ABSTRACT: More than 1100 buildings are part of what today it is known as the world heritage downtown of Morelia city, in Mexico, honor given by the UNESCO since 1991. Unfortunately, in this country many historical buildings are located on a high seismicity zone, as it is the case of Morelia; therefore, it is of importance to lead works with the aim to assess the seismic behavior and the vulnerability of heritage buildings. This is a complex task that involves specific and detailed analytical models for each of the existent buildings, further it have to be considered the seismic zone and the soil type where they are located. A 3D finite element model was built for the XVII century Morelia cathedral considering both bell towers geometry in detail plus the main façade and the first vaulted bay. The analytical model of the building was calibrated using experimental modal properties obtained from ambient vibration measurements; previous steps allowed estimating the average global mechanical properties of the materials. Considering the Drucker2Prager and Smeared Cracking formulations for compression and tensile regimen a set of capacity curves were generated for several control points on the structure through a static nonlinear pushover analysis. The evaluation of the performance points was reached considering the site seismic demand from a probabilistic seismic hazard analysis, given as a result the generation of fragility curves for several limit states. The results showed an acceptable behavior for both bell towers since their evaluation led to a moderate damage level under the earthquakes with return periods of 475 and 975 years. On the other hand for the same seismic demand, it resulted that the north vaulted bay could present a moderate2extensive damage level, showing a high vulnerability level. These results show the need for further research that will consider the rest of the building in order to establish a more reliable damage scenario for this Mexican heritage building. KEY WORDS: Historical buildings; Seismic vulnerability; Seismic hazard; Cathedral; Seismic demand; Pushover analysis; Damage grade; Ambient vibration; Finite element; Fragility curves. 1 INTRODUCTION The Morelia cathedral (Figure 1) is a Baroque style building designed by Vicente Barroso de la Escayola and its construction began around 1660 and it was concluded in 1774. During this period, the works were suspended at different stages. Once completed, the cathedral has undergone significant historical earthquakes such as the one occurred in June 19 th , 1858, which produced high damages in several masonry buildings in the south2central part of the country. Figure 1. Morelia cathedral back view. 2 NUMERICAL MODEL In order to achieve enough precision in the evaluation of the cathedral response, a 389 541 tetrahedral finite element model was generated (Figures 2 and 3), to be the main structural basis for the analysis and evaluation of the seismic vulnerability of the system. The numerical model of the structure corresponded to both towers interacting with the north wall façade and the first vaulted bay plus the chapels adjoining both bell towers. In this research we chose the finite element technique for modeling the cathedral because this methodology reproduces whit an acceptable accuracy the masonry behavior, the model can be calibrated with the properties obtained experimentally and there are several constitutive models to represent the material nonlinearity. Although these models are time consuming, particularly when accounting for the nonlinear response, this is one of the best techniques to reproduce the behavior of heritage buildings. 3 EXPERIMENTAL DINAMIC PROPERTIES AND MODEL UPDATING An experimental layout was carried out in order to obtain the dynamic properties of the structure. This campaign consisted in developing a set of ambient vibration measurement over different points along the structure [13]. Using the well know   technique [4], and assuming a small damping ratio as that the modes are well separated. Several modal          Guillermo Martínez 1 , Rodolfo Gaytán 1 , Rafael Rojas 1 1 Department of Civil Engineering, Universidad Michoacana de San Nicolás de Hidalgo, C. Francisco J. Mujica s/n, Ciudad Universitaria, Morelia, México email: gmruiz@umich.com, gaytan444@hotmail.com, rrojas@umich.mx