# Seismic Risk in Alborz: Insights from Geological Moment Rate Estimation and Fault Activity Analysis
## 2 Tectonic Setting and Seismicity  
The Alborz mountain range is an intercontinental fold-thrust belt of about 1000 km in length and a width of about 500 km with an approximate east-west trend within  
Figure 1: Location of the study area: (**a**) Depicts the northern region of Iran and the southern area of the Caspian Sea on a smaller scale, providing a general overview of the study area’s geographic context. (**b**) Illustrates the specific location of the study area in greater detail, showcasing names and positions of cities, along with identification of the main faults. the Alpine-Himalayan orogenic belt (Figure 1). The Alborz, located on the boundary between the Turan-Ural Platform and the Central Iranian Subcontinent, is the northernmost deformation zone resulting from the convergence of the Arabian and Eurasian Plates. The study area is located in the north of Iran and between the latitude of \(\sim\)35\({}^{\circ}\)01\({}^{\prime}\) N-38\({}^{\circ}\)48\({}^{\prime}\) N and the longitude of 56\({}^{\circ}\)59\({}^{\prime}\) E-48\({}^{\circ}\)01\({}^{\prime}\) E (Figure 1). In seismically active regions is always a relationship between the identified active faults and the earthquakes in terms of location and depth. Thus, the study of characteristics of the active faults can be the basis for seismic surveys of a region. In the Alborz region, the active faults, which usually cut the Quaternary units, have been marked on the geological maps (scales; 1:250,000, 1:100,000) and satellite imagery in various international articles [10; 11; 12] (Figure 2). The main active faults of the Alborz with a dominant component of thrust surround the area from the north (e.g., North Alborz, Khazar SSW-dipping faults) to the south (e.g., Garmsar, North Tehran, Jajarn, Pishva N-dipping faults), while the strike-slip movement is concentrated inside the range (e.g., Rudbar, Firuzku, Mosha) [14; 15; 16; 17]. In certain regions of the Earth, significant seismic activity has been observed, including past occurrences of large earthquakes, as documented by [18; 19; 20; 21]. Understanding historical seismic events and their locations is crucial for conducting seismic hazard analysis, as emphasized by [22]. This study has compiled and examined historical earthquake data from various sources, such as books and articles [23; 24]. The seismicity of each structural zone has been studied over two periods: the pre--20 th century (pre-instrumental) period and the instrumental period that followed the development of seismic instruments in the late 19 th century. Figure 3 and Tables 1 and 2 provide information on instrumental and historical earthquakes in the study area. The region has experienced several significant instrumental earthquakes, such as the 1935 Mw 6.8 Kusut, 1953 Mw 6.5 Troud, 1957 Mw 7 Sangchal, 1962 Mw 7.2 Buin-Zahra, 1980 Mw 6.6 Shirabad, 1990 Mw 7.3 Rudbar, 2002 Mw 6.5 Avaj, and 2004 Mw 6.4 Baladeh earthquakes, resulting in considerable economic and human losses, as reported by [23; 25; 26; 27]. The historical sites in the immediate southern foothills of the Central Alborz, particularly around Tehran, have been devastated multiple times by historical earthquakes, as noted by [23; 26]. The Eivanaki, North Tehran, and Rey faults have been identified as sources of historical earthquakes, occurring in 1384 AD, 1177 (Ms 7.2), 855 (Ms 7.1), 743 (Ms 7.2), and 312-280 BC (Ms 7.6), as reported by [23; 26]. Thus, considering the current population of approximately 13 million, Tehran may face significant seismic hazards. Figure 2: Active faults of Alborz in northern Iran [13; 14]. Figure 3: The instrumental earthquake epicenter of the Alborz mountain range and its surrounding areas.