Journal of the Earth and Space Physics
Year:2006 | Volume:32 | Issue:2|Papers Count:13

Determining seismic parameters especially estimating magnitude with enough precision has an important role in the explanation of the seismicity of a region. However, the method of magnitude determination based on an empirical relation, relates to the released energy in each earthquake. Magnitude scale is widely used because it is the proper method for estimating the size of the earthquake. In this study, to evaluate the reported magnitude value for Kojor-Baladeh earthquake which occurred on 28th May 2004, the value of magnitude was determined by using recorded seismograms in seismic stations then compared with that value reported by IGUT. The result of the investigation shows that the reported magnitude, about 0.6 magnitude unit was underestimated. This study shows that the main factor in this underestimation is the software which is used to process recorded data. Many researchers have shown that it is better to estimate local magnitude by using measurements on horizontal components. This study also showed that in the Kojor-Baladeh earthquake the resultant horizontal amplitude of Lg wave on horizontal components is about twice the amplitude on vertical component.

This paper detects the main features of the conductivity structures in the exploited geothermal field of Travale in Italy, where a detailed study was conducted using Magnetotelluric (MT) data in 2004. In this area, the long period natural-field MT method proved very useful for subsurface mapping purpose so that deep resistivity structures were determined properly. Using 1D inversion schemes, MT data were processed and modeled. To have the best possible interpretation all modes of data were examined.The resistivity model obtained from MT data is consistent with the geological model of the Travale region down to five kilometers. Analysis of the new MT data-set suggests signatures of a deep geothermal reservoir in the area. The conductive zones which are recognized in the resistive basement in many sites can clearly be interpreted as the flow of the fluids in the faults and fractures of the metamorphic rocks.

Hydraulic parameters are needed to characterize the Tehran plain aquifer, Determination of these parameters by pumping test is expensive and laborious. In order to estimate aquifer permeability and transmissibility, the resistivity of the aquifer and its water content are needed. In this research fourteen pumping test experiments were considered for analysis. The relationship between hydraulic parameters and formation factor, normalised resistivity and normalized transverse electrical resistance of the aquifer are linear.

Trend surface analysis is a type of multiple regressions where point coordinates are independent variables and grade or thickness and ... can be dependent variables. In this method, we fit a suitable surface to major values. In this paper, we applied trend surface analysis to airborne geophysical data sets including the magnetic field intensity, resistivity (frequency=4600 Hz) and radioactivity (potassium counting). Results show the trend of these factors and their relations. Magnetic field intensity and resistivity have a similar trend despite the trend of Potassium counting. Finally, the ability of this method in interpreting the same data has been acknowledged.

The super compact finite difference method is used for integrating the conservation-law form of the shallow water equations in the beta plane. The second-order delta formulation of the trapezoidal time differencing scheme is used. The sixth-order super compact finite-difference method is applied to discretize the spatial factored form of the equations obtained using the ADI method. Because of the large aliasing error introduced by the super compact scheme, the application of a very selective low-pass filter, based on compact schemes, is introduced to overcome the error generated by the interaction of the nonlinear terms of the equations. The integral invariants of the shallow water equations, i.e., the total energy and potential enstrophy are well conserved during the numerical integration. This fact shows that the nonlinear structure of the equations is correctly modeled. The validation of the sixth-order super compact results are investigated by comparing them with the results of the fourth-order compact and second-order finite-difference schemes for different grid resolutions.

One of the transient variations is named geomagnetic bay, which looks like a map of an indentation in a coastline or Gaussian curve. This type of variation (and all variations) induces electric currents in the earth. The induced electric currents give rise in turn to an internal component of the magnetic variations observed at the surface. The ratio of the parts of the magnetic field of internal and external origin is a measure of the response, and is dependent on both the external current system and the distribution of the electrical conductivity within the earth. Using this method, the electrical conductivity of the earth can be determined for various depths according to the period of the magnetic variations. The duration of bay can be from a few minutes to a few hours. The bays generally occur on solar quiet days accompanied with Pi1 and Pi2 micropulsations. The bays are two-stage events; the early stage is the trigger bay and the second is the main bay. In this paper, a statistical study of bays recorded at Tehran geomagnetic observatory for the period of 1971-80 is made according to the time of their occurrence, intensity and direction. We have also taken into consideration the geomagnetic seasons. Maximum numbers of bays occur at midnight with moderate intensity and positive direction. Most of the bays take place during the Equinox and December solstice. Return currents are predominant current system. The delay time between the onsets of the two stages lie the range of 10-30 minutes. The relation between the numbers of the sunspots and the bays is inversely proportional

In marine seismic surveys amplitudes, frequency contents and travel times of seismic waves are influenced significantly by elastic and physical properties of .sea-bed sediments. Therefore, investigation of elastic properties of propagation medium at the bottom of the sea floor is worth while in marine seismic studies.In this paper refraction arrival times are analyzed to estimate the velocity structure and anisotropic parameters of sea-bed sediments using a vertical-cable (VC) configuration. Two sets of synthetic seismic data from two distinct earth models were used to evaluate the influence of dip and anisotropy of layers on propagation of seismic waves. In the first set of data, for a constant value of anisotropy, the values of 00, 50 and 100 were assigned to dip in order to evaluate the influences of dip. However, in the second set of models, we kept the dip constant and varied the P-wave anisotropy strength of the medium to examine the sensitivity of ray-slowness to anisotropy. All above mentioned analyses were done on synthetic P-wave VC seismic records, which were obtained by solving of eikonal equation using finite-difference method. Our result indicated the usefulness of the VC acquisition method for determination of real dip (b), dip azimuth jd azimuth of symmetry axis with respect to the X-axis ja and anisotropic parameters (v P0, e) of the saturated sea-bed sediments.

