## 1 Introduction  
Seismic response spectra and their application to any structure require knowledge of the seismicity at the location, the geological fault types, the path of the measured seismic waves from the focus to the site of interest, and the attenuation of the wave amplitudes through the Earth's crust. The result of the study is the uniform seismic hazard spectra in a rock layer, represented as a graph of accelerations vs. structural periods, related to a specific return period. Spectral accelerations in a rock layer are used to create seismic hazard maps and regionalization of seismic zones, which are the initial inputs required to obtain the elastic seismic spectrum. To consider site effects due to soft soils, the dynamic amplification factors must be analyzed according to the physical characteristics of the soil in the site of interest, taking into account the stiffness difference between the rock and soft soil layers. Many countries have seismic hazard maps incorporated in their building codes, applying the probabilistic approach according to the seismic engineering methods. In addition, these codes allow for the analysis of a specific earthquake with a deterministic approach for special cases, such as earthquakes of very high magnitude applied to structures of high importance. With the seismic hazard maps and the soil mechanics studies at the site of interest available, including the dynamic properties of the soil, an elastic response spectrum can be obtained, showing, as a result, the spectral accelerations for many structural periods. Its application is directly related to the study of buildings' behavior under different seismic loads. Therefore, it is important to define all the parameters to obtain the seismic intensities and propose structural solutions to adequately support these seismic loads. There are several methods of structural analysis and design that are used to evaluate the displacements and stresses in a building under seismic loads where the force and displacement methods are the most common. The force-based method determines the seismic loads and applies them to the structure to obtain the stresses and displacements on each element. On the other hand, the displacement-based method shows results as global displacements in the first step and, thus, obtains the strain and stresses on each individual element. Traditional seismic engineering and performance-based seismic engineering can use any force-based or displacement-based methods, applying the seismic response spectra as an external load input. National and international building codes establish the minimum requirements for earthquake-resistant structures, including the procedures to obtain the elastic response spectrum and the design spectrum, where the latter depends on different reduction factors according to the characteristics of each building. Mexico has the Design Manual for Civil Works, Seismic Design (in Spanish, _Manual de Diseno de Obras Criiles, Diseno por Sismo_), developed by the Comision Federal de Electricidad, or MDOC Sismo CFE 2015 [1]; the USA has the American Society of Civil Engineers/Structural Engineering Institute or ASCE/SEI 7-16 [2]. For international reference, the International Building Code or IBC 2018 [3] is used. There are more local and international codes that have similar methodologies, showing the procedures to obtain the spectral acceleration in rock layers according to the country's seismic hazard maps. This review article will provide an overview of the methods developed by Mexico, the USA, and IBC to obtain the seismic elastic response spectra according to the seismic hazard variables. The process includes the constant acceleration, regional spectra, and site-specific response spectra procedures, considering as inputs the spectral accelerations in rock layers related to a probabilistic approach.