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  • 1.
    Abdetedal, Mahsa
    et al.
    Institute of Geophysics, Tehran, 14155-6466, Iran.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Institute of Geophysics, Tehran, 14155-6466, Iran.
    Gheitanchi, Mohammad Reza
    Institute of Geophysics, Tehran, 14155-6466, Iran.
    Ambient noise surface wave tomography of the Makran subduction zone, south-east Iran: Implications for crustal and uppermost mantle structures2015In: Earthquake Science, ISSN 1674-4519, E-ISSN 1867-8777, Vol. 28, no 4, p. 235-251Article in journal (Refereed)
    Abstract [en]

    Seismic ambient noise of surface wave tomography was applied to estimate Rayleigh wave empirical Green’s functions (EGFs) and then to study crust and uppermost mantle structure beneath the Makran region in south-east Iran. 12 months of continuous data from January 2009 through January 2010, recorded at broadband seismic stations, were analyzed. Group velocities of the fundamental mode Rayleigh wave dispersion curves were obtained from the empirical Green’s functions. Multiple-filter analysis was used to plot group velocity variations at periods from 10 to 50 s. Using group velocity dispersion curves, 1-D v S velocity models were calculated between several station pairs. The final results demonstrate significant agreement to known geological and tectonic features. Our tomography maps display low-velocity anomaly with SW-NE trend, comparable with volcanic arc settings of the Makran region which may be attributable to the geometry of Arabian Plate subducting beneath the overriding the Lut block. The northward subducting Arabian Plate is determined by high-velocity anomaly along the Straits of Hormuz. At short periods (<20 s), there is a sharp transition boundary between low- and high-velocity transition zone with the NW trending at the western edge of Makran which is attributable to the Minab fault system.

  • 2.
    Abdollahi, Somayeh
    et al.
    Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Ardestani, Vahid Ebrahimzadeh
    Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Zeyen, Hermann
    Univ Paris Saclay, Univ Paris Sud, CNRS, GEOPS, F-91405 Orsay, France.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Crustal and upper mantle structures of Makran subduction zone, SE Iran by combined surface wave velocity analysis and gravity modeling2018In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 747, p. 191-210Article in journal (Refereed)
    Abstract [en]

    The inversion of Rayleigh wave group velocity dispersion curves is challenging, because it is non-linear and multimodal. In this study, we develop and test a new Rayleigh wave dispersion curve inversion scheme using the Shuffled Complex Evolution (SCE) algorithm. Incorporating this optimization algorithm into the inverse procedure not only can effectively locate the promising areas in the solution space for a global minimum but also avoids its wandering near the global minimum in the final stage of search. In addition, our approach differs from others in the model parameterization: Instead of subdividing the model into a large number of thin layers, we invert for thickness, velocities and densities and their vertical gradients of four layers, sediments, upper-crust, lower-crust and upper mantle. The proposed inverse procedure is applied to non-linear inversion of fundamental mode Rayleigh wave group dispersion curves for shear and compressional wave velocities. At first, to determine the efficiency and stability of the SCE method, two noise-free and two noisy synthetic data sets are inverted. Then real data for Makran region in SE Iran are inverted to examine the usage and robustness of the proposed approach on real surface wave data. In a second step, we applied 3D Gravity Modeling based on surface wave analysis results to obtain the density structure and thickness of each layer. The reason for using both types of data sets, is that gravity anomaly has a bad vertical resolution and surface wave group velocities are good for placing layer limits at depth, but they are not very sensitive to densities. Therefore, using gravity data increases the overall resolution of density distribution. In a final step, we used again the SCE method to invert the fundamental mode Rayleigh wave group dispersion curves based on the gravity results. Gravity results like thicknesses and sediment densities have been used to constrain the limit of search space in the SCE method. Results show a high shear and compressional velocity under the Gulf of Oman which reduce to the North of the Makran region. The Moho depth of the Oman Gulf is about 18-28 km and it increases to 46-48 km under the Taftan-Bazman volcanic-arc. The density image shows an average crustal density with maximum values under the Gulf of Oman decreasing northward to the Makran.

  • 3.
    Abdollahi, Somayeh
    et al.
    Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Zeyen, Hermann
    Univ Paris Saclay, Univ Paris Sud, CNRS, GEOPS, F-91405 Orsay, France.
    Ardestani, Vahid Ebrahimzadeh
    Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    3D joint inversion of gravity data and Rayleigh wave group velocities to resolve shear-wave velocity and density structure in the Makran subduction zone, south-east Iran2019In: Journal of Asian Earth Sciences, ISSN 1367-9120, E-ISSN 1878-5786, Vol. 173, p. 275-290Article in journal (Refereed)
    Abstract [en]

    In this study, we developed a method to invert jointly Rayleigh wave group velocities and gravity anomalies for velocity and density structure of the lithosphere. We applied the method to the Makran accretionary prism, SE Iran. The reason for using different data sets is that each of these data sets is sensitive to different parameters. Surface wave group velocities are sensitive mainly to shear wave velocity distribution in depth but do not well resolve density variations. Therefore, joint inversion with gravity data increases the resolution of density distribution. Our approach differs from others mainly in the model parameterization: Instead of subdividing the model into a large number of thin layers, we invert for the properties of only four layers: thickness, P- and S-wave velocities and densities and their vertical gradients in sediments, upper-crust, lower-crust and upper mantle. The method is applied first to synthetic models in order to demonstrate its usefulness. We then applied the method to real data to investigate the lithosphere structure beneath the Makran. The resulting model shows that Moho depth increases from Oman Sea (18-33 km) and Makran fore-arc (33-37 km) to the volcanic-arc (44-46 km). The crustal density is high in the Oman Sea as should be expected for the oceanic crust. We also find a high-velocity anomaly in the upper mantle under the Oman Sea corresponding to the subducting slab. The crust under the fore-arc, volcanic-arc and back-arc settings of Makran subduction zone is characterized by low-velocity zones.

