Institute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X40320141023New seismic imaging of some tectonic zones in the Iranian PlateauNew seismic imaging of some tectonic zones in the Iranian Plateau1125159410.22059/jesphys.2014.51594FAJournal Article20130729The Iranian Plateau is characterized by diverse tectonic domains, including the continental collisions (e.g. the Zagros and Alborz Mountains) and oceanic plate subduction (e.g. Makransubduction zone). To derive a detailed image of the crust–mantle (Moho) and lithosphere–asthenosphere (LAB) boundaries in some tectonically units of the Iranian Plateau, we used a large number of S receiver functions obtained from teleseismic events recorded at 68 national permanent stations (19 broadband and 49 short period stations). The S receiver functions clearly imaged the base of the crust and lithosphere and their variations within the different tectonic zones of the Iranian Plateau. Our new seismic images show a significant variation of the lithospheric thickness in the different geological features. The most complex structure was detected beneath the Zagros Mountains where the Arabian Plate is believed to underthrust beneath centralIran. We found the thickest crust under the Sanandaj-Sirjan metamorphic zone (SSZ)which proposes the overthrusting of the crust of central Iran into the Zagros crust along the main Zagros thrust (MZT), in agreement with the results of Paul et al., (2010). Furthermore, our results clearly show a shallow LAB at about 80-90 km depth beneath the Alborz, the central domain (CD) and central Iranian micro plate (CIMP) zones. Based on our results, the Arabian LAB, beneath the Zagros fold and thrust belt (ZFTB), SSZ and the Urumieh-Dokhtar magmatic assemblage (UDMA) is 200 km and may contain a dipping structure at depths ranging from 100 beneath the ZFTBto 150 km beneath the SSZ and the UDMA. This dipping structure interpreted as the presence of remnants of the fossil Neo-Tethys subduction. The location of the boundary between the Arabian and central Iranian lithospheres is beneath the UDMA, which is shifted northeastward relative to the surficial expression of the MZT.The Iranian Plateau is characterized by diverse tectonic domains, including the continental collisions (e.g. the Zagros and Alborz Mountains) and oceanic plate subduction (e.g. Makransubduction zone). To derive a detailed image of the crust–mantle (Moho) and lithosphere–asthenosphere (LAB) boundaries in some tectonically units of the Iranian Plateau, we used a large number of S receiver functions obtained from teleseismic events recorded at 68 national permanent stations (19 broadband and 49 short period stations). The S receiver functions clearly imaged the base of the crust and lithosphere and their variations within the different tectonic zones of the Iranian Plateau. Our new seismic images show a significant variation of the lithospheric thickness in the different geological features. The most complex structure was detected beneath the Zagros Mountains where the Arabian Plate is believed to underthrust beneath centralIran. We found the thickest crust under the Sanandaj-Sirjan metamorphic zone (SSZ)which proposes the overthrusting of the crust of central Iran into the Zagros crust along the main Zagros thrust (MZT), in agreement with the results of Paul et al., (2010). Furthermore, our results clearly show a shallow LAB at about 80-90 km depth beneath the Alborz, the central domain (CD) and central Iranian micro plate (CIMP) zones. Based on our results, the Arabian LAB, beneath the Zagros fold and thrust belt (ZFTB), SSZ and the Urumieh-Dokhtar magmatic assemblage (UDMA) is 200 km and may contain a dipping structure at depths ranging from 100 beneath the ZFTBto 150 km beneath the SSZ and the UDMA. This dipping structure interpreted as the presence of remnants of the fossil Neo-Tethys subduction. The location of the boundary between the Arabian and central Iranian lithospheres is beneath the UDMA, which is shifted northeastward relative to the surficial expression of the MZT.https://jesphys.ut.ac.ir/article_51594_30337c0598b9fdec80617a263c127036.