1 Seismic risk and loss estimation for the building stock in Isfahan. Part I: Exposure and Vulnerability Mohsen Kohrangi 1 , Paolo Bazzurro 2 , Dimitrios Vamvatsikos 3 1 RED, Risk Engineering + Development, Pavia (Formerly Research Assistant, Scuola Universitaria Superiore IUSS Pavia, Pavia, Italy); email: mohsen.kohrangi@redrisk,com; ORCID: 0000-0001-9151-0361 2 Professor, IUSS, Pavia, Italy; email: paolo.bazzurro@iusspavia.it; ORICID: 0000-0001-6107-9451 3 Associate Professor, School of Civil Engineering, National Technical University of Athens, Greece; email: divamva@mail.ntua.gr; ORCID: 0000-0002-4016-5040 Abstract This paper focuses on the exposure and fragility/vulnerability of the residential, mixed residential/commercial, and public building stock of the city of Isfahan, in Central Iran, and constitutes the first part of a seismic risk assessment study for that city. To determine the assets at risk, we first summarize the details of the building stock and population from the available georeferenced 2011 Census data. From this dataset and from a local survey of the city, we categorize the building taxonomy in 27 construction classes characterized by age, height, and material/lateral-load-resisting system. A building exposure model is then assembled by first dividing Isfahan in city blocks and then by assigning the appropriate statistical properties to the buildings, such as construction class, built area, and replacement cost. The population of each city block is also estimated and accounted for. To assess the fragility and vulnerability to earthquake ground motion, for each building class we performed nonlinear dynamic analysis of multiple equivalent single-degree-of-freedom systems. This process generated a set of class- and region-specific fragility and vulnerability functions that considered both record-to-record and building-to-building response variability. In the companion paper we used the exposure model and the fragility and vulnerability curves generated for all these asset classes to probabilistically assess the seismic risk of Isfahan. Key words: Urban Risk Assessment, Earthquake, Isfahan, Iran 1. Introduction Iran is located in a seismically active region with a long history of devastating earthquakes. Major recent damaging earthquakes in Iran include M7.3 Kermanshah 2017 with 630 deaths, M6.6 Bam 2003 with 26,271–43,200 deaths, M7.4 Manjil-Rudbar 1990 with 35,000–50,000 deaths, and M7.2 Buin-Zahra 1962 with 12,225 deaths, among others. These seismic events and the large number of fatalities evidently indicate that Iran is one of the most active and vulnerable zones in terms of seismic hazard and risk. The greater Isfahan (32°38′N 51°39′E) is a historical and touristic city in the center of Iran. It has a population of about 1.6 million according to the 2016 Census, the third most populous metropolitan area in Iran after Tehran and Mashhad. According to the seismic zonation of the Iranian seismic design code (ICSRDB 2014), Isfahan is located in a zone of moderate seismic hazard with reference peak ground acceleration, PGA, on rock equal to 0.25g for a 475 year return period. Even though the estimated seismicity of Isfahan is lower than that of other seismically active large cities in Iran (such as Tehran, Tabriz and Mashhad), the large number of vulnerable buildings, the large compact population and the importance of the post-disaster functionality of the city (i.e., resilience) for the economy of the country, call for a thorough pre-disaster seismic risk and loss estimation study. Such studies can play a fundamental role in the sustainable development of the urban area, providing local authorities and other national or local decision makers with valuable information for the identification of appropriate risk mitigation actions. These actions include, for instance, post-disaster emergency planning, devising pre-earthquake building retrofitting campaigns, creating insurance pools, and strategic urban planning,