فصلنامه فیزیک زمین و فضا
سال چهل و پنجم شماره 4 (زمستان 1398)

Receiver functions are usually used to detect Ps converted waves and are especially useful to picture seismic discontinuities in the crust and upper mantle. In this study, the P receiver function technique beneath the west Iran is used to map out the lateral variation of the Moho boundary. The teleseismic data (Mb ≥5.5, epicentral distance between 30˚-95˚) recorded from 2004 to 2016 at 17 permanent broadband and short-period stations of the Iranian Seismological Center (ISC, http://irsc.ut.ac.ir) of Kermanshah, Khoramabad, Hamedan and Boroujerd and one broadband station of the International Institute of Earthquake Engineering and Seismology (IIEES, http://www.iiees.ac.ir) were used. The results indicate clear Ps conversions at the Moho boundary. The Moho depths are estimated from the delay time of the Moho converted phase relative to the direct P wave beneath each network. The average Moho depth lies at ~42±2 km. Furthermore, the clear image of the Moho at depths as modeling of PRF, ranging from 37 km beneath KCHF station to maximum 55 km beneath HAGD station was presented. According to the distribution and number of stations used, this study is more comprehensive than previous studies.

Computed Magnetic Gradient Tensor (CMGT) includes the first derivatives of three components of magnetic field of a body. At the eigenvector analysis of Gravity Gradient Tensors (GGT) for a line of poles and point pole, the eigenvectors of the largest eigenvalues (first eigenvectors) point precisely toward the Center of Mass (COM) of a body. However, due to the nature of the magnetic field, it is shown that these eigenvectors for the similar shaped magnetic bodies (line of dipoles and point-dipole), in CMGT, are not convergent to COM anymore. Rather, in the best condition, when there is no remanent magnetization and the body is in the magnetic poles, their directions are a function of data point locations. In this study, by reduction to the pole (RTP) transformation and calculation of CMGT, a point is estimated that its horizontal components are exactly the horizontal components of the COM and its vertical component is a fraction of the COM vertical component. These obtained depth values are 0.56 and 0.74 of COM vertical components for a line of dipoles and point-dipole, respectively. To reduce the turbulent effects of noise, “Moving Twenty five Point Averaging” method and upward continuation filter are used. The method is tested on solitary and binary simulated data for bodies with varying physical characteristics, inclinations and declinations. Finally, it is imposed on two real underground examples; an urban gas pipe and a roughly spherical orebody and the results confirm the methodology of this syudy.

This research deals with assessment of geothermal potential in parts of middle Benue Trough, north-east of Nigeria. The study area lies within the Longitude 9°E – 10°E and Latitude 8°N – 9.50°N with an estimated total area of 18,150 km2. Regional/Residual separation was performed on the total magnetic intensity using polynomial fitting. The residual map was divided into 14 overlapping spectral blocks, and the log of spectral energies were plotted against frequency. Centroid depth and depth to top boundary obtained were used to estimate the Curie point depth isotherm, which was then used to compute geothermal heat flow of the study area. The result shows that the geothermal heat flow varies between 50.02 and 85.1 mWm-2 with highest value in the southern part (Akiri and Ibi) and north-western part (Pankshin) of the area. The geothermal heat flow obtained from this study indicates that the study area possess a good source of geothermal potential. The aero-radiometric data covering the study area was also analysed to estimate the radiometric heat contribution. The analysis of aero-radiometric data shows that the area possesses high content of Uranium, Potassium and Thorium. The radioactive heat production values vary between 1.58 μW/m3 and 2.53 μW/m3 with an average of 2.21 μW/m3. Thus, harnessing the geothermal potential in this area would be of added values and advantage to power generation in Nigeria.

