In recent years, land subsidence creates a serious environmental disaster in various places of the Iran. Land subsidence is a geomorphic phenomenon that caused by several factors; sometimes it is influenced by natural factors but in many cases occurs due to human intervention specially uncontrolled exploitation of groundwater from aquifers. There are several methods to measure the land subsidence including the use of GPS (Global Positioning System), the precise leveling and remote sensing techniques, particularly Interferometric Synthetic Aperture RADAR (INSAR) method. Between these methods, the INSAR technique is the sufficient method for ground surface deformations. In this research, the land subsidence phenomenon in Gorgan has been investigated by the INSAR technique using ENVISAT radar images. Gorgan is the capital of Golestan province in Northeast of Iran. The tectonic situation of the studied area is very complex; this area is located between the uplifting Kopeh-Dagh belt to the West, subsiding South Caspian region to the east and uplifting Alborz mountain range to the South. The results show that the north of Gorgan has experienced subsidence in the period of 2007/01/26 to 2009/12/11 (34 months and 15 days). The subsided area has almost east– west trend which is consistent with the trend of tectonic structures. The amount of displacement is calculated about 4. 8 cm. The graphs of the rainfall and groundwater level changes with time in Gorgan for the period of 2007/01/26 to 2009/12//11 show a downward trend, despite of seasonal fluctuations. The consequences of this decline in groundwater levels may lead to land subsidence in the study area.

Blemish of subsidence and land ruptures such as destroying aquifer systems, damaging structures and disordering water main, are usually irreparable and expensive. One of the regions with a high rate subsidence in Iran is the Yazd-Ardakan plain that subsides with a maximum rate of 12 cm per year based on levelling and INSAR observation. It is obvious that such a high rate subsidence is the result of water extra exploiting and groundwater levels at piezometric wells confirm this in the region. Management of water drafting in this region is a necessary work in this region.

Today's digital elevation models have many applications in various fields including engineering projects and management of natural resources and etc. One of these applications is a topographic correction in INSAR to find the amount and rate of displacements. The purpose of this paper is to compare the effects of two digital elevation models with a resolution of 30 m and 90 m in order to obtain displacement rates from radar images. Persist Scatterer and Small Baselines methods were used to compute the displacement rate in the region. Processing was performed with both models SRTM and ASTER. The maximum difference between the results from two elevation models is observed in areas with a high elevation difference. In both methods, the number of persist scatterers in the case of model ASTER is less than model SRTM. In areas with low elevation differences, the results of two elevation models are very similar to each other. But in areas with high topography, the low resolution elevation model does not have the ability to deliver results with appropriate accuracy. In PS method there are 0.2 mm difference in maximum and 1.1 mm in minimum of displacement rate field and in Small Baselines method, these rates were 4 and 1 mm respectively. In order to better evaluate the results, six points in the region were examined. The maximum difference between the results was 4 mm. This difference is significant at the ten percent level of confidence. As a result, in areas of high topography, it is necessary to use the more accurate digital elevation model to achieve higher accuracy.

