Earth surface deformation analysis of 2005 Qeshm earthquake based on three-dimensional displacement field derived from radar imagery measurements

Abstract

We derived the 3D vector displacement field due to the 5.9Mw Qeshm island (Iran) earthquake using ascending and descending interferograms and azimuth offsets obtained from ENVISAT ASAR data. The pick-to-pick estimated displacement was 10cm in west, 69cm in south and 22cm in vertical directions. We then used strain analysis to study coseismic surface deformation of the earthquake. Finite differences and finite element as two numerical solutions were applied in order to compute the strain tensors. Furthermore, dilation and shear parameters were derived using the strain tensors. Finite differences results showed the maximum expansion of 0.002 and maximum contraction of 0.003. The amounts of maximum shear in xy, xz and yz planes were estimated using finite differences method as 0.05, 0.1 and 0.049, respectively. The maximum expansion and contraction were computed as 0.006 and 0.005, respectively, using finite element approach. Moreover, the maximum shear in xy, xz and yz planes obtained by finite element method was 0.2, 0.4 and 0.19, respectively.Comparison of the two numerical methods shows that the numerical results obtained by the finite differences method are more accurate due to the use of more adjacent and more points to calculate the strain tensor. However, the results of both methods represent the changes and maximum expansion and contraction in the direction of faults proposed by after shock seismicity study of the earthquake.The concentration of the shear and dilation were observed in the central part of the island along the NW-SE oriented fault passing from central part of the island and also we have considerable amount of shear and dilation in the vicinity of Qeshm fault.