# Site-Specific Spectra for the City of Mexicali, Mexico, Obtained from April 2010 Earthquake Records
###### Abstract  
The April 2010 earthquake (Mw = 7.2), which occurred about 40 km to the southeast of the city of Mexicali, Mexico, caused significant damage to buildings. To improve knowledge of the seismic response of the soil due to the occurrence of earthquakes, a response spectrum at 5% damping was calculated. A comparison between the spectral ordinates obtained in this study and the spectra proposed by the regulations of the Federal Electricity Commission (CFE for its acronym in Spanish) in its seismic design for civil works manual, which is currently used as the design standard throughout the country, was made. We calculated response spectra using records from the April 2010 earthquake and a stratigraphic profile of the city to calculate a transfer function. We first corrected the records for site effect due to stations being over sedimentary soil, and then used them as Green functions to perform a numerical simulation of propagation through the stratigraphic profile to obtain a simulated surface record from which response spectra were calculated. Additionally, ambient seismic noise was measured at the same site to get the dominant period (_To_). We observed that the transfer function was similar to the spectral quotient up to 5 Hz and that _To_ calculated in both ways gave similar values. The comparison suggests that the design spectrum of the CFE regulation can be considered as a representative spectrum for Mexicali for periods greater than 1.3 s, but not for the zone of short periods. s 2024 14 7586 20  
that we need to increase efforts to improve our ability to support against future earthquakes with significant potentials for seismic damage. Seismic damage in buildings depends on different factors. Still, to simplify the problem, we can mention that seismic damage in a building is mainly a function of the building's vulnerability and the features of the ground motion. Every day, we have more knowledge about building buildings that can withstand or not receive damage during and after a significant earthquake. However, this new knowledge does not resolve the complete earthquake-related problem, because we still have buildings built with old seismic codes. And, because we also have cases where new buildings or houses are being built without using modern seismic codes. Therefore, different governments have made important efforts to contribute to offering economical resources to retrofit buildings with high vulnerability or seismic risk. Concerning the type of seismic damage in buildings in the three cases mentioned previously, it is possible to say that, in general, the damage occurred in buildings with specific vulnerabilities. For instance, the vulnerabilities could be related to some of these conditions: (a) the seismic code used to design the buildings is not recent, (b) the presence of building errors or deficient quality of materials, (c) modification of the original project without appropriate structural analysis, etcetera. Therefore, it is not easy to answer the following question: how can we obtain the economic resources required to retrofit the buildings that we know have significant vulnerability? On the other hand, significant projects have been developed worldwide to understand more about the features of seismic ground motions. If we know, with more certainty, the features of the next earthquakes, then we have a better chance of determining the probable seismic behavior of our buildings and modifying or designing them to withstand those major earthquakes. To understand more about the damage after an earthquake, it has been possible to identify that, in general, the damage distribution due to large seismic events depends on several factors, among which site effects stand out. The impedance contrast between the surface layers and the basement can significantly amplify the waves traveling through the subsurface and lengthen the duration of the ground motion. It is essential to highlight that the city of Mexicali has been affected by significant earthquakes.