Processing the Aeromagnetic data in Tehran province and comparison of its results with seismicity and fault trends

Morphologically, the lowest point of Tehran province is located in Varamin city with a height of 749 meters above sea level, and the highest point of the province is located in Tochal Heights with 4375 meters above sea level in Shemiranat city. The mega city of Tehran is also built on the alluvial fans at the foot hill of Alborz mountain, which are located on volcanic-sedimentary rocks of the third geological period (Cenozoic) that during the fourth geological period, it was affected by tectonic activities (Habibi and Horkad, 2014; Ali Beigi et al., 2015). High rates of erosion and sedimentation and urban development cause the destruction or burial of fault structures and their identification sign. Determining the boundary of geological structures is one of the most important and practical issues that has always been discussed in the various sub-branches of the earth sciences, including geophysics (Neawsuparp et al., 2005). Past tectonic earthquake studies have shown that the boundaries of geological structures are mostly identified by faults. In other words, the presence of faults is one of the indicators of active tectonic areas. Therefore, the study of faults to investigate seismicity in connection with the plans for the development of civil activities of cities, industrial towns and the scope of strategic facilities, the investigation of mineral potentials (minerals related to fractures and fault areas) and the detailed understanding of tectonic trends is very important. Here this method is used to calculate the location of seismic events that also presents the seismic nature of the fault processes and its geometry and depth structure in an area.
In addition to reviewing aerial photographs and field survey, studying satellite images is one of the practical methods for identifying the trend of obvious faults and preparing maps of the fault system of different regions. In recent years, preparing airborne geophysical maps for hidden fault structures has become common. On the other hand, one of the most common methods for detecting hidden structures, including faults, is aerial magnetic studies, the interpretation and modeling of which has helped researchers in identifying subsurface faults or possible buried faults.
It is worth mentioning that in some cases the boundary of the structures may not be associated with a fault. Also, there is a possibility that a fault structure does not have a noticeable magnetic signal. Therefore, the results of satellite images or aerial magnetometry do not necessarily lead to the identification of all hidden faults. In this research, it has been tried to process the aerial magnetometer data of Tehran province by different methods (e.g. reduction to the pole, directional derivatives, upward continuation, analytical signal, and horizontal gradient). Then put it on the fault map of the area and comparing the results, the degree of concordance of the trends of the faults in the region with the magnetic anomalies, magnetic bedrock type faults are identified. In the final stage, by placing a new layer of the seismicity map of the region, those active bedrock faults can be identified.
The general results obtained in this research confirm that some of the active faults in the Tehran region are of the basement type, that the ability of these faults to cause large earthquakes is not far from expected, and this result is consistent with other recent seismological studies conducted by Soltani-Moghadam (2016), Ahmadzadeh et al. (2019) and Azqandi et al. (2023) and there is in very good agreement with their finalings.