فهرست مطالب

ژئوفیزیک ایران - سال دوازدهم شماره 5 (پیاپی 42، بهار 1398)
  • سال دوازدهم شماره 5 (پیاپی 42، بهار 1398)
  • تاریخ انتشار: 1398/03/01
  • تعداد عناوین: 7
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  • Parisa Hosseini, Reza Heidari *, Noorbakhsh Mirzaei Pages 1-10
    In this study, new empirical relationships to estimate key parameters in Earthquake Early Warning (EEW) system including magnitude, epicentral distance and Peak Ground Acceleration (PGA) are introduced based on features of the initial portion of P-wave’s amplitude envelope curve.
    For this purpose, 226 time series recorded by bore-hole accelerometers of Japanese KiK-net are processed for earthquakes with magnitudes from 3 to 7.2  and epicentral distances of less than 50 km. Hereby, an improved single station method for estimation of epicentral distance and two new methods for estimation of magnitude and amplitude of  are proposed based on exponentially envelope curve as  in known (B – Δ) method. A scaling relationship of B × Tr – Δ is proposed to estimate epicentral distance which is well correlated for larger earthquakes, with results more robust and reliable than the previous method (B – Δ). Non-dimensional parameter,  depends on earthquake magnitude and  parameter in the above-mentioned function. By using the features of acceleration envelope curve and peak amplitude of P-waves, scale parameter  is proposed that is well correlated with magnitude and has capability of estimating magnitude with standard deviation of less than 0.77 magnitude unit.  is proportional to a part of area under envelope curve as a function of magnitude. Moreover, it is indicated that  in a single station can be estimated by using envelope curve characteristics of initial P-waves portion.
    Keywords: Earthquake Magnitude, Envelope, B – Δ, Earthquake Early Warning System, Epicentral Distance, Peak Ground Acceleration
  • Omid Bagherpur, Banafsheh Habibian Dehkordy *, Behrooz Oskooi Pages 11-20
    Magnetotelluric measurements have been conducted in the period range of 0.005-128 s along five parallel east-west directed profiles including 85 sites totally in the north-eastern part of Gorgan Plain, Golestan Province, North of Iran; with the aim of exploring iodine. Distortion and dimensionality analysis of data imply the existence of a north-south elongated two-dimensional model with some localized three-dimensional effects, particularly at long periods, that has been mildly affected by non-inductive distortions. Exclusion of a very few data points with large values of distortion angles and rotation based on the selected azimuth of strike was followed by two-dimensional inversion of joint TE- and TM-mode apparent resistivity and phase data. After some resolution tests to ensure the reliability of the detected features, three-dimensional inversion of real and imaginary parts of full impedance tensor data was accomplished. Despite the reduced resolution of magnetotelluric data in a conductive environment, the elimination of part of the data due to hardware constraints and the lack of an ideal data acquisition pattern, the models showed some definite results. The resulted electrical resistivity models from both two- and three-dimensional inversion resolved highly conductive bodies as our exploration targets, which are expected to be saline aquifers containing iodine within the generally conductive sediments.
    Keywords: Magnetotellurics, Two-, three-dimensional inversion, Iodine exploration, Electrical conductivity
  • Hoda Mahmoodi, Habib Rahimi *, Behzad Maleki Pages 21-32
    In this paper, the shear wave quality factor and source parameters in the near field are estimated by analyzing the acceleration data in Zagros region. Accelerograms recorded by Building and Houses Research Center strong ground motion network have been used. The data have been considered with the magnitude of 4.7 to 6.3 collected from 1999 to 2014. In this approach, the theoretical S-wave displacement spectra conditioned by frequency independent Q was fitted with the observed displacement spectra. The source spectrum of an earthquake can be approximated by the omega-square ω2 model, which has ω2 decay for frequencies higher than the corner frequency. By following the mentioned approach, corner frequency, scalar moment, moment magnitude and frequency independent Q for each accelerogram were computed simultaneously, and the estimated error was given in the root-mean-square sense over the frequency range of interest. In this study, the generalized inversion method is used to estimate various source parameters as listed below. Thereby, it is estimated that the seismic moment range from 2.89E+23 to 1.21E+26 dyne-cm, average fault slip from 22 to 152 cm and average stress drop from 6 to 136 bars. The path average value Q are of the order Q=151-537.