  • 4.
    Amini, Samar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Raeesi, Mohammad
    SeisAnalysis AS, Bergen, Norway.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Zarifi, Zoya
    Univ Western Ontario, Dept Earth Sci, London, ON, Canada.
    Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet2018In: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 22, no 4, p. 815-831Article in journal (Refereed)
    Abstract [en]

    An intraplate earthquake doublet, with 11-min delay between the events, devastated the city of Varzeghan in northwestern Iran on August 11, 2012. The first Mw 6.5 strike-slip earthquake, which occurred after more than 200 years of low seismicity, was followed by an Mw 6.4 oblique thrust event at an epicentral separation of about 6 km. While the first event can be associated with a distinct surface rupture, the absence of a surface fault trace and no clear aftershock signature makes it challenging to identify the fault plane of the second event. We use teleseismic body wave inversion to deduce the slip distribution in the first event. Using both P and SH waves stabilize the inversion and we further constrain the result with the surface rupture extent and the aftershock distribution. The obtained slip pattern shows two distinct slip patches with dissimilar slip directions where aftershocks avoid high-slip areas. Using the estimated slip for the first event, we calculate the induced Coulomb stress change on the nodal planes of the second event and find a preference for higher Coulomb stress on the N-S nodal plane. Assuming a simple slip model for the second event, we estimate the combined Coulomb stress changes from the two events on the focal planes of the largest aftershocks. We find that 90% of the aftershocks show increased Coulomb stress on one of their nodal planes when the N-S plane of the second event is assumed to be the correct fault plane.

  • 5.
    Amini, Samar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Roberts, Roland G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tomographic upper-mantle velocity structure beneath the Iranian Plateau2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 554-557, p. 42-49Article in journal (Refereed)
    Abstract [en]

    The Iranian plateau is one of the most structurally complex and tectonically inhomogeneous regions in the world. In this study, we analyze Pn arrival-times from regional seismicity in order to resolve lateral velocity variations within the uppermost-mantle under the Iranian Plateau. More than 48,000 Pn first arrival times selected from the EHB catalog were used with epicentral distances of 200 to 1600 km. We used regularized isotropic and anisotropic damped least-squares inversion to image lateral velocity variations in the upper mantle. Our velocity model, with high lateral resolution, shows positive anomalies in the Zagros mountain belt with a distinct transition approximately along the Main Zagros Thrust to the lower mantle velocity zone of Central Iran. Anomalously low velocities are observed predominantly beneath NW Iran and eastern Turkey, suggesting a zone of relatively weak mantle. Low velocity region under the Damavand volcano reveals the hot upper mantle beneath the central Alborz mountains.

  • 6.
    Basir, Hadi Mahdavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran.
    Javaherian, Abdolrahim
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran;Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Firouz-Abadi, Roohollah Dehghani
    Sharif Univ Technol, Dept Aerosp Engn, Tehran 1136511155, Iran.
    Gholamy, Shaban Ali
    Natl Iranian Oil Co, Explorat Directorate, Dept Geophys, Tehran 1994814695, Iran.
    Acoustic wave propagation simulation by reduced order modelling2018In: Exploration Geophysics, ISSN 0812-3985, E-ISSN 1834-7533, Vol. 49, no 3, p. 386-397Article in journal (Refereed)
    Abstract [en]

    Wave propagation simulation, as an essential part of many algorithms in seismic exploration, is associated with high computational cost. Reduced order modelling(ROM) is a known technique in many different applications that can reduce the computational cost of simulation by employing an approximation of the model parameters. ROM can be carried out using different algorithms. The method proposed in this work is based on using the most important mode shapes of the model, which can be computed by an efficient numerical method. The numerical accuracy and computational performance of the proposed method were investigated over a simple synthetic velocity model and a portion of the SEG/EAGE velocity model. Different boundary conditions were discussed, and among them the random boundary condition had higher performance for applications like reverse time migration (RTM). The capability of the proposed method for RTM was evaluated and confirmed by the synthetic velocity model of SEG/EAGE. The results showed that the proposed ROM method, compared with the conventional finite element method (FEM), can decrease the computational cost of wave propagation modelling for applications with many simulations like the reverse time migration. Depending on the number of simulations, the proposed method can increase the computational efficiency by several orders of magnitudes.

  • 7.
    Basir, Hadi Mahdavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran.
    Javaherian, Abdolrahim
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran;Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Firouz-Abadi, Roohollah Dehghani
    Sharif Univ Technol, Dept Aerosp Engn, Tehran 1136511155, Iran.
    Gholamy, Shaban Ali
    Natl Iranian Oil Co, Dept Geophys, Explorat Directorate, Tehran 1994814695, Iran.
    Modified imaging condition for reverse time migration based on reduction of modelling time2018In: Exploration Geophysics, ISSN 0812-3985, E-ISSN 1834-7533, Vol. 49, no 4, p. 494-505Article in journal (Refereed)
    Abstract [en]

    Reverse time migration (RTM) is considered as a high-end imaging algorithm due to its ability to image geologically complex environments. However, this algorithm suffers from very high computational costs and low-frequency artefacts. The former drawback is the result of the intensive computations and huge memory allocation involved in RTM. Wave propagation modelling, as a kernel of RTM, demands intensive computations, and conventional imaging conditions are associated with huge memory allocation. In this paper, a modification of imaging condition is proposed that improves the efficiency of RTM as a reduction of computational cost, memory (RAM) allocation and low-frequency artefacts. The proposed imaging condition is similar to the conventional imaging condition but with the reduction of modelling time to near half the maximum time of recording. As the main idea of the proposed imaging condition, the impact of wave propagation modelling time is investigated on the quality of RTM and illumination of reflectors. The performance of the proposed method is considered using two synthetic models (SEG/EAGE and BP) and a real dataset from an Iranian oilfield in the south of Iran. Results showed that the new imaging condition can properly image the reflectors and enhance the efficiency of RTM. By using the proposed imaging condition, we achieved similar to 25% increase in CPU performance and 50% decrease in the memory allocation. Despite the improvement of the performance, results showed that the proposed imaging condition had no significant effect on the illumination.

  • 8.
    Basir, Hadi Mandavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran, Iran.
    Javaherian, Abdolrahim
    Amirkabir Univ Technol, Dept Petr Engn, Tehran, Iran;Univ Tehran, Inst Geophys, Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran, Iran.
    Firouz-Abadi, Roohollah Dehghani
    Sharif Univ Technol, Dept Aerosp Engn, Tehran, Iran.
    Gholamy, Shaban Ali
    Natl Iranian Oil Co, Explorat Directorate, Dept Geophys, Tehran, Iran.
    Reverse time migration by Krylov subspace reduced order modeling2018In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 151, p. 298-308Article in journal (Refereed)
    Abstract [en]

    Imaging is a key step in seismic data processing. To date, a myriad of advanced pre-stack depth migration approaches have been developed; however, reverse time migration (RTM) is still considered as the high-end imaging algorithm. The main limitations associated with the performance cost of reverse time migration are the intensive computation of the forward and backward simulations, time consumption, and memory allocation related to imaging condition. Based on the reduced order modeling, we proposed an algorithm, which can be adapted to all the aforementioned factors. Our proposed method benefit from Krylov subspaces method to compute certain mode shapes of the velocity model computed by as an orthogonal base of reduced order modeling. Reverse time migration by reduced order modeling is helpful concerning the highly parallel computation and strongly reduces the memory requirement of reverse time migration. The synthetic model results showed that suggested method can decrease the computational costs of reverse time migration by several orders of magnitudes, compared with reverse time migration by finite element method.

