InSAR-derived surface Deformation of the April 2021 Genaveh Earthquake evidence of progress of the Quaternary Zagros Mountain front

Bandar Genaveh earthquake accured in the foredeep of Zagros, as it is one of the most active seismic belts of fold and thrust belt in quaternary (Etemad-Saeed et al., 2020). Major deformation in this zone is caused by the development of blind thrust which cause the growth of folds and the subsequent increase and intensity of orogeny (Berberian 1995). The main purpose of this research is to investigate the vertical surface changes associated with the earthquake using the Sentinel 1 satellite radar.The area affected by the earthquake includes a series of double-plunge folds, extending northwest-southeast.This area is located on BolKhari anticline with the northwest-southeast extension as one of the surface deformations in the foredeep of the Zagros orogenic belt (Sanaei et al. 2019).

In order to calculate the amount of vertical displacement during an earthquake, two radar images of the Sentinel 1 satellite with IW mode on April 14 and 26 have been used (https://sentinel.esa. int/web/sentinel/missions/sentinel-1). Each Sentinel 1 image has three IWs and each IW contains 9 bursts. The studied area is covered by IW3 and parts 6 to 8 of the obtained images. The extraction process of vertical displacement was done using SNAP (https://step.esa.int/) software.

The output image of the displacement before and after the earthquake shows a surface change with a maximum vertical displacement of 16.5 cm and negative 0.9 cm from the satellite. In other words, the area affected by the earthquake has risen by 16.5 cm and subsided by 0.9 cm. These surface changes are observed in the form of an ellipse with a large diameter extending northwest-southeast and parallel to the Golkhari anticline and at the end of its northwest plunge. This displacement ellipse is spindle-shaped with the elongated part towards the northwest.In order to investigate the changes in the vertical movement of the earth's surface, two profiles were drawn in the two directions of northwest-southeast and northeast-southwest, parallel to the major and minor diameters of the deformation ellipse A-Bprofile along the small diameter shows a subsidence along the northeast and asymmetrical uplift with a lower slope in the northeast and a higher slope in the southwest part. Profile C-D, which is drawn along the southeast-northwest direction and shows a slight subsidence at the southeast end and an asymmetric uplift with a greater slope in the southeast part.In general, the following evidence can be evidence to the progress of the orogenic foredeep towards the southwest and northwest, or in other words, the growth of the Bolkhari anticline in the direction of the northwest caused by growth of a blind trust fault during Genaveh earthquake.1- Displacement profiles show a subsidence in the southeast and northeast and an asymmetric uplift with extension to the northwest and southwest. This displacement can be seen as uplift along with the dextral movement caused by the thrust fault with the progress of deformation or rupture of the fault from the southeast to the northwest parallel to the axis of the anticline.2- The highest uplift has occurred at the end of the northwest plunge of the anticline, which can be seen as evidence of the progress of this plunge towards the northwest.3- The epicenter of the earthquake (USGS as a base) is in the northeast of the displacement ellipse and even other are located either in the southeast or northeast part and indicate the starting point of rupture from these parts to the south and northwest.4- The most destruction and damages are related to the areas and villages located in the northwestern part of the anticline and in the area of the most surface displacement, which are well matched.5- The dispersion of aftershocks shows their concentration on the area with the highest uplift. Other aftershocks with less concentration are scattered in the form of a crescent from the southeast to the northwest and on the northeast slope. This pattern of aftershocks can be an evidence of the existence of the main fault with the northwest-southeast extension with a slope towards the northeast, whose effect started from the northeast and continued parallel to the long axis of the deformation ellipse.6- Almost half of the displacement ellipse is located beyond the mountain-plain border and in the plain's edge, which indicates the uplift of the plain, or in other words, the joining of these parts to the mountain front and the progress of a deformation front.

The radar interferometric analysis shows a vertical surface deformation with a spindle-shaped ellipse parallel to the Bolkhari anticline and with a maximum elevation of 165 mm along the northwest plunge of this anticline and on the border of mountains and plains. Comparing displacement ellipse with mainshock, aftershocks, surface destruction and mountain-plain boundary shows the uplift and progress of the mountain boundary towards the plain in the northwest and southwest with the growth of the Bolkhari anticline.