Time filter

Source Type

Beiki M.,Uppsala University | Pedersen L.B.,Uppsala University | Nazi H.,Geological Survey of Iran
Geophysics | Year: 2011

This study has shown that the same properties of the gravity gradient tensor are valid for the pseudogravity gradient tensor derived from magnetic field data, assuming that the magnetization direction is known. Eigenvectors of the pseudogravity gradient tensor are used to estimate depth to the center of mass of geologic bodies. The strike directions of 2D geological structures are estimated from the eigenvectors corresponding to the smallest eigenvalues. For a set of data points enclosed by a square window, a robust least-squares procedure is used to estimate the source point which has the smallest sum of squared distances to the lines passing through the measurement points and parallel to the eigenvectors corresponding to the maximum eigenvalues. The dimensionality of the pseudogravity field is defined from the dimensionality indicator I, derived from the tensor components. In the case of quasi-2D sources, a rectangular window is used in the robust least-squares procedure to reduce the uncertainty of estimations.Based on synthetic data sets, the method was tested on synthetic models and found to be robust to random noise in magnetic field data. The application of the method was also tested on a pseudogravity gradient tensor derived from total magnetic field data over the Särna area in west-central Sweden. Combined with Euler deconvolution, the method provides useful complementary information for interpretation of aeromagnetic data. © 2011 Society of Exploration Geophysicists.

A database of Iranian earthquakes during the instrumental period (1900-2014) is used to analyze geometric and kinematic aspects of the surface ruptures in different seismotectonic regions of the country. Majority of the ruptures have occurred along or associated with known geological or active faults. Thrust and strike-slip faults show a maximum surface rupture length of 85 and 125 km respectively. Excluding the distributed displacements on bedding thrusts during the 1979 Tabas earthquake, which was summed up differently to ~1.5 and ~3.0 m, maximum displacement on individual faults of thrust mechanism is 1.5 m, while strike-slip faults show a maximum horizontal displacement of 4.5 m. Surface rupture zone width of ~3 km is observed in an strike-slip event, and a ~4 km distance between the known active fault and the surface rupture of an event suggests that care should be taken in evaluation of setback zone for rupture hazards of some faults with complex geometry/kinematics. Partitioning in space and time of ruptures in earthquakes requires a better understanding of exact kinematics of active fault zones. While rerupturing of a fault segment in alternating events complicates the rupture history of the segment, simultaneous rupture of several fault segments and sympathetic faulting should be taken into account for evaluation of earthquake hazard in specific regions with such possible seismotectonic setting. Secondary ruptures and fractures, either in the presence or absence of primary surface ruptures, develop via different mechanisms, and complicate the surface deformations. While surface ruptures are frequently associated with earthquakes in eastern Iran, these features are very rare in Zagros and Makran regions. Empirical relations are suggested among surface rupture length, maximum displacement and moment magnitude for different earthquake fault mechanisms in Iran, which may be more compatible to the events within Iran. Using these relations the maximum surface rupture length, maximum surface displacement, and the associated maximum credible earthquakes are suggested for different regions in Iran. The suggested values may also be used for estimation of earthquake magnitudes in paleoseismological studies. © 2016 Elsevier B.V.

