Farokh Tavakoli

Present-day kinematics and fault slip rates in eastern Iran, derived from 11 years of GPS data

We analyze new GPS data spanning 11 years at 92 stations in eastern Iran. We use these data to analyze the present-day kinematics and the slip rates on most seismogenic faults in eastern Iran. The east Lut, west Lut, Kuhbanan, Anar, Dehshir, and Doruneh faults are confirmed as the major faults and are found to currently slip laterally at 5.6 ± 0.6, 4.4 ± 0.4, 3.6 ± 1.3, 2.0 ± 0.7, 1.4 ± 0.9, and 1.3 ± 0.8 mm/yr, respectively. Slip is right-lateral on the ~NS striking east Lut, west Lut, Kuhbanan, Anar, and Dehshir faults and left-lateral on the ~EW Doruneh fault. The ~NS faults slice the eastern Iranian crust into five blocks that are moving northward at 6–13 mm/yr with respect to the stable Afghan crust at the eastern edge of the collision zone. The collective behavior of the ~NS faults might thus allow the Arabian promontory to impinge northward into the Eurasian crust. The ~NS faults achieve additional NS shortening by rotating counterclockwise in the horizontal plane, at current rates up to 0.8°/Ma. Modeling the GPS and available geological data with a block rotation model suggests that the rotations have been going on at a similar rate (1 ± 0.4°/Ma) over the last 12 Ma. We identify large strains at the tips of the rotating east Lut, west Lut, and Kuhbanan faults, which we suspect to be responsible for the important historical and instrumental seismicity in those zones.

The kinematics of the Zagros Mountains (Iran)

Abstract We present a synthesis of recently conducted tectonic, global positioning system (GPS), geomorphological and seismic studies to describe the kinematics of the Zagros mountain belt, with a special focus on the transverse right-lateral strike-slip Kazerun Fault System (KFS). Both the seismicity and present-day deformation (as observed from tectonics, geomorphology and GPS) appear to concentrate near the 1000 m elevation contour, suggesting that basement and shallow deformation are related. This observation supports a thick-skinned model of southwestward propagation of deformation, starting from the Main Zagros Reverse Fault. The KFS distributes right-lateral strike-slip motion of the Main Recent Fault onto several segments located in an en echelon system to the east. We observe a marked difference in the kinematics of the Zagros across the Kazerun Fault System. To the NW, in the North Zagros, present-day deformation is partitioned between localized strike-slip motion on the Main Recent Fault and shortening located on the deformation front. To the SE, in the Central Zagros, strike-slip motion is distributed on several branches of the KFS. The decoupling of the Hormuz Salt layer, restricted to the east of the KFS and favouring the spreading of the sedimentary cover, cannot be the only cause of this distributed mechanism because seismicity (and therefore basement deformation) is associated with all active strike-slip faults, including those to the east of the Kazerun Fault System.

Interseismic deformation of the Shahroud fault system (NE Iran) from space‐borne radar interferometry measurements

The Shahroud fault system is a major active structure in the Alborz range of NE Iran whose slip rate is not well constrained despite its potential high seismic hazard. In order to constrain the slip rate of the eastern Shahroud fault zone, we use space-borne synthetic aperture radar interferometry with both ascending and descending Envisat data to determine the rate of interseismic strain accumulation across the system. We invert the slip rate from surface velocity measurements using a half-space elastic dislocation model. The modeling results are consistent with a left-lateral slip rate of 4.75 ± 0.8 mm/yr on the Abr and Jajarm, strands of the Shahroud fault, with a 10 ± 4 km locking depth. This is in good agreement with the 4–6 mm/yr of left-lateral displacement rate accumulated across the total Shahroud fault system obtained from GPS measurements.

Multivariate statistical analysis of deformation tensors: independent vs. correlated tensor observations

In the presence of errors in measuring a random displacement field (under the normal distribution assumption of displacement field), stochastic behaviors of principal components of deformation tensors (strain tensor and tensor of change of curvature (TCC)), based on the intrinsic assumption of geometrical modeling of surface deformation analysis, are discussed. We divided the contents into two parts: In the first, we considered independent random vectors of repeated tensor measurements. In the second step, we considered correlations among repeated measurements. Then, covariance components between tensor elements by Helmert estimator, based on prior information of variance components, are estimated. As a case study, both assumptions are applied to the estimation of principal components of deformation rate tensor observations in Zagros region (Western Iran). The results of numerical analysis showed that greatest shortening is accommodated in oblique orientation (NS) with respect to the Main Recent Fault (MRF), northwest part of North Zagros, Central Iran block and MRF, respectively. Most of the extensions occurred in the east part of the belt. The pattern of eigenspace components of TCC shows highest positive values across the NW region, nearly in orthogonal direction to the MRF and Main Zagros Fault (MZF). The pattern has insignificant values in the Central Zagros. It takes the significant negative values across the SW part, especially along the SPF and Persian Gulf shore. The effect of non-independent observations on the estimation of eigenspace components of deformation tensors (strain tensor and TCC) shows that the estimation of covariance components has influence on the confidence intervals of eigenspace components, especially in seismically active regions of the belt (along the Persian Gulf shore, NW of the belt and region between the Central Iran block and MRF). The results demonstrate the importance of considering the correlation structure among the observations on statistical behavior of principal components of deformation tensors in seismically active regions.