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Rapid changes in geotechnical and geological ground conditions lead to significant ground motion variability. This condition mainly occurs at the so-called basin edges, where there is an abrupt transition between soft highly compressible soils and stiffer materials. This problem becomes more relevant in areas where ground subsidence drastically changes the dynamic response of high plasticity clay deposits, such as those found in Mexico City, due to fundamental site period evolution with time. This paper presents site response analyses at an abrupt transition area in the southeast Mexico City region, along the edges of the Xochimilco-Chalco lakes. Considerable damage associated with three-dimensional wave propagation effects was observed in this zone during the September 2017 Puebla-Mexico earthquake. A series of three-dimensional finite difference numerical models of the basin edge were developed to evaluate ground motion variability, considering topographic effects and soil non-linearities. Good agreement between the computed response and the observed damage during the 2017 Puebla-Mexico earthquake reconnaissance was found. In addition, several normal and subduction events with a return period of 250 years were considered to evaluate the effect that frequency content, and strong ground motion duration have on the soil response variability. From the results gathered here, it was established the relevance of accounting for three-dimensional wave propagation fields to assess site effects at basin-edge zones properly and to be able to implement proper risk mitigation measurements at these zones. [ABSTRACT FROM AUTHOR]

This paper addresses the importance of engineering asset management decisions and control. For this purpose, a Life-Cycle Cost (LCC) analysis is conducted for typical reinforced concrete (R/C) buildings located in Mexico City. The objective of this study is to develop an artificial neural network (ANN) model that can estimate the total expected cost of R/C buildings by using LCC functions. The total cost includes the initial cost and the cost of the damage caused by future possible ground motions at the site of interest. The present value of the cost includes: initial cost, repair or reconstruction cost, cost of damage to the contents, costs associated with the loss of life or injuries and economic losses. The structural performance is evaluated using probabilistic models, artificial neural networks models are used to obtain the seismic response of the buildings. The methodology is applied to a set of reinforced concrete buildings with 4, 8, and 12 stories which are located at the soft soil of Mexico City. Finally, it is concluded that the life-cycle cost is efficiently obtained using artificial neural network models for estimating the structural reliability of reinforced concrete buildings, in such a way that it can be used as an excellent planning tool that covers long spans of time. [ABSTRACT FROM AUTHOR]

The Mexico City basin is an extreme example of an alluvial geological structure that induces long duration and large amplification on ground motions. Researchers have established that the seismic wavefield within the Mexico City basin is composed primarily of surface waves. In the present work, we present a quantitative analysis of the surface‐wave field propagating in the Mexico City basin and generated by thrust‐ and normal‐faulting events. Surface waves are identified and extracted from three‐component ground motion recordings using a technique that exploits the polarization of ground motion. The spatial analysis of the extracted waves clearly shows that the basin response, is strongly dominated by low‐frequency (∼0.25Hz${\sim} 0.25{\rm{\ Hz}}$ to ∼0.5Hz$\sim 0.5{\rm{\ Hz}}$) Love waves. For all seismic events considered, we found that the identified Love waves can reach amplitudes three times larger as compared to Rayleigh waves. Our analysis indicates that surface wave amplification (as defined in the present work) increases with the 1D fundamental resonant site‐periodT1, and appears to be independent of earthquake magnitude. We also quantify the mean delay timetdr${t}_{dr}$ of the central frequencyf0 of the extracted waves. We found that the tdr${t}_{dr}$ of Love waves is spatially more coherent as compared to that of Rayleigh waves. The parameter T1 appears to be a good "proxy" of surface wave effects. This is manifested by a reciprocal relation that was established between T1 and the frequency f0 of the extracted Love waves. Equally important, the latter reciprocal relation turns out to be independent of earthquake magnitude. [ABSTRACT FROM AUTHOR]

Following the 1923 Kanto earthquake in Japan, Japanese researchers noticed the strong effects of surface geology on seismic motion (ESG) and began to investigate these effects to quantify the site amplification factors (SAFs) associated with soft surface sediments. On the other side of the Pacific Ocean, ESG received limited attention until the 1985 Michoacan, Mexico earthquake revealed significant long-period amplification inside Mexico City that manifested as the source of devastating damage to high-rise buildings. Since then, seismologists and earthquake engineers have performed a lot of studies on various ESG issues worldwide. We have not yet reached common conclusions on how to quantitatively predict SAFs over a broad frequency band of engineering interest, 0.1 to 20 Hz, for moderate to strong input from different types of earthquakes in different tectonic settings. However, we found here several basic guidelines useful for successfully modeling ground motions as a common approach to ESG studies. First, in this letter, we briefly review our history of understanding ESG, which is closely related to the key settings required for reliable quantifications of SAFs, and then introduce various emerging techniques for broadband quantitative evaluations of SAFs based on the vast amount of observed ground motions primarily from dense Japanese strong-motion networks. Based on the findings of our investigation and the physical relationships behind the parameters, the authors would like to recommend that researchers on ESG and related topics would refer to the five basic guidelines proposed in the conclusions for the successful implementation of techniques to delineate SAFs in a specific region of interest, such as the use of Fourier spectra instead of response spectra. We have started applying the proposed techniques to regions outside Japan. The implementation of the statistical validation exercises will follow. [ABSTRACT FROM AUTHOR]

In this paper, the authors discuss the extensive structural pounding observed in Mexico City during the September 19, 2017 earthquake. A critical review of the recommendations available for required separations between adjacent buildings in the seismic codes of Mexico City since 1966 is offered. The reasons why these recommendations have not been effectively enforced since then are also addressed. A parametric study was conducted to understand better the structural pounding phenomena for strong ground motions which have been recorded in soft soils in Mexico City during the 1985 and 2017 earthquakes. For this purpose, equivalent frame models for existing reinforced concrete and structural steel flatslab buildings with nonlinear pounding contacts were used. Some well-known proposed equations for building separations were evaluated based upon the results of these parametric studies for pounding. The evaluated equations were the ABS, SRSS and DDC rules, as well as the absolute difference combination (ADC) rule proposed by the authors. From the obtained results, it was found that the minimum building separation between adjacent buildings established in the seismic code of Mexico City should be raised to avoid strong pounding on soft soils. Also, it was found that both the DDC and ADC rules are promising in defining building separations closer to the one obtained from dynamic simulations. These equations are less conservative than the version of the absolute sum rule currently established in Mexican seismic codes. • 98.9% of the observed pounding in Mexico City occurred in the soft soils gained to the former lakes. • The height difference between adjacent structures where more pounding was observed was ±4 stories. • Gap distances required to avoid pounding in the soft soils of Mexico City could be as large as 170 cm. • The minimum distance between adjacent structures to enforce for the soft soils of Mexico City should be raised to 15 cm. • The DDC and the ADC rules could be used with confidence to assess gap distances to avoid pounding in soft soils. [ABSTRACT FROM AUTHOR]