ABSTRACT Various natural phenomena have had a significant impact on the quality of human life since long ago. One of these types of natural phenomena is the deformation and displacement of the earth's surface, including subsidence. Subsidence is a morphological phenomenon that occurs under the influence of the downward movement of the earth. The salient features of radar images and the acceptable accuracy of the radar interferometric method have provided a powerful tool for researchers in investigating land subsidence. For this reason, 35 radar images of the Sentinel 1 sensor in the ascending orbit and transit 174 in the period from 2016 (June) to 2021 (January) were used to investigate the land subsidence in the Kermanshah plain. To analyze the time series of these images to prepare the average annual subsidence map in the plain, the radar interferometric technique was used under PSI and SBAS approaches. The results show the maximum land subsidence of 100 mm in the SBAS method and 10 mm in the PSI method in the west and northwest of the plain for 6 years. Finally, the maximum range was investigated in terms of geology and geo-hydrology. The results of the investigations showed that the land use of the maximum land subsidence area includes irrigated and rainfed agricultural lands, with the highest amount of water withdrawal in the agricultural sector, along with an average drop in the water level of 8 meters in 20 years in wells with a large thickness of fine-grained sediments. Is. In general, land subsidence in the area is affected by human and natural factors Extended Abstract Introduction Studying and monitoring the displacement field caused by the changes in the shape of the earth's surface is one of the essential and practical studies in various topics such as geology, geomorphology, and geophysics.In the meantime, land subsidence is one of the destructive geological phenomena that can cause irreparable financial and human losses. In fact, land subsidence is a type of change in the shape of the earth's surface, which is associated with a vertical deformation or downward movement of the earth's surface so that the surface materials settle gradually or precipitately. This phenomenon is a problem and a danger threatening global societies.The phenomenon of subsidence can have surface morphological effects. For this purpose, identifying and reducing the consequences of the subsidence phenomenon requires a monitoring system. In order to evaluate and accurately measure this phenomenon, several methods have been presented, and the radar interferometry technique was introduced as one of the methods of processing radar images in active remote sensing, a useful tool in monitoring the displacements of the earth's surface. So that for several years, the salient features of radar images and the acceptable accuracy of radar interferometric methods have provided researchers with a powerful tool for investigating land subsidence. For this reason, 35 radar images of the Sentinel 1 sensor in the ascending orbit and transit 174 from 2016 (June) to 2021 (January) were used to investigate the land subsidence in the Kermanshah plain.In order to analyze the time series of these images to prepare the average annual subsidence map in the plain, radar interferometric technique was used under PSI and SBAS approaches.   Methodology Artificial aperture radar interferometry is a remote sensing technique. Two or more radar images are used to produce a digital elevation model or prepare a land surface displacement map. In this technique, the phase difference between two waves is measured, which is attributed to the change in the distance between the sensor and the ground target or the displacement of the ground surface. Currently, there are three general methods for limitations and analysis of interferometer time series, which are hybrid, small baseline length, and permanent scatters. In the following article, the time series of the land subsidence phenomenon in Kermanshah Plain is monitored and measured using radar data, radar interferometry technique, and time series analysis of small baseline and persistent scatterers.In the small baseline method, only pairs of images are used whose vertical component is less than the critical value of the baseline. Also, their time baseline should be minimum at the same time. In this way, only interferograms with suitable quality are formed. In the method of persistent scatterer, the selection of permanent scattered pixels with constant scattering behavior in time can eliminate the limitations of the traditional radar interferometry method, and the possibility of measuring the displacement of the earth's surface even provided a few mm. Then, the results of these two methods, which are the average annual subsidence map in the desired time period, are examined in order to explain the connection and cause of the subsidence that occurred on the level of the plain, hydrogeological, and geological data.   Results and discussion In order to investigate the behavior pattern of the earth's surface in the long term, time series analysis methods were used using a small baseline and persistent scatterer. To accomplish this task, among the many images and interferograms, 35 radar images from the Sentinel 1 sensor were selected in the period from 2016 (June) to 2021 (January), and 88 interferograms that had a suitable spatial and temporal baseline were selected using the lowest baseline method. Thirty-three interferometers were selected in the method of the persistent scatterer, and they were covered in the interferometry process. After obtaining the interferogram images, the noises in the interference mapping should be removed so that the remaining noise is only caused by the earth's surface's displacements, resulting in the average map of the displacements of the earth's surface in the desired time period. The evaluation of the map obtained in the small baseline method indicates maximum subsidence of 100 mm per year and 10 mm in the persistent scatterer method in the western and northwestern parts of the plain. Finally, the hydrogeological data (number of wells allowed, type of consumption, amount of harvesting, drop in the level of piezometer wells) and geology (geological log of wells) and land-use of the plain were investigated in order to investigate the cause of subsidence in the plain. These surveys showed the impact of human and natural factors' impact on the subsidence in the plain.   Conclusion In this research, the time series of land subsidence in Kermanshah plain was measured in 2016 (June)-2021 (January) with two approaches, small baseline, and persistent scatterer. The results of the two-timeseries show the maximum land subsidence of 100 mm per year in the SBAB method and 10 mm per year in the PS method in the western and northwestern parts of Kermanshah Plain. In the maximum range, the number of wells has a high density, and most of the wells' water extraction is for the agricultural sector. The land use map of the region also confirms that the maximum land subsidence area has 62% (911 km) area of the plain. The selected wells evaluated in the maximum range of land subsidence also show the amount of water level drop 8 meters per year. From the point of view of geology, these wells have the thickness of sediments, which is about 20 to 37 meters. These cases express the conclusion that the area is affected by human factors (land use, indiscriminate extraction from the surface of the well, number of wells) as an aggravating factor and natural factors (reduction of atmospheric precipitation, continuation of drought, type of sediments on the plain) in next to each other has caused subsidence phenomenon.   Funding There is no funding support.   Authors’ Contribution All of the authors approved thecontent of the manuscript and agreed on all aspects of the work.   Conflict of Interest Authors declared no conflict of interest.   Acknowledgments We are grateful to all the scientific consultants of this paper.

