1-Introduction
Tabriz, as one of Iran's major metropolises, is situated adjacent to the large and active Tabriz Fault, which has a significant historical record of seismic activity. Rapid and unplanned urban development, particularly along axes aligned with the fault and construction on unsuitable geological units (such as clay and marl hills east of the city), has dramatically increased the sensitivity and vulnerability of this metropolis to earthquake and landslide hazards. Therefore, the precise identification of active and concealed fault branches and the analysis of related morphotectonic hazards are considered a scientific and essential foundation for risk management planning, hazard mitigation, and achieving urban resilience. The present research, with the primary objective of identifying active branches of buried faults within the Tabriz metropolitan area and conducting a spatial analysis of related hazards, has been carried out by integrating geophysical methods and geological studies.
2-Materials and methods
This research is an applied-developmental study conducted with a descriptive-analytical approach. The study area is the metropolitan city of Tabriz in East Azerbaijan Province. The data used include geological and tectonic information (comprising aerial photographs and field surveys), as well as electrical resistivity geophysical data. The primary method for collecting field data was the electrical resistivity method. In this study, the ARES instrument manufactured by GF Instruments of the Czech Republic was utilized. Data acquisition was performed through two-dimensional profiling using a dipole-dipole electrode system. After acquisition, the raw apparent resistivity data were processed and subjected to two-dimensional inversion using the specialized software Res2Dinv. The output of this stage consisted of two-dimensional cross-sections depicting the distribution of true resistivity along each profile. Finally, for integrated interpretation, these cross-sections were analyzed and visualized alongside information derived from tectonic studies (known fault locations) using Global Mapper and Google Earth software environments.
3-Results and discussion
The results of inverting resistivity data from the six studied profiles provided a clear image of the subsurface structure and evidence of faulting activity:
A. Resistivity Values: The range of resistivity values in the profiles was generally low to moderate (from less than 1 to about 500 ohm-meters). This indicates the deep extension of alluvial deposits (sand, silt, clay) as well as the weathering and fracturing of older rock units at depth. However, at certain specific points, high resistivity values were recorded, attributed to the presence of hard, less-weathered rock units (such as limestone) beneath softer deposits.
B. Identification of Discontinuities and Fault Branches: Clear discontinuities were observed in the resistivity distribution pattern across all studied profiles. These discontinuities, appearing as sharp boundaries between areas of distinctly different resistivity and often in vertical or diagonal orientations, were interpreted as indications of faulting or fractured zones.
C. Discovery of New Discontinuities: In addition to confirming the location of known faults, the resistivity models revealed several other discontinuities along fault trends. These could represent subsidiary branches or small-scale buried faults that had not been previously reported on geological maps.
D. Geological Interpretation: The gradual or abrupt variations in resistivity along the profiles were primarily interpreted as resulting from changes in sediment grain size (transition from fine-grained to coarse-grained sediments or vice versa), variations in moisture content, and the boundary between soft alluvial deposits and the underlying hard bedrock.

4- Conclusion
This research clearly demonstrated the effectiveness of the electrical resistivity method using a dipole-dipole system and processing with Res2Dinv software in identifying and tracing active branches of buried faults in the urban environment of Tabriz. The key findings of the study are as follows:
A. The subsurface structure of the area predominantly consists of low-resistivity alluvial deposits, which makes the precise detection of fault discontinuities challenging; however, with adequate data coverage and accurate processing, this was successfully achieved.
B. The location of many discontinuities identified in the resistivity data corresponds to known faults from tectonic studies, validating the accuracy of the method.
C. Most importantly, new discontinuities were identified, which could indicate the presence of subsidiary branches or separate buried faults. These findings highlight the necessity of revising and refining the region's seismic hazard zonation maps with higher spatial accuracy.
D. The focus of urban development on geological units with low resistivity (such as clays) and in proximity to these active or buried fault structures significantly increases the dual risks of seismic events and secondary phenomena like liquefaction and landslides.