فهرست مطالب

فیزیک زمین و فضا - سال چهل و سوم شماره 4 (زمستان 1396)

فصلنامه فیزیک زمین و فضا
سال چهل و سوم شماره 4 (زمستان 1396)

  • تاریخ انتشار: 1396/11/09
  • تعداد عناوین: 8
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  • Ayoub Hosseini Mehr, Behnam Maleki Asayesh *, Mohammad Mokhtari Pages 1-10
    The Makran subduction zone in northeast and the Sumatra subduction zone (Sunda) in the west have been known as tsunamigenic zones of the Indian Ocean. The 990 km long Makran subduction zone is located offshore of Iran, Pakistan and Oman. Similar to many subduction zones all over the world, the Makran accretionary prism is associated with an imbricate of thrust faults across the zone, which may rupture due to great earthquakes. Based on some studies, it has been suggested that the presence of young marine terraces along parts of the western Makran, Jask, and Konarak, providing a strong evidence for the occurrence of great thrust earthquakes in the western Makran. Besides, this region might have experienced a strong earthquake in 1483 (Mw=7.2). This study uses 2D seismic reflection data to map the splay faults in the western Makran subduction zone. The result of this interpretation has been presented on map showing the major splay and normal faults, in the south and north, respectively. Furthermore, Coulomb stress changes is calculated along the splay faults, following a hypothetical earthquake (Mw=7.2) on the megathrust. The amount of slip that transfers from the plate boundary onto the splay faults during large subduction earthquake and the pattern of slip partitioning between them are calculated. The results show that the slip on Megathrust increases stress in some parts of surrounding areas. Some splay faults are located in these areas that can be loaded in shallow depth and are likely the sources of aftershocks. Since the slip on splay faults has a key significance in generating tsunami, their analysis is an important issue in tsunami risk assessment. It is strongly suggested that the result of this study is used as an input parameter for a comprehensive tsunami hazard modeling in the Makran region.
    Keywords: Subduction zone, Splay faults, Seismic reflection data, Coulomb stress changes
  • Mostafa Ebrahimi, Ali Moradi *, Hamid Seidin Pages 11-26
    Nowadays, viable and cost-effective methods play a vital role in hydrocarbon exploration up to the point that geoscientists cannot rule out the importance of the passive seismic method (PSM) in oil exploration operations. This method is based on seismic energy, which has a natural source. This study focuses on seismic energy anomaly of 1-6 Hz. Some researches show that spectral and polarization analysis in low-frequency of seismic noises can be used in determining the location of hydrocarbon reservoir. In this paper, these methods were used in Maroun oil field. Using the seismic data recorded by five seismometers, Vertical-to-Horizontal spectral ratio (V/H), Power Spectral Density (PSD) and polarization analysis were studied in the mentioned area. Based on the results, these microtremors can be used as a hydrocarbon indicator. In this study, transient and artificial noises are removed from raw data with various techniques. Afterward, the vertical-to-horizontal spectral ratio method was used and the results were analyzed and compared. Subsequently, the PSD method was investigated and its results were compared with each other at different stations. Following this, polarization analysis was considered that was normally followed by parameters such as strength, dip, rectilinearity and azimuth in particular. Results showed that MAR5 Station was placed over an area with hydrocarbon potential and there are medium to low hydrocarbon potentials at other stations. There is also a positive correlation between passive seismic analysis and the result of seismic reflection surveys carried out in the earlier studies.
    Keywords: Passive Seismic, Maroun oilfield, Spectral analysis, Polarization analysis, PSD
  • Amir Karimiara, Mahmoud Mirzaei *, Mojtaba Babaei Pages 27-45
    A constrained nonlinear optimization method based on nonlinear programming techniques has been applied to map geometry of bedrock of sedimentary basins by inversion of gravity anomaly data. In the inversion, the applying model is a 2-D model that is composed of a set of juxtaposed prisms whose lower depths have been considered as unknown model parameters. The applied inversion method is a nonlinear one, which minimizes the objective functions by definition of different objective functions and an initial simple model to improve the initial model parameters. In this study, for different cases, sufficient objective functions are defined based on the condition which is encountered in the inverse problem. To control the under- determinacy part of the inverse problem and to prevent unreasonable instability in the resultant model, damping terms are added to the objective function. The act of synthetic inversion for different cases of parameterization has been examined and the results are analyzed. The results have almost depicted the recovery of the model and also fitting of the original and model response data. In addition, the method has been used to invert real gravity data in Aman Abad area. From the inversion results, depths of the basin, features like fractures and uplift in bedrock, along specific profiles have been determined. Thicker parts of sediments in the basin along the profiles have also been recognized, which have the potential for exploring drinking water in this area.
    Keywords: Optimization, Objective function, Geometry of bedrock, Inversion, Constrains, Gravity data
  • Poongavanam Sardar Maran * Pages 47-53
    Wind measurement is important for estimating wind energy potential, but it is relatively cost-intensive and often conducted at a narrow height from the ground level. The typical range of most turbine hub heights is from 30-50 m or even higher. Extrapolation on wind data thus becomes necessary to estimate the wind speed at different heights. Doing so requires the essential understanding of wind shear characteristics representative to a location or a region. The analysis is carried out from the vertical profile of meteorological observation collected from 50 m tower at Sathyabama University during the period of 2010-2014. The tower is located near the coastal region in Chennai. The tower is equipped with instruments to measure several meteorological variables. For wind speed and direction, they are routinely measured at different heights, which are considered well suitable for wind shear characterization. In this work, the characteristics of wind shear exponent at the tower were investigated and discussed, with emphasis on temporal (diurnal and monthly) variation and spatial distribution.