In order to investigate the environmental geochemistry of groundwaters in the urban areas of Kerman city, 50 samples of natural groundwaters, urban groundwaters and drinking waters were collected. High values of salinity (5. 8 ‰), electrical conductivity (10,270 μS/cm), total dissolved solids (TDS) (5,140 mg/kg), fluorine (4. 9 mg/kg), chlorine (3,974 mg/kg), bromine (1. 6 mg/kg) and sulfate (4,306 mg/kg) in the northern part of the studied area are caused by dissolution of evaporate bed rocks and Quaternary salt plains. Low values of salinity (0. 5 ‰), electrical conductivity (973 μS/cm), TDS (486 mg/kg), fluorine (0. 8 mg/kg), chlorine (297 mg/kg), bromine (0. 25 mg/kg) and sulfate (262 mg/kg) are only reported in the southern part of the Kerman city. High values of nitrate (NO3 -) range from 134 to 725 mg/kg and nitrite (NO2 -) content is variable between 0. 04 to 23. 45 mg/kg. These values indicate mixing of groundwaters with wastewaters. The heavy metal values in groundwaters around the Kerman city show 20. 5 μg/kg Cu, 5. 88 μg/kg Mo, 16. 2 μg/kg Pb, 70 μg/kg Zn, 11. 6 μg/kg Cr, 1. 99 μg/kg Co, 4. 13 μg/kg Ni, respectively. Furthermore, the natural aquifers of Kerman city contain 24 μg/kg Cu, 8. 15 μg/kg Mo, 18. 25 Pb, μg/kg, 193 μg/kg Zn, 14. 7 μg/kg Cr, 3. 97 μg/kg Co and 7. 45 μg/kg Ni, respectively. The results demonstrate that the main sources of contamination are related to the natural evaporates, mixing of groundwaters with wastewaters and constructional materials in the area. © 2012 Springer-Verlag.

Allen M.B.,Durham University | Talebian M.,Geological Survey of Iran
Geological Magazine | Year: 2011

Structure varies along strike in the Zagros fold-and-thrust belt of Iran, which is a principal element in the Arabia-Eurasia continental collision. Pre-collision, Late Cretaceous ophiolite nappes (Kermanshah, Neyriz) and related nappes of deep marine sediments (Radiolarite Series) were emplaced next to two regions (Pusht-e Kuh arc, Fars) which later developed a consistent structural style across the range from the High Zagros Fault to the foreland limit of deformation. The intervening area has a zone of highly imbricated Arabian plate strata (the Bakhtyari Culmination) thrust southwest towards and over a low relief, low elevation region (the Dezful Embayment). There are no ophiolite nappes northeast of the Bakhtyari Culmination. Isopachs reflect these different structural patterns from Late Cretaceous time but not earlier. In Late Cretaceous time the Dezful Embayment recorded less deposition than adjacent areas to the northwest and southeast. In the Palaeogene there was little net difference between the Dezful Embayment and its margins. The Dezful Embayment has been a depocentre since roughly 35 Ma, which is the likely time of initial collision between Arabia and Eurasia. We propose that the syn-collision structure and stratigraphy of the Zagros is therefore strongly influenced by the variation in Late Cretaceous ophiolite emplacement, but the original cause of this variation is not clear. © 2011 Cambridge University Press.

Keshavarzi B.,Shiraz University | Moore F.,Shiraz University | Najmeddin A.,Shiraz University | Rahmani F.,Geological Survey of Iran
Science of the Total Environment | Year: 2012

Selenium (Se) deficiency is reported by some authors to be an important factor in the etiology of esophageal cancer (EC) in the Golestan province of Iran. In order to further investigate the role of Se and selected trace elements in the occurrence of EC disease, 663 samples including 206 cultivated soils, 247 sediments, 45 loess deposits and 165 grain samples from 45 villages in the Golestan province of Iran were collected and analyzed. Villages in the study area were classified into 2 groups according to the EC incidence in the local population. The results of this study demonstrate that, contrary to the expected trend, total Se concentrations in soil, grain, sediment, and loess samples increase from the low to the high EC areas suggesting that Se deficiency does not play a major role in the etiology of EC. On the other hand, antimony (Sb), and strontium (Sr) content in soil, grain, loess, and sediment samples is much higher in the high esophageal cancer area, which may be a significant factor. Total zinc (Zn) concentrations in soil, grain, loess, and sediment samples decrease from the low to the high cancer areas. Therefore, Zn deficiency may be a significant factor in EC incidence rate in the Golestan province. © 2012 Elsevier B.V.

Discover hidden collaborations