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X40320141023Comparison of derivative-based methods by normalized standard deviation approach for edge detection of gravity anomaliesComparison of derivative-based methods by normalized standard deviation approach for edge detection of gravity anomalies13215159510.22059/jesphys.2014.51595FAJournal Article20091223This paper describes the application of the so-called normalized standard deviation (NSTD) method to detect edges of gravity anomalies. Using derivative-based methods enhances the anomaly edges, leading to significant improvement of the interpretation of the geological features. There are many methods for enhancing the edges, most of which are high-pass filters based on the horizontal or vertical derivatives of gravity data. The normalized standard deviation, a new edge detection filter, is based on the moveable windows through gradient data, i.e. gravity gradient. The NSTD method (as an equation of the ratio of the related normalized standard deviations of the gravity data gradients) along with comparable techniques, including analytic signal, total horizontal derivative (THD), tilt angle, total horizontal derivative of tilt angle (THDT) and theta map, are examined for noise-free and noise-added synthetic data. The aim is to demonstrate the suitability of the NSTD in edge enhancement. Having obtained satisfactory results, the methods are applied successfully to the real gravity data of Dehloran Bitumen and the Karst zones in SabzKoh. The main aim of the edge detection methods in our study is to determine the appropriate locations of exploratory drillings in gravity prospect. It is demonstrated that suitable locations are determined based on these methods.This paper describes the application of the so-called normalized standard deviation (NSTD) method to detect edges of gravity anomalies. Using derivative-based methods enhances the anomaly edges, leading to significant improvement of the interpretation of the geological features. There are many methods for enhancing the edges, most of which are high-pass filters based on the horizontal or vertical derivatives of gravity data. The normalized standard deviation, a new edge detection filter, is based on the moveable windows through gradient data, i.e. gravity gradient. The NSTD method (as an equation of the ratio of the related normalized standard deviations of the gravity data gradients) along with comparable techniques, including analytic signal, total horizontal derivative (THD), tilt angle, total horizontal derivative of tilt angle (THDT) and theta map, are examined for noise-free and noise-added synthetic data. The aim is to demonstrate the suitability of the NSTD in edge enhancement. Having obtained satisfactory results, the methods are applied successfully to the real gravity data of Dehloran Bitumen and the Karst zones in SabzKoh. The main aim of the edge detection methods in our study is to determine the appropriate locations of exploratory drillings in gravity prospect. It is demonstrated that suitable locations are determined based on these methods.https://jesphys.ut.ac.ir/article_51595_d4069bb64abc5133ff9f6509302fd777.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X40320141023A method for 2-dimensional inversion of gravity dataA method for 2-dimensional inversion of gravity data23335159610.22059/jesphys.2014.51596FAJournal Article20101212Applying 2D algorithms for inverting the potential field data is more useful and efficient than their 3D counterparts, whenever the geologic situation permits. This is because the computation time is less and modeling the subsurface is easier. In this paper we present a 2D inversion algorithm for interpreting gravity data by employing a set of constraints including minimum distance, smoothness, and compactness. Using different combination of these constraints provide either smooth images of the underground geological structures or models with sharp geological boundaries. We model the study area by a large number of infinitely long horizontal prisms with square cross-sections and unknown densities. The final density distribution is obtained by minimizing an objective function that is composed of the model objective function and equality constraints, which are combined using a Lagrangian multipliers. Each block's weight depends on depth, a priori information on density and the allowed density ranges for the specified area. A MATLAB code has been developed and tested on a synthetic model consists of vertical and dipping dikes. The algorithm is applied with different combinations of constraints and the practical aspects are discussed. Results indicate that when a combination of constraints is used, the geometry and density distribution of both structures can be reconstructed. The method is applied on Zereshlu Mining Camp in Zanjan - Iran, which is well known for the Manganese ores. Result represents a high density distribution with the horizontal extension of about 30 m, and the vertical extension shows a trend in the E - W direction with a depth interval between 7 to 22 m in the east and 15 to 35 m in the west.Applying 2D algorithms for inverting the potential field data is more useful and efficient than their 3D counterparts, whenever the geologic situation permits. This is because the computation time is less and modeling the subsurface is easier. In this paper we present a 2D inversion algorithm for interpreting gravity