  • 9.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Plomerova, Jaroslova
    GFU, Prague.
    Vecsey, Ludek
    GFU, Prague.
    Babuska, Vladislav
    GFU, Prague.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Effects of seismic anisotropy on P-velocity tomography of the Baltic Shield2012In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 188, no 2, p. 600-612Article in journal (Refereed)
    Abstract [en]

    We investigate possible effects of neglecting seismic anisotropy on standard isotropic P-velocity tomographic images of the upper mantle beneath the Baltic shield. Isotropic inversions of teleseismic P- and S-wave traveltimes exhibit alternating high- and low-velocity heterogeneities down to depths of over 400 km. Differences in tomographic inversions of SV- and SH-wave traveltimes are distinct down to depths of about 200 km and are associated with anisotropy of the lithospheric mantle. Anisotropic structures of the upper mantle affect both the P and S traveltimes, shear-wave splitting as well as the P polarization directions. Joint inversion for isotropic and anisotropic velocity perturbations is not feasible due to the limited 3-D ray coverage of available data. Therefore, we correct the input traveltimes for anisotropic contributions derived from independent analyses and then perform standard isotropic inversions. These corrections are derived either directly from directional deviations of P-wave propagation or are calculated in anisotropic models retrieved by joint inversions of body-wave anisotropic parameters (P-residual spheres and shear-wave splitting). These anisotropic models are also used to fit backazimuth variations of P-wave polarization directions. General features of tomographic images calculated from the original and the anisotropy-corrected data are similar. Amplitudes of the velocity perturbations decrease below similar to 200 km depth, that is in the sub-lithospheric mantle. In general, large-scale anisotropy related to the fabrics of the continental mantle lithosphere can contaminate tomographic images in some parts of models and should not be ignored.

  • 10.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hieronymus, Christoph F.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    S and P velocity heterogeneities within the upper mantle below the Baltic Shield2008In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 462, no 1-4, p. 109-124Article in journal (Refereed)
    Abstract [en]

    Upper mantle structure beneath the Baltic (Fennoscandian) Shield is investigated using non-linear tomographic inversion of relative arrival-time residuals. 52 selected teleseismic earthquakes recorded by 45 broadband stations of the Swedish National Seismological Network (SNSN) provide 1532 good quality S-wave relative arrival times. SV and SH arrival-time residuals were initially analyzed independently, providing two separate models. These reveal several consistent major features, many of which are also consistent with P-wave results. Lateral velocity variations of ± 3–4% are observed to depths of at least 470 km. The correlation between the SH and SV models is investigated and shows a pattern of minor but significant differences down to around 150–200 km depth, below which the models are essentially similar. Direct cell by cell comparison of the model velocities reveals a similar pattern, with velocity differences between the models of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially attributed to noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. One of the significant and sharp discrepancies between the S models coincides with a presumed boundary between Archean and Proterozic domains, suggesting different anisotropic characteristics in the two regions.

  • 11. Gregersen, S.
    et al.
    Voss, P.
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Grad, M.
    Roberts, Roland G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Physical differences in the deep lithosphere of northern and central Europe2006In: Geological Society of London, Memoirs, Vol. 32, p. 313-322Article in journal (Refereed)
    Abstract [en]

    A number of large-scale integrated studies, including the TOR and POLONAISE'97 projects, with an emphasis on seismic methods, have been used to elucidate the southwestern boundary (suture zone) between the East European Craton and the Phanerozoic terranes of Western Europe. Results indicate that a thick slab of mantle lithosphere below the craton thins southwestwards beneath the Trans-European Suture Zone and is not seen south of the Variscan front. The thinning is not gradual, but is interrupted by at least two abrupt deep boundaries, the most significant of which corresponds to the surface position of the Tornquist Zone, a major fault. The present geometry of the lithosphere is the result of modification of the margin of the Neoproterozoic continent Baltica by Phanerozoic processes, including the development of the Tornquist Zone and the stretching of the lithosphere in a broad central block SW of this zone. Seismic results and their interpretations from the TOR tomographic project are presented and compared with results from the POLONAISE'97 controlled source project to the SE. Both investigations have shown high-angle, non-symmetrical features extending deep into the mantle.

  • 12.
    Gregersen, S.
    et al.
    GEUS,Denmark.
    Voss, P.
    GEUS,Denmark.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Grad, M.
    University of Warsaw,Poland.
    Roberts, Roland G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Physical differences in the deep lithosphere of Northern and Central Europe2006In: European Lithosphere Dynamics / [ed] Gee, D.G. and Stephenson, R.a., Geological Society of London , 2006, 32, p. 313-322Chapter in book (Other academic)
    Abstract [en]

    A number of large-scale integrated studies, including the TOR and POLONAISE’97 projects, with an emphasis on seismicmethods, have been used to elucidate the southwestern boundary (suture zone) between the East European Craton and the Phanerozoicterranes of Western Europe. Results indicate that a thick slab of mantle lithosphere below the craton thins southwestwards beneath theTrans-European Suture Zone and is not seen south of the Variscan front. The thinning is not gradual, but is interrupted by at least twoabrupt deep boundaries, the most significant of which corresponds to the surface position of the Tornquist Zone, a major fault. Thepresent geometry of the lithosphere is the result of modification of the margin of the Neoproterozoic continent Baltica by Phanerozoicprocesses, including the development of the Tornquist Zone and the stretching of the lithosphere in a broad central block SW of thiszone. Seismic results and their interpretations from the TOR tomographic project are presented and compared with results from thePOLONAISE’97 controlled source project to the SE. Both investigations have shown high-angle, non-symmetrical features extendingdeep into the mantle.

