IRANIAN JOURNAL OF GEOPHYSICS
Year:2008 | Volume:1 | Issue:1|Papers Count:9

In this paper, the effect of structural discontinuities on blast- induced wave propagation in a Plexiglass media is investigated by using UDEC Code which is a distinct element method based. The stress wave resulting from the explosion of a cylindrical charge is simulated by a triangular pulse which is the result of a dynamic pressure equivalent to 11GPa. This pressure is applied to the blast hole wall with 5.08 mm diameter as a uniform load. Dynamic pressure on blast hole is considered to be radial and is distributed uniformly. Peak particle displacement, peak particle velocity, applied stress, reflection and transition coefficients are estimated for elastic media behavior. The obtained numerical results are compared against experimental results of Fordyce et al, (1993). A good agreement between numerical and experimental results is achieved.

Typical VLF data exhibit considerable 2D effects and 2D inversion offers several advantages when applied to profiles of VLF data. First it provides a quantitative estimate of the basement conductivities away from conductors. Secondly the relation between real and imaginary parts of the tipper vector provides information about the depth of the major conductors giving rise to the anomalies. In this paper, a synthetic model of a vertical contact and a profile of airborne VLF data are discussed.

In this study, the frequency dependence of P and S wave’s attenuation are determined in terms of Q-1p and Q-1s in Mashhad area. The local seismic data used in this analysis are come from 10 seismic stations, installed in the area during this study. The extended coda normalization method has been used in this research. The analysis shows the frequency dependence of attenuation in Mashhad area. The Q-1p decrease from 0.01258±0.005034 at 1.5 Hz to 0.000863±0.000414at 24.0 Hz and Q-1s decrease from 0.008019±0.004359 at 1.5 Hz to 0.000352±0.000314 at 24.0 Hz. Using the regression methods we have fined the following relations:Q-1p (f) = (0.0162±0.0106) f (-0.9198±0.2446) Q-1s (f) = (0.0136±0.0110) f (-1.1868±0.3976)

Seismic Facies Analysis (SFA) is a powerful technique to define the variations of the seismic character of traces at reservoir level, in connection with possible variations of reservoir property which is essential for estimating reserves and planning production operations. In this study we try to integrate 3D seismic data and effective porosity logs to predict lateral variations of porosity in Mishrif reservoir (A common oil reservoir in Persian Gulf).Both supervised and unsupervised seismic facies analyses have been performed at reservoir level. The results are convergent and consistent with petrophysical well data as well as predicted mean porosity map from previous study, and allow defining areas with low and high mean porosity values. The unsupervised analysis not only confirms the results of the supervised method but also gives more detailed lateral distribution of the seismic facies. The areas with low mean porosity values are mainly located in the southern part of the study area, while the areas with high mean porosity values are located in the northern part with an extension to the west of the study area.

In this paper, we attempt to compare the dynamical structure of modons, as solutions for the quasi-geostrophic potential vorticity equation in geophysical fluids and blockings. To do this study, a blocking event which was observed in December2002and had the same structure with equivalent barotropic modon, was chosen. Then, the relevant synoptic maps in different pressure levels as well as quasi-geostrophic potential vorticity (q) and stream function (y) maps in 300hPa were prepared. The results show the association between the appearance of a low cutoff value of q in quasi-geostrophic potential vorticity maps at 300hPa levels and the intense high anomaly in the 500hPa geopotential height maps. In addition, the scatter diagram of q against y clearly shows the various dynamical features of the blocking in both the blocked and non-blocked regions. Comparison of this diagram and the theoretical modons diagram indicates the similarity between the structure of atmospheric blocking in westerly currents and theoretical modons.

Gravimetry is an effective and almost inexpensive approach to assess the depth to bedrock in sedimentary basins. In this research a gravity data sets located in south part of Zagros has been applied. The sedimentary deposits covered the top of a syncline which is located between two anticlines. An iterative gravity inversion method (Jachens and Moring, 1990) has been applied to determine the depth of sedimentary deposits in the region. In order to test the accuracy and practicability of this method both 2dimensional and 3dimensional synthesizeddata has been applied. For determining the surface density and density-based zoning of the region aNettelton Analysis has been used. Geological andgeomorphological evidences almost confirm the determined depth results.

Earthquake location is an inverse problem that usually involves inverting the imperfect arrival time readings for the earthquake parameters. When the forward model (a method for computing arrival times) is derived then the final solution will be obtained based on a misfit criterion that minimizes the discrepancy between the calculated and measured data. The event location uncertainty is caused by: the errors in the arrival times of the picked phases, misidentification of seismic phases, and the errors in the travel-time model used in the location process. The event mislocation induced by these sources is affected by the number and configuration of the stations that record the events. In this paper the expected errors for the Tehran digital seismic network has been simulated, considering two different velocity models. It has been found that the expected error along the longitude of the network is less than the expected error along its latitude. Meanwhile epicentral expected error seems to be high. So it is proposed to consider this method results not only for the Tehran network but also for other present and future seismic networks.

Radar method (GPR) is one of the electromagnetic methods to detect shallow depth of underground layers. Sarab E Ghanbar region which is situated at south of Kermanshah city is at thrusted Zagros region. At this region limestone with different ages are adjacent to radiolarites sediments. Due to fractured Limestone and low permeability of radiolarites, study of radiolarites is important as the latter acts as a dam to water flow from limestone. 100MHZ unshielded antenna has been used to a small part of radiolarites to detect fractured and deformed layers. Depth of penetration of radar waves is lm and their velocity is 0.069m/ns. Radargrams show the main fracture at 8m from the first point of the measurements. Deformed layers are located at different horizontal distances at maximum depth of 1.5m. Some radargrams show an anticline at 22m which is in agreement with field observation.