# Site-Specific Spectra for the City of Mexicali, Mexico, Obtained from April 2010 Earthquake Records
###### Abstract
For instance, Figure 1 shows the epicenters of earthquakes in the Mexicali region and its surroundings since 1976. Figure 1: Epicenters of earthquakes around Mexicali, since 1976, with a magnitude greater or equal to 5 that were recorded in the CICESE Red. Mexicali is an important city in Mexico since it is one of the common ways to travel to the USA. This city is also the capital of the state of Baja California, Mexico, with a population of more than 800,000 inhabitants. Mexicali is located in one of the most active seismic zones in the country, with more than 150 events with magnitudes greater than 5.0 Mw in the last 100 years. The last major earthquake that shook the city and the entire northwest region of the country and the southwest of the United States occurred on 4 April 2010 (7.2 Mw, Figure 2), about 40 km southeast of the city, causing significant damages. In the city alone, at least 103 buildings with structural damage or which had partially collapsed were reported [13; 14]. Among the recommendations made in 2010 by the Earthquake Engineering Research Institute (EERI) in its earthquake report [13] is improving the seismic design of structures, especially for schools and hospitals. Mexico lacks national building regulations. Instead, two seismic design codes are generally used: the complementary technical standards of seismic design for Mexico City [15; 16; 17], which are primarily used in the cities around Mexico City, and the earthquake design for civil works manual of the Federal Electricity Commission (MOC-CFE) [18]. Design spectra established in local building regulations must be as realistic as possible. They are intended to contribute to ensuring the integrity of the structures in the event of a major earthquake. To do so, they must be subject to updates provided by analysis of real data of the site of interest. The seismic elastic response spectrum can be determined using different procedures according to the building code chosen. However, some building codes recognize that the \"site-specific spectra offer accurate and less conservative acceleration values\" [19]. Several countries have issued seismic design regulations based on the response spectrum. For example, Peru [20] and Ecuador [21] have issued official regulations to reduce the  
Figure 2: Location of the seismic stations used in this study. The yellow triangles indicate stations on sediments, and the brown triangles indicate stations on rock. The star represents the epicenter of the 4 April 2010, earthquake (Mw 7.2), and the rectangle represents the city where the environmental vibration measurements and geotechnical survey were conducted. Epicenters of events with magnitudes greater than 5 in the last 100 years are shown in circles. Tectonic faults are indicated in blue. ordinates of the response spectrum through specific parameters that must be considered when designing civil structures. A procedure to verify if a building code is appropriate for modeling the seismic behavior of buildings is to compare the behavior of a structure considering a site-specific spectrum curve versus the behavior of the same structure considering the elastic spectrum curves of the seismic code. This procedure was recently applied using data from the terrible earthquakes in February in Turkey. Notably, in a recent work, the authors compared the behavior of buildings using the elastic spectrum curves in TBEC-2018 and the behavior using a site-specific spectrum curve [22]. According to the results of this work, when they used the site-specific spectrum, they obtained significantly more seismic damage; for instance, the damage could be increased to 43% in the case of the beams [22]. This kind of result confirms the importance of obtaining site-specific spectra. In the present study, we calculated synthetic response spectra at 5% critical damping for the city of Mexicali based on the acceleration records of the April 2010 earthquake.