  • 13. Heidari, Reza
    et al.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ghayamghamian, Mohammad Reza
    Magnitude-scaling relations using period parameters tau(c) and tau(max)(p), for Tehran region, Iran2013In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 192, no 1, p. 275-284Article in journal (Refereed)
    Abstract [en]

    In this study, the first step towards establishing an onsite earthquake early warning system (EWS) in the Tehran region is presented. The system uses the period parameters tau(max)(p) and tau(c) from the first 3 s of the vertical and horizontal components of a P wave, separately and combined. Various regression relations between the magnitude and period parameters were determined for different seismic networks operating in the study area. The data set used in this study contains small ground motions including 194 events with magnitudes between M-L 2.5 and 4.6 located within approximately 80 km from the epicentre in the Tehran region. The SDs of the magnitude-scaling relations for all the component categories (vertical, horizontal and total components) based on the tau(max)(p) and tau(c) approaches were estimated to be on the order of +/- 1.0 and +/- 1.1 unit of magnitude, respectively. These relations were determined from the small magnitude range of the velocity records (M-L 2.5-4.6) as input seismograms. Additional tests were conducted to verify the reliability and robustness of the determined magnitude-scaling relations using acceleration records from the 2002 June 22, M-L 6.5 Changureh-Avaj earthquake; 2004 May 28, M-L 6.1 Firoozabad-Koojour earthquake; 2009 October 17, M-L 3.9 Shahre-Rey earthquake and 2011 February 20, M-L 4.1 Sharif-Abad earthquake; the first two events (Changureh-Avaj and Firoozabad-Koojour) occurred outside the study area. Among the various regression scaling relations obtained, the estimated magnitude based on the tau(max)(p) approach using the vertical components yielded the most stable and reliable results of 6.4 (+/- 0.4), 5.9 (+/- 0.4), 3.3 (+/- 0.5) and 3.8 (+/- 0.3) for the Changureh-Avaj, Firoozabad-Koojour, Shahre-Rey and Sharif-Abad earthquakes, respectively. The magnitudes estimated using the tau(c) method exhibited more scatter with higher SDs than those using the vertical components using the tau(max)(p) approach. Our results also indicate that using the horizontal components produces larger SDs, which may be attributed to the larger site effects; however, the horizontal components can be used as auxiliary available data to provide more constrained information for a multilevels pilot alarm system and to reduce the number of missed or false alarms. The main uncertainties in the proposed magnitude-scaling relations result from the absence of any large earthquakes and poor station distributions in the study area. However, the results presented in this study can be used as a pilot onsite earthquake EWS in the Tehran region.

  • 14.
    Hieronymus, Christoph F.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    A dynamical model for generating sharp seismic velocity contrasts underneath continents: Application to the Sorgenfrei-Tornquist Zone2007In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 262, no 1-2, p. 77-91Article in journal (Refereed)
    Abstract [en]

    New seismic velocity models based on teleseismic traveltime tomography show a sharp lithospheric boundary at the Sorgenfrei–Tornquist Zone (STZ) between 100 and 250 km depth with P-waves about 4% faster and S-waves 6% faster within the cratonic lithosphere to the north. Experiments and thermodynamic calculations indicate that seismic velocity differences in the shallow mantle down to the transition zone must be mostly of thermal origin as typical mantle rocks are characterized by similar velocities based on composition alone. We propose a dynamical model of convection in the upper mantle that is consistent with rheological data and that satisfies the seismic observations by maintaining an abrupt lateral temperature contrast over hundreds of Myrs. A step-like increase in lithospheric thickness from 100 to 250 km is assumed to have formed in a Triassic rifting event at the STZ (around 220 Ma) and is subsequently exposed to active convection below. A lithosphere that is distinct from the mantle in terms of temperature and composition remains stable against convective erosion. Heat advection to different depth beneath the thin and the thick lithosphere leads to a maximum horizontal contrast of 500 °C at 150 km depth over a lateral transition distance of 100 km, sufficient to generate 5% and 8% in maximum P- and S-wave velocity perturbation, respectively. A purely conductive model under the same conditions yields only Δvp ≈ 1% and Δvs ≈ 2%, while a lithospheric evolution simulation without a compositional effect on the rheology leads to significant thermo-mechanical erosion of the lithosphere giving Δvp ≈ 2% and Δvs ≈ 4%.

  • 15.
    Karkooti, Ehsan
    et al.
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Pakzad, Mehrdad
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Investigating the role of source mechanism, surface topography, and attenuation on the observed PGA pattern in May 28, 2004, Mw 6.2 Baladeh earthquake (Iran)2016In: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 20, no 2, p. 495-510Article in journal (Refereed)
    Abstract [en]

    In this paper, we use seismic waveform simulation to investigate the influence of source mechanism complexity, surface topography, and quality factor on the observed peak ground motions in May 28, 2004, moment magnitude (Mw) 6.2 Baladeh earthquake. The observed peak ground acceleration (PGA) pattern in this event, which is the biggest earthquake to hit the Central Alborz Mountains of Iran in modern instrumental era, is irregular in some respects. First, the observed PGA contours are elongated toward north-west and, second, the maximum observed PGA value of 1049 cm/s(2) on the horizontal component of Hasan Keyf station 50 km away from the epicenter is quite high and irregular for an earthquake of this magnitude, at such long distance. In this study, we employ the spectral element method, implemented in SPECFEM3D software package to simulate the 3D wave propagation from several source models in the area. Our results suggest directivity effect is the main cause of the anomalous observations in this earthquake and could account for the elongation of PGA contours and also the anomalous maximum PGA value observed at Hasan Keyf strong motion station. We show that the surface topography has minor effect on the observed peak ground acceleration and the resulting PGA maps. Also by finding the bounds of seismic quality factor effect on the peak ground acceleration values, we show that this factor could not account for the elongation of iso-acceleration contours in the north-west direction.

