تحلیل حرکت گسل ها با استفاده از تصاویر راداری، مطالعه موردی گسل انار

Introduction

Monitoring the dynamic behavior of faults can play an important role in predicting the imminence of earthquakes (Bernhart et al., 2020; Chin et al., 2020). So far, various methods have been used to investigate the activity of faults, among which we can mention the investigation of geomorphological evidence, structural analysis and paleoseismology. Nowadays, with the advancement of remote sensing science, especially in the field of radar imaging, a new gate has been opened to study the movements of the Earth's crust. The use of radar interferometric methods in the field of studying faults, earthquakes, subsidence and other natural hazards is expanding day by day. Considering the ability of radar images to determine the amount of changes and displacements that have occurred on the surface of the earth in a certain period of time, these images can be used to monitor the changes that have occurred on faults. Monitoring the displacement rate occurring on the fault plates can help in predicting possible. Accumulated displacements on the faults eventually cause the displacement of the main fault planes. In this article, the deformations and displacements that occurred in the area of Anar fault were monitored using the PSI method in a period of 3 years, and it was also tried by monitoring the change in the concentration of radon gas dissolved in the water of wells in the area. To investigate and analyze the activity level of the said fault.



Methodology

In this research, from 148 sensor images of Sentinel 1 of the European Space Agency's Soyuz satellite with SLC format of IWS mode type with VV polarization, related to the dates 01/17/2019 to 05/03/2022. These data have been converted into single-view images, and their information has not been distorted in any way. These images were made available through the Copernicus website.

Permanent scatterers are complications whose distribution characteristics are constant over time and do not suffer from time correlation. These effects, which are mainly man-made structures, do not suffer from time correlation. There are pixels in which one scatterer dominates in that pixel and behaves like a permanent point scatterer. Therefore, the amount of non-correlation is significantly reduced. Using the technique of permanent scatterers, it is possible to measure sub-centimeter displacements. For this purpose, by using the sentinel images obtained from the studied area, an interferogram was prepared, after that the permanent scattering points were identified and finally, the amount of displacement in the direction of the satellite view corresponding to each of these points was measured. It is taken.



Results and Discussion

By performing the PSI method on the interference maps, 2340 and 2462 points were identified and selected as permanent scattering points for low-pass and high-pass images, respectively, in the study area. Then the displacement of these points was calculated. The map of the location of these points and their displacement can be seen in Figure 6. As can be seen in this figure, the displacement along the line of sight of the satellite of the permanent scattering points varies from +5 mm to 15 mm. The displacements are in the direction of the satellite's view, so that positive numbers indicate the approach of the surface to the satellite and rise, and negative numbers indicate the distance of the surface from the satellite and subsidence. The red points located in the studied area have subsided more than 15 mm during one year. As can be seen in Figure 6, there are two large subsidence areas on both sides of the Anar fault, with an area of about 80 and 16 square kilometers, which are almost logical for agricultural gardens, considering the existence of the phenomenon of subsidence in most plains of Iran. As a result of the excessive extraction of underground water sources, the aforementioned subsidence ranges can be considered as the result of this phenomenon. The preparation of the groundwater level drop map in the studied area, using the data related to the number of 40 wells during the years 2019 to 2021, and its adaptation on the displacement map, confirms the mentioned issue well.

the offset rate obtained from high-pass data and low-pass data varies between 7 and 7 mm per year. A three-dimensional map of displacement in the fault area was prepared by combining the observations along the azimuth and the observations along the line of sight of the satellite. Based on this, the displacement rate of the east-west component was estimated between 2 and 2 mm per year, the displacement rate of the north-south component was between 6 and 6 mm per year, and the displacement rate of the vertical component was estimated between 2 and 4 mm per year.



Conclusion

The monitoring of the movements that occurred in the area of the Anar fault shows that it is active. The results obtained from the PSI method showed that the displacement rate occurring on the surface of the earth is constantly increasing. Determining and calculating the maximum displacement rate for the north-south component compared to other three-dimensional displacement components, the type of movements occurring on both sides of the fault line, and how the profiles related to the three-dimensional displacement components are all indicative of slip extension and Anar fault is right-sliding, also the time series analysis of the points located on the fault blocks shows an increasing rate of movement of the fault blocks during the study period.





Keywords: Azimuth offset, three-dimensional displacement, Sentinel 1, Anar fault.