data by employing a set of constraints including minimum distance, smoothness, and compactness. Using different combination of these constraints provide either smooth images of the underground geological structures or models with sharp geological boundaries. We model the study area by a large number of infinitely long horizontal prisms with square cross-sections and unknown densities. The final density distribution is obtained by minimizing an objective function that is composed of the model objective function and equality constraints, which are combined using a Lagrangian multipliers. Each block's weight depends on depth, a priori information on density and the allowed density ranges for the specified area. A MATLAB code has been developed and tested on a synthetic model consists of vertical and dipping dikes. The algorithm is applied with different combinations of constraints and the practical aspects are discussed. Results indicate that when a combination of constraints is used, the geometry and density distribution of both structures can be reconstructed. The method is applied on Zereshlu Mining Camp in Zanjan - Iran, which is well known for the Manganese ores. Result represents a high density distribution with the horizontal extension of about 30 m, and the vertical extension shows a trend in the E - W direction with a depth interval between 7 to 22 m in the east and 15 to 35 m in the west.https://jesphys.ut.ac.ir/article_51596_5283c8f25aa8bf0cdee0dcbb98bbf142.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X40320141023Gravity acceleration at the sea surface derived from satellite altimetry data using harmonic splinesGravity acceleration at the sea surface derived from satellite altimetry data using harmonic splines35465159710.22059/jesphys.2014.51597FAJournal Article20130616Gravity acceleration data have grand pursuit for marine applications. Due to environmental effects, marine gravity observations always hold a high noise level. In this paper, we propose an approach to produce marine gravity data using satellite altimetry, high-resolution geopotential models and harmonic splines. On the one hand, harmonic spline functions have great capability for local gravity field modeling. On the other hand, the information from satellite altimetry is a viable source of information for the marine gravimetry in the high-frequency gravity field modeling. Marine geoid from satellite altimetry observations can be converted to disturbing potential via ellipsoidal Bruns’s formula. The reference gravity field’s contribution is removed and restored after solving Dirichlet Boundary Value Problem. Finally, the results are downward continued to the sea surface using free air scheme. Computation of gravity acceleration in the Persian Gulf and its compatibility with the shipborne data shows reasonable performance of this methodology.Gravity acceleration data have grand pursuit for marine applications. Due to environmental effects, marine gravity observations always hold a high noise level. In this paper, we propose an approach to produce marine gravity data using satellite altimetry, high-resolution geopotential models and harmonic splines. On the one hand, harmonic spline functions have great capability for local gravity field modeling. On the other hand, the information from satellite altimetry is a viable source of information for the marine gravimetry in the high-frequency gravity field modeling. Marine geoid from satellite altimetry observations can be converted to disturbing potential via ellipsoidal Bruns’s formula. The reference gravity field’s contribution is removed and restored after solving Dirichlet Boundary Value Problem. Finally, the results are downward continued to the sea surface using free air scheme. Computation of gravity acceleration in the Persian Gulf and its compatibility with the shipborne data shows reasonable performance of this methodology.https://jesphys.ut.ac.ir/article_51597_48ab4d32c6bb6898d08bffa331bb8091.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X40320141023A resolution comparison of horizontal and vertical magnetic transfer functionsA resolution comparison of horizontal and vertical magnetic transfer functions47535159810.22059/jesphys.2014.51598FAJournal Article20101024The main goal of the present study is to identify characteristics of the inter-station horizontal magnetic responses and the vertical magnetic data, as two types of magnetotelluric transfer functions, in the modeling procedure. Through consideration of model responses and two-dimensional inversion of synthetic data, sensitivity of the data components in detecting different geophysical structures is investigated. An inversion of the magnetic transfer functions related to a real data set has been also accomplished, and the importance of