  • 16. Kind, R.
    et al.
    Sodoudi, F.
    Yuan, X.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Gee, David G.
    Eken, T.
    Bianchi, M.
    Tilmann, F.
    Balling, N.
    Jacobsen, B. H.
    Kumar, P.
    Geissler, W. H.
    Scandinavia: A former Tibet?2013In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 14, no 10, p. 4479-4487Article in journal (Refereed)
    Abstract [en]

    The Himalaya and the Tibetan Plateau are uplifted by the ongoing northward underthrusting of the Indian continental lithosphere below Tibet resulting in lithospheric stacking. The layered structure of the Tibetan upper mantle is imaged by seismic methods, most detailed with the receiver function method. Tibet is considered as a place where the development of a future craton is currently under way. Here we study the upper mantle from Germany to northern Sweden with seismic S receiver functions and compare the structure below Scandinavia with that below Tibet. Below Proterozoic Scandinavia, we found two low-velocity zones on top of each other, separated by a high-velocity zone. The top of the upper low-velocity zone at about 100 km depth extends from Germany to Archaean northern Sweden. It agrees with the lithosphere-asthenosphere boundary (LAB) below Germany and Denmark. Below Sweden it is known as the 8 degrees discontinuity, or as a mid-lithospheric discontinuity (MLD), similar to observations in North America. Seismic tomography places the LAB near 200 km in Scandinavia, which is close to the top of our deeper low-velocity zone. We also observed the bottom of the asthenosphere (the Lehmann discontinuity) deepening from 180 km in Germany to 260 km below Sweden. Remnants of old subduction in the upper about 100 km below Scandinavia and Finland are known from controlled source seismic experiments and local earthquake studies. Recent tomographic studies indicate delamination of the lithosphere below southern Scandinavia and northern Germany. We are suggesting that the large-scale layered structure in the Scandinavian upper mantle may be caused by processes similar to the ongoing lithospheric stacking in Tibet.

  • 17.
    Maleki, V.
    et al.
    University of Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hatami, M.R.
    University of Tehran, Iran.
    Pakzad, M.
    University of Tehran, Iran.
    Lomax, A.
    ALomax Scientific, Mouans-Sartoux, France.
    Earthquake relocation in the Central Alborz region of Iran using a non-linear probabilistic method2013In: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 17, no 2, p. 615-628Article in journal (Refereed)
    Abstract [en]

    In this study, we calculate accurate absolutelocations for nearly 3,000 shallow earthquakes(≤20 km depth) that occurred from 1996 to 2010 inthe Central Alborz region of northern Iran using a nonlinearprobabilistic relocation algorithm on a localscale. We aim to produce a consistent dataset with arealistic assessment of location errors using probabilistichypocenter probability density functions. Ourresults indicate significant improvement in hypocenterlocations and far less scattering than in the routineearthquake catalog. According to our results, 816earthquakes have horizontal uncertainties in the 0.5–3.0 km range, and 981 earthquakes are relocated withfocal-depth errors less than 3.0 km, even with a suboptimalnetwork geometry. Earthquake relocated aretightly clustered in the eastern Tehran region and aremainly associated with active faults in the study area(the Mosha and Garmsar faults). Strong historicalearthquakes have occurred along the Mosha andGarmsar faults, and the relocated earthquakes alongthese faults show clear north-dipping structures andalign along east–west lineations, consistent with thepredominant trend of faults within the study region.After event relocation, all seismicity lies in the upper20 km of the crust, and no deep seismicity (>20 kmdepth) has been observed. In many circumstances, theseismicity at depth does not correlate with surfacefaulting, suggesting that the faulting at depth doesnot directly offset overlying sediments.

  • 18. Mostafanejad, Akram
    et al.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mottaghi, Ali A.
    3-D velocity structure of Damavand volcano, Iran, from local earthquake tomography2011In: Journal of Asian Earth Sciences, ISSN 1367-9120, E-ISSN 1878-5786, Vol. 42, no 6, p. 1091-1096Article in journal (Refereed)
    Abstract [en]

    Damavand volcano is a large intraplate Quaternary composite cone overlying the active fold and thrust belt of the Central Alborz Mountains in northern Iran. In this study, we present the first 3-D P-wave velocity model of the upper crust for the Central Alborz region using local earthquake data provided by the Iranian Seismic Telemetry Network. The final P-wave velocity model reveals several high and low velocity anomalies in the upper 30 km of the crust. A low velocity zone parallel to the main faulting system is imaged at a depth of 15 km. A relatively high velocity body to the north of the Damavand summit down to a depth of 20 km is resolved, which may represent the elderly crystallized magma chamber. Right below the Damavand cone, a low velocity area to the depth of 7 km can be interpreted as a shallow magma chamber.

  • 19.
    Nazeri, Sahar
    et al.
    Univ Tehran, Inst Geophys, North Kargar St, Tehran, Iran;Univ Naples Federico II, Complesso Univ Monte S Angelo, Dept Phys, RISSC Lab, I-80126 Naples, Italy.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, North Kargar St, Tehran, Iran.
    Rapid Estimation of the Epicentral Distance in the Earthquake Early Warning System around the Tehran Region, Iran2019In: Seismological Research Letters, ISSN 0895-0695, E-ISSN 1938-2057, Vol. 90, no 5, p. 1916-1922Article in journal (Refereed)
    Abstract [en]

    The estimation of epicentral distance is a critical step in earthquake early warning systems (EEWSs) that is necessary to characterize the level of expected ground shaking. In this study, two rapid methodologies, that is, B-Delta and C-Delta , are evaluated to estimate the epicentral distance for use in the EEWSs around the Tehran region. Traditionally, the B and C coefficients are computed using acceleration records, however, in this study, we utilize both acceleration and velocity waveforms for obtaining a suitable B-Delta and C-Delta relationships for the Tehran region. In comparison with observations from Japan, our measurements fall within the range of scatter. However, our results show a lower trend, which can strongly depend on the few numbers of events and range of magnitude (small-to-moderate) of earthquakes used in the current research. To improve our result, we include some large earthquakes from Iran, Italy, and Japan with magnitude larger than 5.9. Although the optimal trend is finally obtained by fitting a line to the distance-averaged points, we conclude that the same trend and relationship as Japan can be used in Tehran early warning system. We also found that B and C parameters are strongly compatible to each other. As time windows of 3.0 and 0.5 s after the P onset are chosen respectively to compute the B and C values, so by selecting the C parameter as a proxy of B parameter to estimate the epicentral distance, we may save significant time in order of about 2.5 s in any earthquake early warning applications.