A 2D forward modeling code for DC resistivity is developed based on the integral equation (IE) method. Here, a linear relation between model parameters and apparent resistivity values is proposed, although the resistivity modeling is generally a nonlinear problem. Two synthetic cases are considered for the numerical calculations and the results derived from IE code are compared with the RES2DMOD that is a standard software for 2D resistivity forward modeling. For the first synthetic case, a model of resistive block surrounded by a homogenous medium is considered in different depths from 0.5 m to 4 m. For the nearest case to the surface, the IE pseudo-section is similar to its counterpart derived by RES2DMOD but its RMS error is a large value of 13.9 %. Increasing the depth of the anomaly results in decreasing of RMS values to 5.4 % for the deepest case and it is in correspondence with diminishing of the nonlinearity effects of electric fields for larger distances from the sources. The second model is composed of four conductive anomalies embedded in different depths. Visual comparison of IE response with software is indicative of high similarity of them, and RMS error for this relatively complex model is 7.5%, which can be an acceptable misfit for a linear forward operation. A very simple inversion algorithm using linear forward operator is applied on a real data set of a landfill survey in Germany collected by Wenner alfa array to demonstrate its productivity for practical applications. Reconstructed model using IE method is comparable with the inverted model derived by RES2DINV software, and it represents a good similarity with the original model.

In this study, soil characteristics were investigated using four well-located earthquakes recorded by six accelerometers located in North Cyprus. The amplification values obtained according to the soil features were mapped in accordance with different frequencies using horizontal to vertical spectral ratio method. The dominant period values of the units below the station locations were calculated in order to prevent the resonance effect of structures under dynamic loads. In general, high amplifications were observed in the low-frequency range in the loose units, while low amplifications were calculated in the compact units. High amplification values were detected at low frequencies in accelerometer stations located above the Quaternary alluvium and gypsum marls in Nicosia. Since the soil dominant period varies from 0.1 s to 0.3 s, structuring between 1 and 3 floors should be avoided in this area. The dominant period values for Erenkoy and Famagusta are 1.1 and 0.6; therefore, structuring between 11 and 6 floors should be refrained, respectively.

A new approach with the ability to use the multiple observations based on the least square approach has been proposed for initial orbit determination. This approach considers the Earth’s Oblateness by using the developed Lagrange coefficients. The efficiency of the proposed method has been tested in two scenarios. The first scenario is to use the simulated and the second one is to utilize the real angle-only observations for the GRACE-like and GPS-like satellites. Under the first scenario, the ground-based observations are produced using the reduced-dynamic orbit generated by GFZ. Then, various error levels were added to the produced azimuth and elevation observations. The results show that considering the Earth’s oblateness could improve the accuracy of the initial orbit determination by six times for a GRACE-like satellite, and by 60 times for a GPS-like satellite. Afterward, under the second scenario, the real observations of the SLR station were used. In view of increasing in the number of observation tests, by increasing the numbers of the observations from 3 to 15, the accuracy of initial orbit determination was improved from 1496 to 8 m using the SLR data for the GRACE-A satellite.

Determination of soil moisture content is of vital importance to many fields of study; civil engineering, hydrology, agriculture, geology, ecology and forestry. The occurrence of impact crater in Bukit Bunuh, a meteorite impacted area, made it an area of great interest to many researchers. In view of the process of impact cratering, the subsurface soil characteristics such as moisture content of the impacted area are prone to change and therefore prompted for this study. 2-D resistivity survey, borehole and laboratory test were used for the study. The outcome revealed that the subsurface soil inside the crater has high moisture content of 29 – 59 %, which corresponds to low resistivity values of < 300 Wm at a depth of < 20 m. This is probably caused by the geological processes involved in the impact cratering, which made the soil to be loose, porous and permeable, thus enhancing the moisture content. The soil overlying the crater rim and outside the crater has higher resistivity values > 300 Wm, which is indicative of low moisture content (< 29 %). The highly resistive soil is more pronounced on the crater due to the reclaimed soil during the impact cratering. Based on the data analysis, significant correlation between the soil moisture content and the electrical resistivity was established.

