Extended Abstract

Background and Objective:

The metropolis of Tabriz, located on an extensive alluvial plain and adjacent to the active North Tabriz Fault, is characterized by a high level of seismic risk. Rapid urban expansion, population growth, the development of built-up areas within the fault influence zone, land-use changes, and the proliferation of deteriorated urban fabric have substantially increased the city’s vulnerability to earthquake hazards. This study aims to provide a spatial assessment and simulation of potential earthquake-induced damage under a Modified Mercalli Intensity (MMI) VIII scenario. To achieve this objective, a quantitative and reproducible framework based on catastrophe theory and Geographic Information Systems (GIS) was adopted to support the entire analytical workflow from data acquisition to risk-informed decision-making.

Material and Methods:

The research database consisted of the Tabriz Master Plan (2016), topographic and geological maps, an ALOS-PALSAR digital elevation model, and population data. The selected vulnerability indicators were categorized into three principal groups: (1) natural factors, including distance from the fault, lithological characteristics, and slope gradient; (2) structural factors, including building material type, number of stories; and (3) urban planning factors, including population and building density, accessibility to emergency facilities, availability of open spaces, and characteristics of the road network. A total of 13 indicators were integrated into the modeling framework as standardized, dimensionless spatial layers. To reduce subjectivity in indicator weighting and improve model reproducibility, a hybrid catastrophe theory approach incorporating fuzzy membership functions was applied. The appropriate catastrophe function for each subsystem was determined using the Jenks natural breaks classification method, followed by parameter normalization. Finally, the seismic vulnerability index for the MMI VIII earthquake scenario was derived using an empirical formulation and spatially represented through vulnerability zonation mapping.

Results and Discussion:

The findings indicate that seismic vulnerability in Tabriz results from the interaction of three dominant components. First, geological and geomorphological conditions, including the proximity of extensive urban areas to the active North Tabriz Fault and the widespread construction on unconsolidated sediments and alluvial deposits, significantly increase potential damage levels. Second, structural deficiencies in a considerable proportion of buildings, particularly those constructed using traditional systems with inadequate material quality and limited seismic resistance, contribute substantially to vulnerability. Third, inappropriate urban development patterns, including high building and population densities, expansion within fault-proximal areas, insufficient emergency open spaces, and restricted road accessibility, particularly in older urban districts, further intensify seismic risk. The integrated assessment demonstrates that several parts of the city, particularly Zones 4, 8, and 10 as well as the northern and northeastern sectors, are likely to experience severe damage under an MMI VIII earthquake scenario. In these areas, a considerable proportion of buildings are classified within the high-damage category, with some neighborhoods exhibiting estimated damage probabilities ranging from 50% to 100%. Conversely, the central and southwestern parts of the city, characterized by better building conditions and more balanced urban densities, show comparatively lower levels of vulnerability. Overall, high-vulnerability zones encompass approximately 14% of the metropolitan area, while medium-to-high vulnerability classes comprise a substantial proportion of the city, highlighting the urgent need for targeted risk-reduction strategies.

Conclusion:

This study provides an integrated assessment of seismic vulnerability in the Tabriz metropolis and demonstrates that the city faces a substantial risk of widespread damage in the event of a major earthquake. The combined effects of proximity to the active North Tabriz Fault, deteriorated urban fabric, low-quality construction materials, high building and population densities, and limitations in emergency infrastructure place substantial portions of the city at considerable risk of severe damage under a Modified Mercalli Intensity (MMI) VIII earthquake scenario. The results of this study demonstrate that reducing seismic risk in Tabriz requires an integrated and data-driven approach that combines structural retrofitting, regeneration of deteriorated urban fabric, regulation of development in fault-proximal areas, enhancement of emergency response networks, and improvement of construction standards. The proposed model provides an effective decision-support framework for urban planners and disaster management authorities, enabling the optimization of development policies and emergency preparedness plans based on spatial vulnerability zoning.