  • 20.
    Nazeri, Sahar
    et al.
    Univ Tehran, Inst Geophys, North Kargar St, Tehran, Iran..
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, North Kargar St, Tehran, Iran..
    Colombelli, Simona
    Univ Naples Federico II, RISSC Lab, Dept Phys, Complesso Univ Monte S Angelo, I-80126 Naples, Italy..
    Elia, Luca
    AMRA Scarl, Via Nuova Agnano 11, I-80125 Naples, Italy.;Univ Naples Federico II, RISSC Lab, Dept Phys, Complesso Univ Monte S Angelo, I-80126 Naples, Italy..
    Zollo, Aldo
    Univ Naples Federico II, RISSC Lab, Dept Phys, Complesso Univ Monte S Angelo, I-80126 Naples, Italy..
    Magnitude Estimation Based on Integrated Amplitude and Frequency Content of the Initial P Wave in Earthquake Early Warning Applied to Tehran, Iran2017In: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 107, no 3, p. 1432-1438Article in journal (Refereed)
    Abstract [en]

    To optimize magnitude estimation for the earthquake early warning system around the Tehran region, different amplitude-and frequency-based parameters, that is, predominant period (tau(max)(p)), characteristic period (tau(c)), log-average period (tau(log)), and peak displacement (P-d) were analyzed in this article. All parameters were calculated directly from seismic records, with an epicentral distance less than 150 km, and within the initial 3 s of the P waves. The analysis of earthquakes in the 2.4 < M-L< 4.9 magnitude range verified that the result of tau(max)(p) showed a consistent trend as compared with the global observations, and provided a robust estimate of magnitude for the dataset used in this research. In comparison with worldwide observations, the calculated P-d and tau(c) were underestimated, and there was no scaling relationship with the tau(log) parameter. When combined with the global observations from Japan, Taiwan, and Italy, the results of P-d and tc for the Tehran region produced optimized results.

  • 21.
    Rashidi, Amin
    et al.
    Univ Tehran, Inst Geophys, Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran, Iran.
    Dutykh, Denys
    Univ Grenoble Alpes, Univ Savoie Mt Blanc, CNRS, LAMA, F-73000 Chambery, France;Univ Savoie Mt Blanc, LAMA UMR CNRS 5127, Campus Sci, F-73376 Le Bourget Du Lac, France.
    Khah, Nasser Keshavarz Faraj
    Res Inst Petr Ind, Tehran, Iran.
    Evaluation of tsunami wave energy generated by earthquakes in the Makran subduction zone2018In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 165, p. 131-139Article in journal (Refereed)
    Abstract [en]

    The MAKRAN subduction zone, an approximate 1000 km section of the EURASIAN-ARABIAN plate, is located offshore of SOUTHERN IRAN and PAKISTAN. In 1945, the MAKRAN subduction zone (MSZ) generated a tsunamigenic earthquake with a magnitude of M-w 8.1. The region has also experienced large historical earthquakes but the data regarding these events are poorly documented. Therefore, the need to investigate tsunamis in MAKRAN must be taken into serious consideration. Using hydrodynamic numerical simulation, we evaluate the tsunami wave energy generated by bottom motion for a tsunamigenic source model distributed along the full length of the MAKRAN subduction zone. The whole rupture of the plate boundary is divided into 20 segments with width of the order of 200 km and a co-seismic slip of 10 m but with various lengths. Exchanges between kinetic and potential components of tsunami wave energy are shown. The total tsunami wave energy displays only 0.33 % of the seismic energy released from the earthquake source. As a result, for every increase in magnitude by one unit, the associated tsunami wave energy becomes about 10(3) times greater.

  • 22.
    Rashidi, Amin
    et al.
    Univ Tehran, Inst Geophys, Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran, Iran.
    Farajkhah, Nasser Keshavarz
    RIPI, Tehran, Iran.
    Tsunami Simulations in the Western Makran Using Hypothetical Heterogeneous Source Models from World's Great Earthquakes2018In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 175, no 4, p. 1325-1340Article in journal (Refereed)
    Abstract [en]

    The western segment of Makran subduction zone is characterized with almost no major seismicity and no large earthquake for several centuries. A possible episode for this behavior is that this segment is currently locked accumulating energy to generate possible great future earthquakes. Taking into account this assumption, a hypothetical rupture area is considered in the western Makran to set different tsunamigenic scenarios. Slip distribution models of four recent tsunamigenic earthquakes, i.e. 2015 Chile M-w 8.3, 2011 Tohoku-Oki M-w 9.0 (using two different scenarios) and 2006 Kuril Islands M-w 8.3, are scaled into the rupture area in the western Makran zone. The numerical modeling is performed to evaluate near-field and far-field tsunami hazards. Heterogeneity in slip distribution results in higher tsunami amplitudes. However, its effect reduces from local tsunamis to regional and distant tsunamis. Among all considered scenarios for the western Makran, only a similar tsunamigenic earthquake to the 2011 Tohoku-Oki event can re-produce a significant far-field tsunami and is considered as the worst case scenario. The potential of a tsunamigenic source is dominated by the degree of slip heterogeneity and the location of greatest slip on the rupture area. For the scenarios with similar slip patterns, the mean slip controls their relative power. Our conclusions also indicate that along the entire Makran coasts, the southeastern coast of Iran is the most vulnerable area subjected to tsunami hazard.

  • 23.
    Rezaeifar, M.
    et al.
    Swiss Fed Inst Technol, Inst Geophys, Dept Geophys, Sonneggstr 5, CH-8092 Zurich, Switzerland.;Grad Univ Adv Technol, Dept Geol, Kerman, Iran..
    Kissling, E.
    Swiss Fed Inst Technol, Inst Geophys, Dept Geophys, Sonneggstr 5, CH-8092 Zurich, Switzerland..
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran, Iran..
    Shahpasand-Zadeh, M.
    Grad Univ Adv Technol, Dept Geol, Kerman, Iran..
    3D crustal structure of the northwest Alborz region (Iran) from local earthquake tomography2016In: Swiss Journal of Geosciences, ISSN 1661-8726, E-ISSN 1661-8734, Vol. 109, no 3, p. 389-400Article in journal (Refereed)
    Abstract [en]

    We performed a 3D seismic tomography study of the northwest Alborz region in Iran, by inversion of P-wave arrival times of nearly 250 local earthquakes recorded at 13 permanent stations between 2006 and 2010. We applied the simultaneous inversion code SIMULPS14 carefully tuned to data set by choice of optimal regularization parameters. Resolution tests with synthetic data show that the inversion results are well constrained around the North Tabriz Fault (NTF) from 3 to 16 km depth. In this depth range, our results show a series of anomalies with relatively high and low velocity, reflecting the heterogeneous geology of northwest Alborz and generally correlating well with local changes of rock types at the surface across this section of the NTF. The boundary surface between the distinct velocity anomalies is generally consistent with the NTF strike. The high and low velocity anomalies at 5-14 km depth parallel to the surface expression of the NTF are interpreted as basaltic volcanic rocks in the south and Mesozoic sedimentary and basement rocks in the north. In addition, cross sections show a significant change in dip of the NTF in the southeastern part, from nearly vertical in the NW to about 60A degrees dip toward SE.