Thermal conductivity measurements have been used for the Way Ratai geothermal prospect area. The thermal conductivity method is used to evaluate the ability of a rock to deliver heat by conduction. In the area, many surface manifestations are scattered in various regions, where hot springs dominate these various manifestations. The thermal conductivity mapping of rocks is carried out around geothermal manifestations by making a hole as deep as 1 m to insert the stick of conductivity meter. The result of thermal conductivity measurement method is data of k (thermal conductivity), Rt (thermal resistivity), and T (temperature). The measured value of conductivity data in the geothermal field is valued between 0.056 and 0.664 W/mK, thermal resistivity between 1.344 and 17.527 mK/W, and the temperature between 22.7 and 52.6°C. The difference in the value of thermal conductivity rock is influenced by several factors: existing geological structures in the field such as normal faults and lineaments, presence of alteration, and the manifestation zone of hot water or hot vapor that caused by fumaroles.

Extracting the main cyclic fluctuations from sea level changes of the Persian Gulf and Oman Sea is vital for understanding the behavior of tides and isolating non-tidal impacts such as those related to climate and changes in the ocean-sea circulations. This study compares two spectral analysis methods including: Least Squares Spectral Analysis (LSSA) and Least Squares Harmonic Estimation (LSHE), to analyze satellite altimetry derived sea surface height changes of the Persian Gulf and Oman Sea. SSH data are derived from about 16 years of satellite altimetry observations (1992 to 2008), including the Topex/Poseidon and Jason-1 missions. By analyzing the real data, we extract significant tidal components in the spectrum of LSSA and LS-HE including those with the period of 62.07, 173.3, 58.71, 45.68, 88.86, 364.2 and 117.5 days, which are interpreted as Principal Lunar semi-diurnal, Luni-Solar Diurnal, Principal Solar Semi-diurnal, Principal Lunar Diurnal, GAM2, annual, Solar Diurnal periods are dominant in the level fluctuations. Moreover, some tidal components appear in the spectrum of LSSA and LS-HE, from which the Moon's semi-diurnal component  is dominant. Also, to evaluate the efficiency of these two techniques, we run three experiments in each extracted frequency from LSSA, LS-HE, and astronomical tide tables are separately used to predict the sea level in the Persian Gulf and Oman Sea for three years. The results of this prediction indicate that RMSE from LSSA, astronomical table, and LS-HE is 0.101 m, 0.093 m, and 0. 086 m, respectively. According to the results LS-HE is found a more efficient technique to analyze cyclic fluctuations from altimetry measurements.

In this study, an inversion method is conducted to determine the focal mechanism of Sefid-Sang fault by comparing interferometric synthetic aperture radar (InSAR) technique and dislocation model of earthquake deformation. To do so, the Sentinel-1A acquisitions covering the fault and its surrounding area are processed to derive the map of line of sight (LOS) displacement over the study area. Then, using the ascending and descending tracks of the satellite, the three-dimensional displacement field is recovered over the region. The maximum horizontal and vertical displacements are about 12 cm and 5 cm respectively. The resulting displacement field is compared with Okada half-space dislocation model of earthquake to determine the focal mechanism and fault parameters by a nonlinear inversion method, which is composed of artificial neural network (ANN) and genetic algorithm (GA). The coulomb stress and strain changes, which are important factors for prediction of aftershock event, are also determined. The numerical achievements show a slip of 4.5 mm, a depth of 8 km, dip angle of 55 deg and width of 10 km for this fault.

In this study, we obtained two-dimensional tomography maps of the Rayleigh wave group velocity for the northwest part of the Iranian Plateau in order to investigate the structure of the crust and the uppermost mantle of NW Iran. To do this, the local earthquake data during the period 2006-2013, recorded by the 10 broadband stations of the Iranian seismic network (INSN) were used. After the preliminary correction, Rayleigh wave group velocity dispersion curves for each source-station path using the time-frequency analysis (FTAN) were estimated. Then, using a 2D-linear inversion procedure, the lateral variations in the group velocity distribution at different periods were calculated. The results are consistent with the previous studies and show major structural units in this region. Our results for the lower periods show distinct velocity anomalies along the North Tabriz Fault (NTF) and beneath the Sahand and Sabalan Volcanoes. Also, along the boundary of the Urumieh-Dokhtar Magmatic Arc (UDMA) and the Sanandaj-Sirjan metamorphic Zone (SSZ), lateral velocity changes are observed. The results for the longest period (the uppermost mantle) show low-velocity anomalies for most parts of the study area.