    Keywords: Quality factor, Source Parameters, inversion method, Source spectrum
  • Mohammad Barazesh * Pages 33-49
    Recently, interpretation of causative sources using components of the gravity gradient tensor (GGT) has had a rapid progress. Assuming N as the structural index, components of the gravity vector and gravity gradient tensor have a homogeneity degree of -N and - (N+1), respectively. In this paper, it is shown that the eigenvalues, the first and the second rotational invariants of the GGT (I1 and I2) are homogeneous with the homogeneity degree of - (N+1), -2(N+1) and -3(N+1), respectively. Furthermore, the product of M homogeneous functions with a homogeneity degree of - (N+1) itself is homogeneous with the degree of –M(N+1), and their summation do not change the homogeneity degree. Therefore, the Euler deconvolution of these functions can be used to estimate the location and type of the source, simultaneously. The advantage of using Euler deconvolution of invariants compared to other methods that use invariants is that the only parameters involved in location approximation are invariants and their derivatives. Therefore, it is completely independent of the orientation of the coordinate system as well as having little sensitivity to random noise. In this study, the model is tested on synthetic models with and without noise. Finally, application of the method has been demonstrated on measured gravity gradient tensor data set from the Blatchford Lake area, Southeast of Yellowknife, Northern Canada.
    Keywords: gravity gradient tensor, Eigenvalues, Rotational invariant
  • Mehdi Torabi, Morteza Fattahi * Pages 50-67
    Over the past few years, different theories (piezoelectric, positive holes, friction-vaporization, exo-electron emission, tribo- or fracture electrification) have been presented for the interpretation of earthquake lights. Although these theories can interpret earthquake luminous, each suffer from particular problems. There are also ambiguities and questions about the location of the light, the number of light created in an earthquake, the relationship between light and lithology and the different light spectrum. In addition, the proposed theories could not interpret all the observed light (co-seismic and pre-seismic luminous), and it seems that more than one theory is needed to justify the lights. The relationship of the EQLs to active tectonic boundaries suggests all the earthquakes in which light has been seen are located on the active tectonic boundaries and the stress for producing lights should be at its maximum. This study shows that a new theory is needed. A theory that can, above all, explain the relation of light (spectrum and intensity) to lithology, the amount of stress, and active tectonic areas.
    Keywords: earthquake lights, co-seismic, tectonic boundaries, Lithology, spectrum
  • Abdollah Sohrabi, Bidar *, Masoud Amel, Sakhi, Arash Shareghi, Shahram Maghami Pages 68-81
    There are valuable investigations on the amplification effects of the topography on the seismic response in the frequency domain; however, a question is that how one can estimate the amplification of time domain peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD) over the topographic structures. In this study, the numerical approach has been used for the evaluation of time domain peak ground motion parameters amplification on a two-dimensional Gaussian-shaped hill in a typical rocky medium. Five normalized geometries, as well as the twelve normalized vertical incident motions, have been used. Incident motions are SV wave of Ricker type. Time domain responses of displacements, velocities, and accelerations have been calculated and analyzed in selected points of the hills. Tabulated results illustrate a significant role of geometry on the patterns of the amplification, and that almost the top of the hill amplifies and the hill toe de-amplifies the motion. Meanwhile, the rate of the amplification and de-amplification generally depends on the predominant period of the incident motion. Comparison of the amplification of PGA, PGV, and PGD values with the Fourier amplification curves showed that, in general, there is a well-matched correlation between them; however, the time domain amplifications of PGA, PGV, and PGD values have a gentler variation with the predominant period of the motion. It seems that one can give a reliable estimation of time domain amplification of PGA, PGV, and PGD values by using averaged Fourier amplifications over the suitable range of frequencies around the predominant period of the input motion.
    Keywords: Topographic effect, Peak ground motion parameters, Amplification, Two-dimensional hills
  • Ehsan Rezaie Faramani, Riahi Mohammad Ali, Hosein Hashemi * Pages 82-94
    Sequence stratigraphy is a key step in interpretation of the seismic reflection data. It was originally developed by seismic specialists, and then the usage of high-resolution well logs and core data was taken into consideration in its implementation. The current paper aims in performing sequence stratigraphy using three-dimensional seismic data, well logs (gamma ray, sonic, porosity, density, water saturation and resistivity) on Hendijan oil field located in the northwest part of Persian Gulf. , Depth interval of the study that covered from Asmari formation to Kajhdumi formation was determined by using well markers. Based on the depositional sequence model that consists of four systems tracts and with the help of Wheeler diagram, observed patterns have been used in seismic reflection terminations to identify sequence boundaries, systems tracts and internal stratigraphic surfaces in the sequences. Additionally, well logs were interpreted for two objectives. Firstly, variation patterns of well logs were used to validate sequences, their components and internal sequence stratigraphic surfaces. Secondly, the well log data was used for characterization of systems tracts with the log values.
    This paper addresses the constraints patterns for such stratigraphic problems in seismic interpretation with the aim of achieving better chrono-stratigraphic reasoning system with previous studies in Iran.
    Keywords: Sequence Stratigraphy, Depositional Sequence, systems tracts, wheeler diagram, and well log