  • 24. Shirzad, Taghi
    et al.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shallow crustal radial anisotropy beneath the Tehran basin of Iran from seismic ambient noise tomography2014In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 231, p. 16-29Article in journal (Refereed)
    Abstract [en]

    We studied the shear wave velocity structure and radial anisotropy beneath the Tehran basin by analyzing the Rayleigh wave and Love wave empirical Green's functions obtained from cross-correlation of seismic ambient noise. Approximately 199 inter-station Rayleigh and Love wave empirical Green's functions with sufficient signal-to-noise ratios extracted from 30 stations with various sensor types were used for phase velocity dispersion analysis of periods ranging from I to 7 s using an image transformation analysis technique. Dispersion curves extracted from the phase velocity maps were inverted based on non-linear damped least squares inversion method to obtain a quasi-3D model of crustal shear wave velocities. The data used in this study provide an unprecedented opportunity to resolve the spatial distribution of radial anisotropy within the uppermost crust beneath the Tehran basin. The quasi-3D shear wave velocity model obtained in this analysis delineates several distinct low- and high-velocity zones that are generally separated by geological boundaries. High-shear-velocity zones are located primarily around the mountain ranges and extend to depths of 2.0 km, while the low-shear-velocity zone is located near regions with sedimentary layers. In the shallow subsurface, our results indicate strong radial anisotropy with negative magnitude (Vsv > VsH) primarily associated with thick sedimentary deposits, reflecting vertical alignment of cracks. With increasing depth, the magnitude of the radial anisotropy shifts from predominantly negative (less than - 10%) to predominantly positive (greater than 5%). Our results show a distinct change in radial anisotropy between the uppermost sedimentary layer and the bedrock.

  • 25. Shirzad, Taghi
    et al.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shallow crustal structures of the Tehran basin in Iran resolved by ambient noise tomography2014In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 196, no 2, p. 1162-1176Article in journal (Refereed)
    Abstract [en]

    In this study, we present an application of the ambient noise tomography (ANT) to study the near-surface geological structures of the metropolitan Tehran/Iran region. Short-period fundamental mode Rayleigh wave Green's functions were estimated using cross-correlations of the vertical component of the ambient noise from 2009 October to 2011 May using a variety of seismic sensors, for example, accelerometers and seismometers, deployed in the Tehran area. Standard common low frequency processing procedures were applied to the cross-correlations, and shorter time-windows comprising 10-min segments were used in the processing step to enhance the time resolution of the signal in the frequency range of interest (1-10 s). Stacking was also conducted using the rms of the estimated empirical Green's functions. Our results demonstrate that ambient seismic noise tomography is a viable technique at periods of 1-10 s in length, even when different sensor types are present. Analysis of the empirical Green's functions indicates that the dominant sources of ambient seismic noise originated from the same origin, and no significant seasonal or spatial variations in the ambient noise sources were observed. Multiple-filter analysis was used to extract the group velocities from the estimated empirical Green's functions, which were then inverted to image the spatially varying dispersion at periods of lengths between 1 and 7 s using tomographic inversion of the traveltimes estimated for each frequency. The resulting group velocity maps show high correlations with known geological and tectonic features of the study region. In general, most of the Tehran basin, with certain exceptions, could be clearly resolved with low group velocities, whereas the mountain ranges were found to be correlated with high group velocities. In the Tehran basin, for 2 and 3 s periods, the low-velocity zone deepens towards the south-southwest, which reflects thicker sediments in the southern part of the basin than in the north. This feature has also been observed in other geological studies. The Vs models also show that bedrock depth varies between 400 and 1400 m from north to south within the Tehran basin. At longer periods main faults are associated with abrupt transitions between regions of high- to low-velocity anomalies. In general, our results indicate that ANT can be a flexible and effective approach for studying near-surface heterogeneity using short-period surface wave data.

  • 26. Shirzad, Taghi
    et al.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Institute of Geophysics, University of Tehran, Tehran, Iran .
    Naghavi, Mojtaba
    Norouzi, Rahim
    Near-surface VS structure by inversion of surface wave estimated from ambient seismic noise2015In: Near Surface Geophysics, ISSN 1569-4445, E-ISSN 1873-0604, Vol. 13, no 5, p. 447-453Article in journal (Refereed)
  • 27. Shirzad, Taghi
    et al.
    Shomali, Zaher-Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Extracting Seismic Body and Rayleigh Waves from the Ambient Seismic Noise Using the rms-Stacking Method2015In: Seismological Research Letters, ISSN 0895-0695, E-ISSN 1938-2057, Vol. 86, no 1, p. 173-180Article in journal (Refereed)
  • 28.
    Shirzad, Taghi
    et al.
    Islamic Azad Univ, Dept Phys, Damavand Branch, Damavand 39715194, Iran..
    Shomali, Zaher-Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Extracting Stable Seismic Core Phases from Ambient Seismic Noise2016In: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 106, no 1, p. 307-312Article in journal (Refereed)
    Abstract [en]

    Ambient seismic-noise correlation is a powerful tool for extracting the seismic core phases that propagate through the interior of the Earth. In this study, we present and refine the root-mean-square-stacking method to extract stable core phases (e.g., PcP, ScS, PcS/ScP, and PKiKP) from within the Central Alborz region, Iran, using empirical Green's functions. Our studies on the extracted core phases using empirical Green's functions indicated that the ambient seismic noise method is independent from global seismicity (M >= 5.5). We also show that, by dividing ambient seismic records into shorter (i.e., 2700 s) and overlapping (70%) time windows, before the cross-correlation procedure, we can improve the quality and stability of the empirical Green's functions generated. Consequently, 73 days (equivalent to 22% of the total time period for the dataset) of nonconsecutive ambient seismic-noise time windows have been used to retrieve core-phase empirical Green's functions in a 5-10 s period band.

