Introduction

The solid crust of the earth is not fixed during geological history, but is constantly changing its shape under the influence of internal and external factors. These elevation changes in the form of subsidence and uplift have significantly increased the trend of environmental hazards, and the effect of these hazards causes severe damage to the natural environment and human complications (Zare Kamali et al., 2016) based on the definition of the United States Geological Institute. In America, the phenomenon of land subsidence includes the collapse or downward subsidence of the earth's surface, which can have a small displacement vector and occurs gradually and instantaneously on a large scale (US Geological Survey, 2011). The most important cause of regional subsidence of the earth's surface In the sedimentary basins of arid and semi-arid regions, the compaction of sediments is due to excessive extraction of groundwater resources (Zhou et al., 2015). The phenomenon will be seen more widely and more acutely (Liu et al., 2006). Land subsidence usually occurs with a time delay after the long-term extraction of underground water sources (Scott, 1979). The amount of subsidence depends on the thickness and compressibility of the layer It depends on the length of loading time, degree and type of stress



Methodology

The current research is of an applied type and its research method is an analysis based on the integration of data analysis, geographic information system and the use of multi-criteria analysis techniques. GIS Arc, Ecognition ENVI, Idrisi and Excel software have been used for image processing and data analysis. In this research, in order to investigate the relationship between the subsidence of the studied area and the condition of underground water resources, the groundwater loss was investigated. In order to zone the risk of subsidence, in the stage of data collection, first the influencing components should be determined and based on them, the required data and information should be collected and classified. For this purpose, in this study, first the effective factors (including: slope, lithology, land use, precipitation, distance from the city and village, distance from the river, distance from the fault and drop in the underground water level), by examining the sample of studies conducted in relation to With the risk of subsidence, which has been done by other researchers and they have stated the effective factors in causing subsidence.



Results and Discussion

The criteria of water level drop, land use, slope and geology received the most weight and importance and considering that in the weighting of Kartik, the weight of the criteria, according to the criteria maps and the degree of correlation, contrast and the standard deviation between the used information layers is determined, the use of this method in the weighting of the criteria in the current research can solve the problem of the independence of traits from each other, which occurs during pairwise comparisons within the framework of the chain analysis process method. There are hierarchies and process of network analysis to solve. According to the output from the application of the mentioned techniques and finally (Figure 8) the subsidence zoning map with Kodas and Mobak techniques, it can be said that in the Mobak technique, 284.18 square kilometers of the area of the zone are in the very high risk class and 14 223.2 square kilometers is in the high risk class, and in the KODAS technique, 236.09 square kilometers of the range area is in the very high risk class and 512.34 square kilometers is in the high risk class (Tables 7 and 8). A large part of the high-risk and high-risk class in the area of Karaj, Saujblag and Nazarabad cities in terms of the possibility of subsidence in the northern part of the range (Afsharieh, Hakimiyeh, Hamidiyeh and Sohilieh farms), northwest (Lashkar Abad, Qohe and Ramchin, Mohammad Abad Afshar) , Sanqarabad) and the central part (Mehrshahr, Golshahr, Rajaeeshahr, Khorram Dasht and Kamalabad (Kamalshahr)). In addition, according to the zoning map of the subsidence risk potential in the south and southwest part of the area in the urban area of Mahdasht Rashte, Sardar Abad, Ahmed Abad; Meshkin Abad and Abbas Abad, Sardar Abad, Shahrak Ba'ath and Mohammad Abad are numerous. A part of the southeastern part of Karaj Plain, including Amirabad, Kohak, Abu Dhar and Garmdara, and the western part of Nazarabad are also in the high and very high risk category.



Conclusion

In fact, the obtained results indicate the conformity of the groundwater level drop with the amount of subsidence and in the areas where the water level has dropped the most. According to the results of zoning the risk of sales; The criteria of water level drop, land use, slope and geology are the most important factors involved in creating the risk of subsidence in the study area, with weight coefficients of 0.151, 0.147, 0.43 and 0.136, respectively. Also, using the relative performance detection curve of the ROC chart comparing two techniques, it was observed that the accuracy of the Mabak method in this research is in the very good category and the accuracy of the Kodas method is in the good category. According to the obtained results, it can be said that the most important main factor involved in increasing the amount and potential of subsidence in the study area is the excessive exploitation of underground water and the drop in the water level.