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In this paper, the dynamic response of two 21-story buildings was studied to assess the influence of higher modes in their structural performance. While the first building was structured with ductile moment-resisting steel frames and exhibits a global shear-dominated lateral deformation, the second one uses ductile concentrically braced steel frames and has a global bending-type response. Buildings were virtually located in a soft-soil condition of the lake-bed zone in Mexico City. Nonlinear pushover and dynamic analyses were performed through OpenSees on a detailed 3D-model with plasticity spread along the elements. For this purpose, a set of accelerograms recorded during the Mexico Earthquake of September 19, 2017, were selected, and adjusted to represent the actual seismic hazard at the site. A frequency-domain system identification technique was applied to identify the dynamic characteristics of buildings through a moving-window Fourier analysis, that allows for the estimation of the contribution of higher-modes to their overall nonlinear dynamic response. A ratio of the elastic spectral pseudo-accelerations corresponding to the first two vibration modes is proposed to quantitatively anticipate cases and conditions for which the second mode adversely affects the structural performance of upper stories. The discussion includes a comparative study from the lateral global response of the analyzed models. [ABSTRACT FROM AUTHOR]

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]

The representation of earthquakes (and its aftershocks) is a recurring theme in Juan Villoro's writings. This theme is present in his chronicles, novels and essays in which the imminence of the end and the fortuitous gift of momentary survival trigger meditations that intertwine literature, personal memory, collective and community experience, ethics and politics. This paper discusses two of Villoro's books in which earthquakes take centre stage. The first one is 8.8 El miedo en el Espejo (2010), "a fragmented chronicle" written after the author experienced the Chilean earthquake of 2010, which also echoes the Mexican earthquake of 1985. The second book, Horizontal Vertigo: A City Called Mexico (2018), is dedicated to Mexico City and ends with a fragment about the last quake to jolt the capital in 2017 and with a litany, originally published two days after this last (at the time) catastrophe. Metaphoric connections between the seismic events and the literary, the political and the possibilities of life in common are explored throughout the paper. [ABSTRACT FROM AUTHOR]

Earthquake early warning (EEW) is becoming a popular tool for mitigating earthquake‐induced losses. However, the current literature separates EEW technical components and their operational and behavioural implications. This paper investigates how EEW can be integrated into business continuity practices, organisational resilience, and disaster risk reduction (DRR). A mixed methods approach is applied to analyse EEW perceptions in the case‐study context of Mexico City, Mexico, which is characterised by a high level of seismic hazard and social and physical exposure/vulnerability. The dataset includes evidence from 15 semi‐structured interviews with representatives of the public and private sectors, such as governments and enterprises, and 78 valid questionnaires compiled by local organisations, including civil protection and education institutions. The results reveal inconsistencies between technical EEW methodologies and their integration into three core domains of organisational practice: accountability, governance, and jurisdiction; standardisation of plans and procedures; training and education. Finally, open challenges for future research are highlighted. [ABSTRACT FROM AUTHOR]

The goal of this paper is to examine the seismic resilience of existing eccentrically braced frames (EBFs) in Mexico City under intraslab earthquake ground motions. For this purpose, detailed analytical models representative of EBF buildings designed under the 2004 edition of the Mexico City Code seismic criteria were developed as part of this investigation. These analytical models take into account the nonlinear behavior of the shear links including a failure criterion. Results of this investigation revealed that the archetype EBFs exhibit a nonuniform distribution of maximum interstorey drift, IDRmax, and link plastic rotation, γp, along height, which tend to concentrate at the bottom stories. Furthermore, it was found that γp demands computed from nonlinear dynamic time-history analyses are smaller than that estimated from the current code criterium in Mexico City. Relevant statistical results also include the relationship among IDRmax, permanent interstorey drift demand, RIDRmax, and γp. Suitable equations to predict γp and IDRmax demands are proposed based on the empirical trends of the pairs RIDRmax-γp, IDRmax-γp, and IDRmax-RIDRmax. An estimation of the state of damage of the shear links along-height was performed based on the plastic rotation-based damage states introduced in the literature, which allowed suggesting repair measures to build component-based recovery functions. It is shown that eccentric braced frames are a very resilient structural system to be used in a region of high seismicity such as Mexico City, particularly under strong intraslab earthquakes. [ABSTRACT FROM AUTHOR]

Weak first-story buildings are susceptible to experience severe structural damage, and even collapse, during strong earthquakes as was evidenced during the September 19, 2017 (M w = 7.1) intraslab earthquake that hit Mexico City. Such type of buildings are prone to exhibit a negative slope in their capacity curve due to weak first-story mechanism that might lead to dynamic instability during earthquake excitation. Therefore, this paper presents the main results of an investigation focused on evaluating the collapse strength ratios, R c (i.e., the normalized lateral strength ratio in the onset of dynamic instability) of single-degree-of-freedom (SDOF) systems whose force-displacement nonlinear envelope (backbone) behavior is representative of that observed in existing multistory weak first-story buildings. Particularly, their envelope exhibit several levels of negative slope after a post-yield displacement ductility capacity. Median and dispersion of R c ratios were obtained for degrading SDOF systems subjected to a set of 136 earthquake ground motions recorded in soft soil sites of Mexico City from instraslab earthquakes. Results of this investigation showed that R c ratios depend on the normalized period of vibration with respect to the predominant period of the ground motion, T/T g , the displacement ductility capacity, μ c , and the negative slope after peak strength, α c. Additionally, the spectral trend of R c ratios at soft soil sites is different to that reported for firm soil sites. A continuous functional form is introduced to obtain estimates of median R c ratios for the preliminary seismic assessment of weak first-story buildings in this seismic environment. • Dynamic instability in buildings can be evaluated through collapse strength ratios Rc. • Rc ratios follows a different spectral trend for soft soil sites than for firm sites. • Displacement ductility capacity of structures is beneficial to increase Rc. • Robust equation to estimate median Rc is proposed based on statistical results. [ABSTRACT FROM AUTHOR]