    Keywords: Wind Energy, Wind Shear, Surface Roughness, Meteorological Tower
  • Mohammadreza Azizzadeh, Khadijeh Javan * Pages 55-72
    The variability of temperature extremes has been the focus of attention during the past several decades and had a great influence on the hydrologic cycle. A long-term, high-quality daily maximum (TX) and minimum temperature (TN) of seven stations was used to determine the spatial and temporal characteristics of extreme temperature events in Lake Urmia Basin in Iran during 1987 to 2014. The RClimdex was used to calculate 16 extreme temperature indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI) for this study and the Mann-Kendall test was employed to assess the trend. All the temperature-based indices show patterns consistent with a general warming trend. The results revealed statistically significant changes in important temperature indices over the study area during the past three decades. On the whole, cold indices, including cool days, cool nights, ice days, frost days and cold spell duration index significantly decreased by -3.07, -2.27, -1.8, -1.53 and -0.16 days/decade, respectively. In contrast, warm indices such as warm days, warm nights, summer days, tropical nights, warm spell duration index, and growing season length significantly increased by 2.99, 3.34, 3.3, 3.06, 2.63 and 1.79 days/decade. Minimum TX, maximum TX, Minimum TN and maximum TN increased significantly by 1.00, 1.76, 0.36 and 1.01 °C/decade. Furthermore, the magnitudes of the trends in cold/warm days are larger than those in cold/warm nights, which indicate that the trends in minimum temperature extremes are more rapid than in maximum temperature extremes. Strong relationships between the annual mean temperature and the extreme temperature indices were detected in this study.
    Keywords: Temperature extremes, Trends, Mann-Kendall test, Lake Urmia Basin
  • Majid M. Farahani *, Nafiseh Pegahfar, Maryam Gharaylou Pages 73-81
    This study introduces a new technique to fill and reconstruct daily observational of Total Ozone records containing void data for some days based on the wavelet theory as a linear time-frequency transformation, which has been considered in various fields of science, especially in the earth and space physics and observational data processing related to the Earth and space sciences. The initial corrupted records consist of six years of daily total Ozone measured by Dobson Photo-Spectrometer Instrument of Institute of Geophysics, University of Tehran. To verify the filled gaps resulted from this technique, the outputs of the proposed method are compared with the Total Ozone Mapping Spectrometer (TOMS) for the year 2005 and Ozone Monitoring Instrument (OMI) for the years 2006 – 2010 satellite data (hereafter used as TOMS/OMI data). The proposed technique consists of three steps: (1) quality control and denoising; (2) data-reconstruction based on Daubechies parent function (DB1); and (3) the combination of approximation and complementary coefficients using the Inverse Discrete Wavelet Transform (IDWT). Results show that this method was able to successfully reconstruct the missing data for gaps lasting no greater than 18 days. For gaps beyond this 18-day limit, however, this method was unable to reconstruct the voided data. As most instruments, including Dobson and Brewer Spectrometer, are working based on the optical interaction of stratospheric Ozone and sunshine, gaps in the Total-Ozone for more than 18 days should happen in atmospheric systems with longevity over 18 days in which overcast clouds persist longer than the 18-day limit. The proposed method could be applied with high efficiency.
    Keywords: Total-Ozone, Discrete wavelet transform, Missing data, Interpolation, Signal reconstruction
  • Mojdeh Hafezi, Alireza Mohebalhojeh *, Abbas Ali Aliakbari-Bidokhti, Parviz Irannejad, Samaneh Sabetghadam Pages 83-95
    The large-scale tropospheric circulation can play a controlling role in the accumulation and ventilation of air pollutants. It thus impacts air quality in large urban areas. This paper investigates the statistical relations between the dynamical indices related to circulation in the troposphere and visibility as a surrogate for air pollution in the urban area of Tehran for the climatological period of 1958 to 2013. The dynamical indices are based on jet splitting and Rossby wave breaking at the upper troposphere, eddy kinetic energy, meridional momentum flux, and static stability at the lower troposphere, as well as the high and low surface pressure disturbances. Despite the definite impact of surface pressure disturbances on visibility in Tehran, results show only very weak, if any, relation between the tropospheric circulation indices and visibility in Tehran. The absence of a robust relation is attributed to the slow response of the urban ventilation process to the time evolution of dynamical indices above the boundary layer and particularly at upper troposphere. The complex terrain of the region is likely the main factor creating the slow response.
    Keywords: Tehran, Air pollution episodes, Dynamical indices, Blocking, Split flow
  • Mohammad Javad Kalaee * Pages 97-102
    Interactions of charge particles with electromagnetic waves have important effects (linear and nonlinear) on the propagation of electromagnetic waves, and it can somewhat play a role in generation of the new mode waves. Besides, the particle energies can play an important role in causing instability in plasma. The values of parallel energy of the particles have been calculated so that they can satisfy the nonlinear coupling condition. Furthermore, a result for instability is presented and the initial parameters inferred from the observational data are used. The results show that the nonlinear coupling (particle-wave interaction) can be a candidate for the generation of RX mode wave in equatorial plasmasphere. Besides, the results show that energetic particles that participate in particle - wave interaction have an energy range from 0.058 to 10.23keV. This range of particle energy particle is in agreement with the observation.
    Keywords: Particle energies, Instability, Nonlinear wave-particle