patterns have been observed. Results in the time domain are also shown.