This work presents the study of the variability of foF2 and hmF2 at a low latitude station in South America (Tucumán, 26.9°S, 294.6°E; magnetic latitude 15.5°S, Argentina). Ground based ionosonde measurements obtained during different seasonal and solar activity conditions (a year of low solar activity, 2009 and one of high solar activity, 2016) are considered in order to compare the ionospheric behavior. The parameters used to analyze the variability are the median, upper and lower quartiles. In addition, the foF2 values are compared with those estimated by the International Reference Ionosphere (IRI) - 2016 model. It is found that: a) A clear dependence on solar activity is observed in foF2 and hmF2, both increase with increase in solar activity. b) the variability of foF2 is higher at low solar activity, this behavior is not observed in hmF2 that present similar variability during both periods. c) the variability of foF2 is larger at night than during the day, this behavior is more pronounced during the high solar activity period. d) The variability of foF2 is higher than that of hmF2. e) Significant planetary wave spectral peaks at about 2 and 5 days are observed at high and low solar activity. f) In general, IRI overestimates foF2 during daytime, and underestimates it at post-sunset period, a better agreement is shown during nighttime.

Considering the great application of Sea Surface Temperature (SST) in climatic and oceanic investigations, this research deals with the investigation of spatial autocorrelation pattern of SST data obtained from AVHRR sensor for Gulf of Oman from 2003 to 2015 (13 years). To achieve this aim, two important spatial statistics, i.e. global Moran and Anselin local Moran’s I were employed within monthly and annually timescales. The results obtained from global Moran in the monthly scale suggested the existence of a strong autocorrelation and cluster pattern for SST data across all months, where warm months had a stronger autocorrelation in comparison with cold months. Furthermore, global Moran index within annual scale indicated an ascending trend for autocorrelation and clustering of SST data within the 13 studied years. To represent the manner of clustering, local Moran index was employed. Based on the results of this index within monthly scale, it was found that in winter, especially during January and February, low-low clusters, which represent low SST values, have been formed in western parts, while high-high clusters, which represent high SST values, have been formed in the southeastern parts of Gulf of Oman. After this season, the mentioned pattern changed, and from May to October, low-low clusters have been developed in the southeastern parts, while high-high clusters have been developed in the western parts of Gulf of Oman. The map of clusters for the annual scale suggested the growth of high-high clusters and reduction of low-low clusters of SST overtime. Based on these findings, it could be concluded that warming of SST in Gulf of Oman within this time period has been statistically significant and positive.

Total electron content (TEC) and GNSS positioning error over two Nigeria GNSS stations (CLBR: Latitude; 4.9503°E, Longitude; 8.3514°N, FUTY: Latitude; 9.3497°E, Longitude; 12.4978°N) were studied during the geomagnetic storms of March 17, 2015 minimum Dst (Disturbed storm time) -223nT and that of March 17, 2013 minimum Dst of -132nT (the St. Patrick’s Day intervals); TEC was estimated using GPS Gopi TEC analysis software over the two stations during the storms period and the selected international quiet day used as reference. Understanding TEC variation in the equatorial ionosphere during geomagnetic storm will enable adequate prediction of GNSS positioning accuracy and correction over the region. Variation and enhancement of TEC were observed during the storms. The positioning error and TEC were higher at CLBR than at FUTY during the March 17, 2015 storm that could be as a result of latitudinal variation. The result will be useful for satellite based navigational systems.

