عنوان مقاله [English]
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The 2012 earthquake of the Ahar and Varzegan (Mw=6.2 and 6.4) and 4 months aftershocks related to these earthqukes was shown the concentration of deformation and stress in the NW of Iran. The study area is a relay tectonically region between an active tectonic fault system, North Anatolian fault system located in Turkey, and the Alborz and Zagros in north and southeast of Iran respectively .The epicentral locations of the main shocks, their mechanisms and aftershock distribution show that the recent large earthquake in Iran, Ahar-Varzaghan earthquake, may have other sources than Tabriz and Ahar faults which are two main active faults in NW-Iran. In order to study these deformations, the results of the GPS geodesy data, tectonic stress that causes the deformations and radar data analysis were researched.
Synthetic Aperture Radar (SAR) is a coherent active microwave remote sensing system that could effectively map the scattering properties of the Earth’s surface and has been already intensively investigated. One of the major applications of the SAR technology is represented by the interferometry (InSAR) technique which exploits, in its basic form, the phase difference of two complex valued SAR images (acquired from different orbit positions and at different times) in order to measure several parameters, such as deformation. But geometrical and temporal decorrelations degrade the accuracy and even sometimes make the measurement impossible in deformation monitoring. Recent developments in differential interferometry have demonstrated some prospective to overcome the above limitations of the conventional interferometry and also for more accurate and temporally dependent results. The new interferometric processing techniques include interferometric stacking and Persistent Scatteres Interferometry. Persistent Scatterer Interferometry is a powerful group of techniques for deformation measuring and monitoring using interferometric SAR imagery. PSInSAR is possible to avoid many of the limitations of conventional method by only analyzing certain pixels which behave like point scatters and retain some degree of correlations. This technique represents an advanced type of Differential Interferometric SAR techniques: it is based on large stacks of SAR images and suitable data modeling procedures that make the estimation of different parameters possible. These parameters include the deformation time series and the average displacement rates.
This research used StaMPS method, for monitoring intersiesmic crustal deformation in Ahar-Varzegan earthquake. In this study we use 20 Envisat ASAR images during the time period of 2003- 2010 to study pre-siesmic deformations over Ahar-Varzegan by persistent scattering interferometry. The ground deformation rate in mm/year along the line of sight direction of satellite is obtained and the results showed that the maximum horizontal displacement rate is equal 7.4 mm/year.
Application of tectonic stress inversion allows determination of a consistent average state of stress in the Ahar south-thrustin which the average stress is characterised by a NW-SE (117˚/16˚) direction of compression (maximum stress). This shows that the maximum stress is roughly horizontal and this is the cause of the formation and development of the thrusting in the west of the Qoshadagh. Stress analysis results, earthquake focal mechanisms, fault mechanism, and GPS geodesy are all consistent by the radar interferometry results.