Abstract Summary
The earthquakes of September 19, 1985 (M=8.1) and 2017 (M=7.1) together have been the most devastating earthquakes and with the highest number of observed losses, this requires a review of the seismic risk. Thus, this study presents a seismic vulnerability and risk assessment of the urban building stock in Mexico City, an expousure model is proposed using data from the city's Housing Cadastre. In the 1985 event, the greatest damage was concentrated in medium-rise concrete buildings (6-12 stories) both those with rigid frames such as those with waffle slabs, most of them located in Lake Zone (Cuauhtémoc Municipality). During the 2017 event, medium-rise buildings with flat waffle slabs, built before 1985 were again damaged. After the 19, September 2017 we elaborated a database with a total of 1093 damaged buildings, 28% of these structures were classified with damage degree from medium to severe (Grade 3, Grade 4 and Grade 5, of EME98 scale), in Cuauhtémoc Municipality was reported the highest number of damaged buildings with 147 structures. The database was subdivided in ten different typologies of building, including number of levels, age, structural system, floor system. To quantify and characterize the typologies of residential buildings, a statistical study of the buildings from the 16 different Municipalities was carried out, subdividing the database according to the different construction periods, location and number of levels of the buildings. A catalog of vulnerabilities is established through the development of fragility functions for the different typical building classes and combining them with analytics models for risk assessment in Mexico City. Thus, the exposure model is based in the public construction statistics obtained from the cadastre, and census information to characterize the building groups. The seismic hazard is the most studied component required to evaluate the seismic risk in Mexico City. However, there are no specific investigations related to spectral attenuation functions that include local effects. Thus, an probabilistic seismic hazard model was implemented which includes the site effects, where six seismic zones were characterized. The differentiation is made between origin of the earthquakes as interplate and intraplate source mechanism. For each zone, regression models were developed in order to establish the attenuation functions, in this way the site effects are directly included. The seismic hazard assessment was carried out using the classical probabilistic method that allowed to estimate hazard curves and Uniform Hazard Spectra (UHS) for different return periods. Earthquake risk assessment is achieved by means of a probabilistic analysis generating exceedance probability curves, and the probability of damage of each typology was estimated for seismic events with return periods of 40, 100, 250, 475, 975 and 2475 years. The study identified the Municipalities that have the most vulnerable buildings according to their height and year of construction, and thus determine rehabilitation plans and emergency programs.