Interferometric synthetic aperture radar (INSAR) time series is a technique to evaluate earth surface deformation over large areas. One of the INSAR time series algorithms is small baseline subset (SBAS) method that has been successfully used for monitoring deformation. Noise assessment and spatiotemporal evaluation of deformation time series is an important factor in understanding and interpreting deformation in the study area. In this paper, we used SBAS interferometry method for extracting deformation time series caused by land subsidence in the Mahyar plain in Isfahan province of Iran. Noise structure of the deformation time series is then estimated with using multivariate w-test statistics. This assessment leads to estimate parameters of deformation time series realistically. Moreover, the results show that overall-time series do not provide new information about deformation in study area, according to spatial correlation among neighbor pixels.

Phase unwrapping is one of the most important parts of INSAR techniques. In order to estimate the grand surface displacements, interferomtric phases modulated between 0 to 2π must be unwrapped. Based on the use of either the conventional method or persistent scatterer (PS), phases will be spread both regularly and irregularly. The phases of PSs can be unwrapped by reducing phases into a regular and continues grid with neatest neighbor interpolation method. In this paper, beside Minimum Cost Flow (MCF) as a global unwrapping method, three local unwrapping methods (Branch-cut, Phase Derivative Variance and Branch cut-Phase Derivative Variance) are introduced as well. These conventional unwrapping approached are implemented on an irregular interferogram processed from Sentinal1A satellite images acquired over the Sirjan basin. At the end, the results of these approaches are assesed with unwraped phase which is resulted in a conventional interferogram unwrapped with MCF method.

The Ghotor doublet earthquake happened on 23 Feb 2020 near Khoy and Salmas cities in west Azerbaijan province of Iran near Iran-Turkey border. The first large event with a magnitude of 5. 8 Mww (USGS) happened at 5: 52 UTC (9: 23 AM local time) and followed by a second large event of magnitude 6. 0 Mw (USGS) at 16: 00 UTC. The second event inflicted most of the building damages. No surface rupture has been reported for the events. We estimated the areal extent of the surface displacement related to the 2020 Ghotor doublet earthquakes using three sets of C-band imagery from the European Space Agency Sentinel 1A and 1B satellites. Due to small ground displacement, we could not model the fault geometry of the first mainshock. The ascending and descending displacement maps of the second main shock are used to jointly invert the causative fault plane parameters. To obtain the source parameters, we first down-sampled the unwrapped LOS surface displacements by a quadtree algorithm and then inverted the unwrapped interferograms to infer the geometry of a single rectangular plane with uniform slip in a uniform elastic half-space. The fault geometry parameters are location (X, Y, and Depth), size (length and width), orientation (strike, dip, and rake), and uniform slip of the rupture plane. We assume the X, Y, and depth to correspond to the center of the top edge of the rupture plane. We used a nonlinear inversion method as implemented in the open-source software called Geodetic Bayesian Inversion Software (GBIS) released by Centre for Observation and Modeling of Earthquakes, Volcanoes, and Tectonics (COMET). We used Okada‘s (1985) displacement green functions to model the displacement field. The calculated optimal model illustrates a northeast-striking (N24°) left-lateral rupture plane dipping ~86° towards the west. Once the geometry of the fault plane with uniform slip was estimated, we expanded the rupture plane 20 km along-strike and 12 km along down-dip directions and divided it into 1291 individual patches to obtain the distributed slip on the rupture plane. Each patch has a fixed geometry according to optimal source parameters obtained from the nonlinear modeling, and the slip was allowed to vary freely on the fault plane. We used a modified version of the open-source software called FaultResampler 1. 4 to apply the linear inversion for calculating slip distribution on the rupture plane. The coseismic rupture concentrates around a center depth of 3 km with a maximum slip of 97±8 cm. Assuming a rigidity modulus of 30 GPa, the geodetic moment is estimated to be 1. 517E+18 Nm, equivalent to a moment magnitude of 6. 05 Mw.