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Karimzadeh S.,Kanazawa University | Cakir Z.,Technical University of Istanbul | Osmanoglu B.,University of Alaska Fairbanks | Schmalzle G.,University of Washington | And 3 more authors.
Journal of Geodynamics | Year: 2013

We present the surface deformation along the North Tabriz Fault (NTF) deduced from Synthetic Aperture Radar Interferometry (InSAR) technique. The NTF, a major right-lateral strike-slip fault within the active Arabia-Eurasia collision zone, is located 40-45. km southwest of the Mw 6.5 and Mw 6.3, August 11, 2012 earthquake sequence that caused heavy damage and more than 300 deaths in Ahar, NW Iran. InSAR time series analysis of 17 ENVISAT radar images acquired between 2004 and 2010 using combination of the permanent scatterers InSAR (PSI) and the small baseline InSAR (SBAS) approach reveals sub-centimeter interseismic strain accumulation across the NTF and rapid subsidence in the Tabriz basin. Elastic dislocation modeling of the mean line-of-sight velocity field estimated from SBAS time series yields an average slip rate of 8.7 ± 2.5. mm/year with a locking depth of 15.8 ± 10.8. km. This rate is consistent with previous geodetic estimates based on recent Global Positioning System measurements, and suggests a recurrence interval of 250-300 years for major earthquakes of Mw 7.0-7.3 on the NTF, much shorter than those estimated from paleoseismic investigations (821 ± 176 years). This in turn implies a high seismic potential on the NTF taking into account the occurrence of the two last earthquakes on the NTF in 1721 and 1780. SAR time series analysis also reveals three regions of rapid subsidence with a maximum rate of 20. mm/year near the Tabriz thermal power plant in the Tabriz basin. Piezometric data from groundwater wells suggest that accelerated subsidence over the last several years may result from fluctuations in the ground water table. © 2013 Elsevier Ltd.

Moazezi S.,Islamic Azad University at Tehran | Zomorrodian H.,Islamic Azad University at Tehran | Siahkoohi H.R.,University of Tehran | Azmoudeh-Ardalan A.,University of Tehran | And 2 more authors.
Journal of Geodesy | Year: 2016

In this paper, we presented a fast unified method to compute the gravity field functionals and their directional derivatives up to arbitrary orders on nonequispaced grid points at irregular surfaces using ultrahigh-degree models. The direct spherical harmonic synthesis (SHS) for computing the gravity field functionals at arbitrary locations through the Legendre functions is a time-consuming task for high-order and -degree models. Besides, to compute the derivatives of SHS in terms of latitude, the derivatives of the Legendre functions are needed. Therefore, we used Fourier coefficients of Wigner d-functions to compute the directional derivatives of SHS up to arbitrary orders. We also showed that these functions and their derivatives up to order 2 are stable up to ultrahigh-degree (Formula presented.) using extended double precision (i.e., 80 bits variables). Although 2D-FFT can accelerate the computation of global SHS (GSHS), it restricts the results on equispaced grid points. Hence, we used the nonequispaced FFT (NFFT) for computing GSHS on irregular grid points on the sphere that it is the fast nonequispaced GSHS (NGSHS). For maximum degree N and computing points of (Formula presented.) with arbitrary locations, the direct computation methods have the complexity of (Formula presented.). But the presented algorithm with and without precomputed Fourier coefficients of Wigner d-functions has the complexity of (Formula presented.) and (Formula presented.), respectively, where s is cutoff parameter of convolution in NFFT. Using a convolution technique in frequency domain, the NGSHS on the ellipsoid was computed. For computation the gravity field functionals by the NGSHS at irregular surfaces, we defined the Taylor expansion and the Padé approximation both on the sphere and on the ellipsoid. The results showed that the constructed Padé approximation on the ellipsoid provides better accuracy. Finally, we showed that the introduced unified algorithm achieves the required accuracy and that it is faster than direct computations. © 2016 Springer-Verlag Berlin Heidelberg

Ardalan A.A.,University of Tehran | Ardalan A.A.,National Cartographic Center | Rezvani M.-H.,University of Tehran
IEEE Transactions on Aerospace and Electronic Systems | Year: 2015