a reference selection in analysis of the inter-station horizontal magnetic data has proved. Analysis of the results of the synthetic tests confirms the efficiency of the modeling based on horizontal magnetic responses and indicates more accuracy of this type of data, especially in terms of the resolution of the deep targets. There is not a great difference in the resolution of the structures between two datasets, as closely located anomalies are examined. Furthermore, both transfer functions can also sense vertical conductivity distribution.The main goal of the present study is to identify characteristics of the inter-station horizontal magnetic responses and the vertical magnetic data, as two types of magnetotelluric transfer functions, in the modeling procedure. Through consideration of model responses and two-dimensional inversion of synthetic data, sensitivity of the data components in detecting different geophysical structures is investigated. An inversion of the magnetic transfer functions related to a real data set has been also accomplished, and the importance of a reference selection in analysis of the inter-station horizontal magnetic data has proved. Analysis of the results of the synthetic tests confirms the efficiency of the modeling based on horizontal magnetic responses and indicates more accuracy of this type of data, especially in terms of the resolution of the deep targets. There is not a great difference in the resolution of the structures between two datasets, as closely located anomalies are examined. Furthermore, both transfer functions can also sense vertical conductivity distribution.https://jesphys.ut.ac.ir/article_51598_d51b33c79278926577ab723fa88fa32d.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X40320141023The omega blocking condition and extreme rainfall in Northwestern Iran during 25 - 28 October 2008The omega blocking condition and extreme rainfall in Northwestern Iran during 25 - 28 October 200855745159910.22059/jesphys.2014.51599FAJournal Article20120131Heavy precipitation plays a significant role in arid and semi-arid regions of Iran. In order to understand the effect of blocking high system on rainfalls in northwest Iran during 25 - 28 October 2008, meteorological conditions including pressure, wind fields and temperature at multiple levels of the atmosphere were analyzed. Sea level pressure, the 1000-500 hPa thickness, perceptible water, relative humidity, temperature, u and v components of wind at 850 hPa, geopotential height at 500 hPa and relative vorticity of u and v were obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis dataset. Location and displacement of the atmospheric systems such as cyclones, anticyclones, fronts and wind fields were identified using synoptic charts. Daily rainfall data obtained over 50 weather stations. Results indicate that the existence of a blocking high over the northern portion of the Caspian Sea caused the activity of two accompanying low pressure systems in which the western low resulted in excessive and intensive rainfall over the study area for 4 days. The low pressure was built by suitable wind patterns in the underlying levels (850 hPa). Moreover, modeling the outputs of 24-hour rainfall by the Geographic Information Systems (GIS) indicates that during the examined period northeastern parts of the region received the maximum rainfall.Heavy precipitation plays a significant role in arid and semi-arid regions of Iran. In order to understand the effect of blocking high system on rainfalls in northwest Iran during 25 - 28 October 2008, meteorological conditions including pressure, wind fields and temperature at multiple levels of the atmosphere were analyzed. Sea level pressure, the 1000-500 hPa thickness, perceptible water, relative humidity, temperature, u and v components of wind at 850 hPa, geopotential height at 500 hPa and relative vorticity of u and v were obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis dataset. Location and displacement of the atmospheric systems such as cyclones, anticyclones, fronts and wind fields were identified using synoptic charts. Daily rainfall data obtained over 50 weather stations. Results indicate that the existence of a blocking high over the northern portion of the Caspian Sea caused the activity of two accompanying low pressure systems in which the western low resulted in excessive and intensive rainfall over the study area for 4 days. The low pressure was built by suitable wind patterns in the underlying levels (850 hPa). Moreover, modeling the outputs of 24-hour rainfall by the Geographic Information Systems (GIS) indicates that during the examined period northeastern parts of the region received the maximum rainfall.https://jesphys.ut.ac.ir/article_51599_30ec6f065f9d3b2a7d27ef0e4426abaf.pdf