In the present study, in order to monitor and project climate change impacts on model of the bioclimatic design, a comparative study was conducted between the Middle East and Eurasia as two different climates. This paper used the basic data from 1990 to 2010, and the CMIP5 climate models have been used to project the climate data (radiation, temperature, wind speed, and relative humidity) from the outputs of CanEMS2 model, which its values have been dynamically downscaled using the RegCM4.6 climate model for the period from 2020 to 2049. In this study, the scenario RCP4.5 was used. The results of this study showed that the average annual temperature for the period 2020–2049 as compared with the present decade can be increased 3.27 °C and 4.71 °C for Tehran and Moscow, respectively. On the other hand, relative humidity changes in future compared to base period can be decreased 4% for Tehran and increased 10.5% for Moscow. The total assessment on climate change in the coming decades can lead to a change in bioclimatic design strategies of buildings for both study areas. Generally, with regard to future climate change for both study areas, the percentage of days needed to provide bioclimatic design strategies in the heating sector can be reduced; however, the need for providing cooling strategies for Tehran can significantly be increased. Although these conditions for Moscow can not change significantly, dehumidification strategies in Moscow can be more significant than of those in Tehran for the coming period.

In the old Lut playa underneath the hills of nebkhas, the deepening of the waterways and the extent of the expansion of the cones and the nebkha morphometry are evidences of environmental changes. To study the above-mentioned factors, it is necessary to rebuild the morphodynamic conditions of the region. In this research, the changes in environmental conditions of the area are investigated and rebuilt using the phytogenic hills of nebkha. Sampling was done by carving a surface on the sediments of nebkhas and specifying their layers. The sampled sediments were then studied in a geochemical lab and their age was estimated in a lab in Poznan in Poland, where they were sent. The results show that the region in a period of 735 years of the life of the Nebkhas has gone through several levels of environmental changes. The most intense processes and the wettest period among the studied periods belong to the third period about 735 years ago. These results were gathered by geochemical experiments such as the amount of organic matter, salt and lime on the layers of the sediments. The driest period among the periods studied is the 11th period, which took place around 114 years ago. The least intense processes with the lowest amount of humidity (according to the results related to the amount of organic matter in the sediments) were in this period.

The global warming phenomenon has had a great impact not only on the temperature patterns of the regions, but also on the spatial-temporal patterns of the occurrence of wet and dry days. As some areas have increased (decreased) the number of dry days, the result of these changes requires new approaches to water management in these areas. Golestan province in northern Iran is one of the provinces in south of Caspian Sea, where evidence suggests a decrease in precipitation days as well as the temporal displacement of precipitation days from the cold period to the warm period of the year. Therefore, the present study investigates the probability of occurrence of wet and dry days based on the one-time Markov chain method, as a change of decade. Thus, in this research, precipitation data from 197 precipitation stations for a period of 40 years from 1971 to 2010 was used. In this study, based on the most internal consistency of different regions in terms of the occurrence of wet and dry days, eight different spatial zones were identified. The results of this study indicate that the continuity of the wetter periods in the eight-cluster zones of Golestan province indication that the length of the wetter period has decreased in most months. The highest decrease in July was on average 0.20 days per decade. However, in August, September, and October, it reached its lowest level. In August and September, clustered zones in the eastern regions of the province show an increase in the longer period. This indicates that during the last decades throughout the second half of the summer, rainfall has increased in the province.

This paper reports on the progress for the first development of rocket probe for in-situ measurement of ionospheric plasma parameters in Iran. The designed probe known as Plasma Impedance Probe (PIP) will be used to measure the electron density, electron-neutral collision frequency, background magnetic field, and temperature in the mesospheric and in the altitude range of 70 km to 150 km. This paper presents a review of the current plan on design, analysis, fabrication and laboratory tests of the PIP. Specifically, the theoretical calculations as well as numerical simulations on the characteristics of the PIP is provided and discussed. The effect of several background parameters in the ionospheric region on the radiation characteristics of the immersed antenna in the background plasma is presented. The possible reduction technique in order to analyze the observational data and derive background ionospheric parameters is provided. The requirements for the implementation of the designed probe are investigated. The possible applications of the PIP in complex plasma are introduced.