  • 29. Shirzad, Taghi
    et al.
    Shomali, Zaher-Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Riahi, Mohammad-Ali
    An Application of Ambient Noise and Earthquake Tomography in the Rigan Area, Southeast of Iran2013In: Seismological Research Letters, ISSN 0895-0695, E-ISSN 1938-2057, Vol. 84, no 6, p. 1014-1020Article in journal (Refereed)
  • 30.
    Shirzad, Taghi
    et al.
    Islamic Azad Univ, Dept Phys, Damavand Branch, Damavand 39715194, Iran..
    Shomali, Zaher-Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Riahi, Mohammad-Ali
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Jarrahi, Maziar
    Pars Petro Zagros Geophys Co PPZG, Tehran, Iran..
    Near surface radial anisotropy in the Rigan area/SE Iran2017In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 694, p. 23-34Article in journal (Refereed)
    Abstract [en]

    By analyzing Rayleigh and Love wave empirical Green's functions extracted from ambient seismic noise and earthquake data, we obtained near surface radial anisotropy structure beneath the hidden part of the Kahurak fault in the Rigan region, in the southeast oilcan. The deduced seismic radial anisotropy within the hidden part of the Kahurak fault can reveal record of shallow crustal deformation caused by the Rigan earthquake (M-W 6.5) occurred on 20 December 2010. Significant radial anisotropy with positive magnitude (V-SH > V-SV) appears in the shallow subsurface of the upper part of the crust. The magnitude of radial anisotropy varies from predominantly positive (V-SH > V-SV) to mostly negative (V-SH < V-SV) values with increasing depth which is correlated with a known sedimentary layer. The sedimentary layer is observed with prominent positive radial anisotropy (V-SH > V-SV). The thickness of the sedimentary layer varies between 1 and 3 km from the south to the north beneath the study area with an average radial anisotropy of about 5%. However, cross-section profiles indicate that negative ahomaly stretches inside a thick sedimentary layer where the aftershocks occurred. Also, the investigation of cross-section profiles reveals that a dipping angle of the hidden part of Kahurak fault is resolved at approximately 85 using the anisotropy pattern. Moreover, the aftershocks generally occurred in the transitional zones where signs of radial anisotropy anomalies change. Our study indicates that the influence of different resolving powers and path coverage density of Rayleigh and Love waves, which can be artificially interpreted as radial anisotropy, have minor effect on calculated radial anisotropy and they are estimated in the range of -2% to +2%.

  • 31.
    Shomali, Zaher Hossein
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shirzad, Taghi
    Crustal structure of Damavand volcano, Iran, from ambient noise and earthquake tomography2015In: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 19, no 1, p. 191-200Article in journal (Refereed)
    Abstract [en]

    We investigated the shear wave velocity structure beneath the Damavand volcano, Iran, using analysis of Rayleigh wave empirical Green's functions obtained from the cross-correlation of 1-year seismic ambient noise and 26 local earthquakes. After the observed phase, velocity dispersion curves were inverted to obtain phase velocity tomographic maps; the synthetic phase velocity dispersion curves were then estimated for each evenly spaced geographic grid point. Estimated synthetic phase velocities were inverted using the nonlinear damped least-squares inversion method to obtain a quasi-3D shear wave velocity for the study area. Analysis of obtained quasi-3D shear wave velocity model reveals the presence of three distinct low or high anomalies in the upper 5 km. A low-velocity layer (V (S) similar to 2.8 km/s) was observed in the upper similar to 2 km of the crust that includes the sedimentary sequence of carbonate, siliciclastic, and volcanic rocks. According to our results, there is an indication of a high-velocity layer (V (S) a parts per thousand yenaEuro parts per thousand 3.0 km/s) at the depth range of 2 to 5 km, which may indicate the presence of dense, cooled magma. There is a clear indication of intrusion of the low-velocity anomaly/body into the higher velocity layer, in the depth range of approximately 3.0 to 4.5 km. The corresponding low-velocity body is interpreted as a hot magma chamber associated with the young eruption of Damavand. The chamber is located southwest of the crater, which stretches from the west to beneath the Damavand cone.

  • 32. Vinnik, Lev
    et al.
    Oreshin, Sergey
    Makeyeva, Larissa
    Peregoudov, Dmitriy
    Kozlovskaya, Elena
    Pedersen, Helle
    Plomerova, Jaroslava
    Achauer, Ulrich
    Kissling, Eduard
    Sanina, Irina
    Jamsen, Teppo
    Silvennoinen, Hanna
    Pequegnat, Catherine
    Hurskainen, Riitta
    Guiguet, Robert
    Hausmann, Helmut
    Jedlicka, Petr
    Aleshin, Igor
    Bourova, Ekaterina
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bruckl, Evald
    Eken, Tuna
    Heikkinen, Pekka
    Houseman, Gregory
    Johnsen, Helge
    Kremenetskaya, Elena
    Komminaho, Kari
    Munzarova, Helena
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ruzek, Bohuslav
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Schweitzer, Johannes
    Shaumyan, Artem
    Vecsey, Ludek
    Volosov, Sergei
    Anisotropic lithosphere under the Fennoscandian shield from P receiver functions and SKS waveforms of the POLENET/LAPNET array2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 628, p. 45-54Article in journal (Refereed)
    Abstract [en]

    Seismic azimuthal anisotropy is the key evidence of the past and present strains in the upper mantle. The standard analysis of shear-wave splitting with the SKS techniques is useful in mapping lateral variations but it is insensitive to depth of anisotropy and to variations of anisotropy with depth. To retrieve the depth localized anisotropy under the Fennoscandian shield, we inverted P-wave receiver functions of the POLENET/LAPNET array in northern Finland jointly with SKS recordings. Shear-wave anisotropy of similar to 2.5% with the fast direction of 40 degrees-60 degrees in a depth range from the Moho to similar to 110 km is a robust result of the inversion. The obtained direction is nearly normal to the azimuth of the maximum horizontal compressional stress in the lithosphere, but a recent origin of this anisotropy is in doubt. This anisotropy may be frozen since the Precambrian, but it shows no clear relation with the trends of the Precambrian tectonics. The upper anisotropic layer accounts for similar to 40% of shear-wave splitting in SKS, and to explain the rest another anisotropic layer is required. The top of the second layer with a practically similar fast direction is found at a depth of 200-240 km. This direction is close to the current APM direction of the lithosphere with implication that the inferred anisotropy may be related with the current plate motion, and the anisotropic layer belongs to the asthenosphere. The bottom of this layer is uncertain, but it is at least 320 km deep. In a depth range from 160 km to 200-240 km the fast anisotropy direction is 110-150 degrees. Origin of this direction is unclear. 

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