Multiple Global Navigation Satellite System (GNSS) antennae systems have been among the well-known approaches to attitude determination of moving platforms in recent years. However, the constraints on the onboard GNSS antennae configuration, that is, installing the antennae baselines along the main axes of the platform, can lead to practical difficulties and inevitable uncertainty. In this contribution we present an iterative method to obtain the accurate attitudes by means of the onboard misaligned baselines. In order to remove the effects of the horizontal and vertical misalignments from GNSS observations of the baselines, attitude-induced corrections have been developed through the relative lever-arm coordinates of the onboard antennae. This approach provides us with more freedom from spatial distribution of the onboard antennae. The performance of the proposed method has been analyzed by simulated data and an actual experiment in low- and high-dynamic situations. The simulation has been designed to evaluate the capability and reliability of the iterative method under the presence of small and large misalignments. The field experiment was carried out in the offshore waters of Kish harbor using three dual-frequency GNSS receivers with choke-ring antennae onboard a survey vessel, which was also equipped with an inertial measurement unit (IMU). The maximum allowable misalignments, the convergence of the iteration, and the advantage of the proposed method over the trigonometric approach in spite of applying the traditional calibration are presented. The long-term stability of GNSS attitude determination as well as IMU accuracy degradation, due largely to the increase in the time-varying biases/noises, have demonstrated the potential of the method to estimate the accuracies and biases of the onboard inertial sensor. The overall results affirm that the presented method can effectively provide the platform attitudes using the misaligned GNSS baselines with as much flexibility as possible for the onboard antennae configuration. © 1965-2011 IEEE.

Matkan A.A.,Shahid Beheshti University | Hajeb M.,Shahid Beheshti University | Sadeghian S.,National Cartographic Center
Photogrammetric Engineering and Remote Sensing | Year: 2014

This paper presents a method for road extraction from lidar data based on SVM classification. The lidar data are used exclusively to evaluate the potential in the road extraction process. First, the SVM algorithm is used to classify the lidar data into five classes: road, tree, building, grassland, and cement. Then, some misclassified pixels in the road class is removed using the road values in the normalized Digital Surface Model and Normalized Difference Distance features. In the postprocessing stage, a method based on Radon transform and Spline interpolation is employed to automatically locate and fill the gaps in the road network. The experimental results show that the proposed algorithm for gap filling works well on straight roads. The proposed road extraction algorithm is tested on three datasets. An accuracy assessment indicated 63.7 percent, 60.26 percent and 66.71 percent quality for three datasets. Finally, centerline of the detected roads is extracted using mathematical morphology. © 2014 American Society for Photogrammetry and Remote Sensing.

Shirzaei M.,German Research Center for Geosciences | Walter T.R.,German Research Center for Geosciences | Nankali H.R.,National Cartographic Center | Holohan E.P.,German Research Center for Geosciences | Holohan E.P.,University College Dublin
Geology | Year: 2011

The detection and monitoring of gravity-driven volcano deformation are vital for understanding volcanic hazards such as landslides, lateral blasts, and debris avalanches. Although deformation has been detected at several large active volcanoes (e.g., Mount Etna, Vesuvius, Kilauea), these systems also exhibit persistent magmatic activity, obscuring the gravity-driven signals of ground motion. In this study we present a first interferometric synthetic aperture radar (InSAR) deformation time series at the dormant Damavand volcano in northern Iran, over the period A.D. 2003-2008. The high-resolution data show a lateral extension of the volcano at the relative rate of as much as ~6 mm/yr accompanied by subsidence at the rate of as much as ~5 mm/yr at the volcano summit. We find that lateral motion of the east flank is more significant than that of the west flank. On the basis of past understanding and modeling of deforming volcanoes elsewhere, we interpret this new evidence to reveal long-term, slow, gravitydriven deformation, possibly in the form of gravitational spreading, at Damavand. This persistent deformation activity is well expressed, although no volcanic activity was ever reported in history. This finding shows that magmatic activity is not required for spreading and highlights the importance of identifying long-lived gravity-driven deformation for hazard assessment at dormant or inactive volcanoes. © 2011 Geological Society of America.

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