In this paper, the applicability of Euler's homogenous equation method in detecting gravity anomalies from gravity or microgravity data is addressed. The stability of Euler solutions with respect to the window size, window position and choice of the structural index value (defining the anomaly attenuation rate) is analyzed and demonstrated using synthetic microgravity data created for different anomaly models. The analysis reveals that the optimum window size required to obtain the best solutions is a function of the source depth. The horizontal location parameters can be determined correctly if the window is located in the region of high derivatives regardless the assigned structural index v. Meanwhile, depth solution is linearly dependent on the structural index and incorrect choice of structural index leads to significant error in the estimated depth.

Instability indices are some parameters that could be used to determine the instability of different parts of the atmosphere. These indices are used to forecast convective activities and are calculated using thermodynamic diagrams derived from radiosound data.In this work, some of the instability indices are calculated for the Esfahan area during a 12 year precipitation period (1991-2002). These indices are: precipitable water of cloud (PWC), Showalter index (SI), K index (KI) and convective available potential energy (CAPE). The precipitation data are obtained by averaging observations from Esfahan airport (east of Esfahan) and Najaf Abad (west of Esfahan) stations. A suitable threshold for convective cloud seeding decision has been estimated using the best fit diagram of the index. This threshold has been found to be 9mm for precipitable water of cloud, 2 degrees centigrade for Showalter index, 24 degrees centigrade for K index and 100J/kg for CAPE.The results confirm previous cloud physicists, findings that perceptible water of cloud is the best index to estimate precipitation amounts for the Esfahan area. In addition, high values of K index and CAPE with negative and low values of Showalter index may indicate intense precipitation.

This research is based on a numerical model for forecasting the three-dimensional behaviour of (sea) water motion due to the effect of a variable wind velocity. The results obtained are then analyzed and compared with observations.This model is based on the equations of motion temperature which are solved by finite difference assuming Dx, Dy as constants and Dz variable. The horizontal and vertical eddy viscosity and thennal diffusivity coefficients we used were in accordance with that of the Benet on Outario Lake (1977). Considering the Caspian Sea dimension in numerical model the Coriolis parameter used with D effects and the Boussinesq approximation have been used.For modeling the Caspian Sea the grid of the field was done as follows. At horizontal surface, grid size was extended to 10x10km and at perpendicular in 10 layers with varying thickness from surface to bed respectively as: 5, 10, 20, 30, 50, 100, 150, 200, 250, 500 and higher. The data of wind as velocity, direction and temperature of water related to 15th September 1995 at 6, 12 and 18 o'clock were obtained from synoptic station at the Caspian Sea side and the research marine of Haji Alief. The information concerning seaside wind was measured by the SPM method and was transferred to far seaside winds through interpolation and by using inverse square distance, position distribution of the wind velocity at the Caspian surface field was obtained.The model has been evaluated according to the reports and observations. Through studying the position of the current in different layers, the velocity in the cross section in the northern, southern and the middial layers, will be discussed. The current velocity throughout the whole field is different. The current velacity calculated ranges from 1.6 cm/s to 15cmls. The maximum velocity is observed in the middle, considering the maximum wind velocity 7m/s and wind stress tx=ty=0.06N/m-2. The results reveal the presence of circulation cells in the three areas in an anti clockwise sense. The circulation with depth is reduced. The results obtained through the numerical solution of the temperature equation have been compared with the observations. The predicted temperature change in different layers with depth shows good agreement with observations.

Since the radar images in addition to signal intensity measurement, carry the phase information, thus we can use phase information with InSAR method in studying earthquakes. Whereas most geodetic methods need to measure crust displacements repeatedly, InSAR in addition to covering all of the earth surface, doesn't need to repeat measurements. In this study, with InSAR surface displacements, the targets have been invented form Barn earthquake of Iran.With this method the magnitude of the Barn earthquake and its moment are 6/4 and 4/3 x 1018 respectively. In this study, we use 3 images of Envisat satellite for producing interferogram. Images are processed in Linux with Doris software. Finally, counting the fringes of interferogram, we can calculate the displacement and magnitude of Barn earthquake, and compare these results with other studies.

The parallel processing of artificial neural networks makes them suitable for hardware implementations; therefore, using artificial neural networks for seismic signal processing problems has the potential of greatly speeding up seismic data processing. In this paper, a commonly used neural networks, Hopfield neural network, is used to implement deconvolution. The deconvolution procedure decomposes into two sub processes: reflectivity locatin detection and reflectivity magnitude estimation. A Hopfield neural network is developed for each of subprocesses. The first neural network is developed to detect the reflectivity sequence. The second neural network is developed to determine the magnitudes of the detected reflections. These two neural networks are simulated for narrow-band wavelet, and the result is compared with that of using spiking deconvolution.With comparing the results, deconvolution of seismic data using Hopfield neural network: (1) unlike spiking deconvolution, is not sensitive to noise and (2) gives much better result than spiking deconvolution for a trace with noise.