Journal of the Earth and Space Physics
Year:2000 | Volume:26 | Issue:2|Papers Count:9

The ellipsoidal Stokes boundary-value problem is used to compute the geoidal heights. The low degree part of the geoidal heights can be represented more accurately by global geopotential models. So the disturbing potential is splitted into a low-degree reference potential and a higher degree potential. To compute the low-degree part, the global geopotential model is used and for the high-degree part, the ellipsoidal Stokes integral is used. I present an effective method to remove the singularity of the spheroidal and spheroidal ellipsoidal Stokes functions around the computational point. Finally, the numerical results of solving the spheroidal ellipsoidal Stokes integral are shown.

Ground vibration is a serious outcome of open pit mine blastings. The effect of the azimuth of measuring point to the blasted block, the effect of starting point and the direction of blast movement on the vibration of the surrounding area of the blasted block are considered. In Sarcheshmeh Copper Mine in SE Iran, seismic waves generated by 14 blasts have been recorded by 6-8 digital seismographs with three component seismometers. Seismic data from vertical, tangential and radial component seismograms were processed and analyzed in the frequency and time domains. By the convolution of seismograms related to one single blasthole with the time series corresponding to two double blastholes we simulated seismograms for two double blastholes with delay time of 25 and 65 msec. Results of the seismogram simulation were compared with seismic real data recorded by 3-C seismometer from double blastholes. Thereafter, the accuracy of the method was confirmed. Then, we simulated seismograms related to several multi-row blastholes with various delays between holes and rows. Quantifying the effect of location and azimuth of the measuring point as well as the direction of blast movement on simulation of seismograms, the impact of them on the ground vibration was studied. It was shown that the minimum ground vibration is in a direction with the azimuth of 180-225° with the free surface of the blasted block.

A method of three-dimensional ray tracing and model parameterization is presented. The method is intended for propagation media with a laterally varying velocity and thickness. Developed algorithm in this study (FAIT-3D) is based on the shooting ray tracing technique and solves 3-D Eikonal equations using finite difference methods. While rays are being traced, the traveltimes and their partial derivatives with respect to parameters of the model grids are calculated. In order to evaluate the adequacy and robustness of the algorithm, two synthetic models with several in-line profiles were used. The results surpassed our expectations in several ways.

Magnitude has played a particular role in the realistic description of global seismicity. Most studies in earthquake seismology use magnitude data as a guide to the strength of an earthquake. So biases in magnitude estimates, caused by any effect, directly affect the result of any study in which magnitude data is used. In this study, efficiency of using different formulae and depth-distance calibration terms are examined. Applications of the MsR-P formula and new depth-distance terms to the ISC dataset, show that the estimated Ms and mb values are independent of distance, and provide unbiased estimates of Ms and mb in comparison with commonly-used Prague formula and Gutenberg-Richter terms. Comparison of standard deviation of Ms values for single events using the MsR-P and MsPrague formulae show that the MsR-P standard deviations are consistently smaller than those of Prague formula. Also standard deviations of estimated mb values using the new depth-distance terms are smaller than standard deviations of estimated values using Gutenberg-Richter terms. Estimated Ms and mb values using MsR-P formula and the new depth-distance terms reduce overlap in Ms:mb criterion for underground explosions and earthquakes. The study reported here confirms the need to modify the formula for Ms calculation and depth-distance correction terms for mb calculation, which are used by global agencies such as ISC and NEIC.

In this paper an attempt was made to introduce the procedure of thermal data logging in shallow wells and to show the correlation between the thermal anomaly and shallow tectonic events in the study area. In this context thermal well logging data of the Salman Farsi dam site is chosen. The dam site area is located in south central part of Zagros Mountain Near To Shiraz, Iran. Thermal diagrams versus depth were performed and preliminary considerations were made using least squares method. This study showed a considerable thermal anomaly at the dam site. In this stage the Fourier thermal function was used to determine the thermal gradient of the anomalous zone. Indications of geological informations revealed that the temperature anomaly may be attributed to hot ground water impressed by a local minor fault.

In this paper, the velocity values of shear and compressional elastic waves of Phyllite limestone samples obtained both theoretically and practically are compared. These rock samples were performed in cubic shape. At the room pressure and temperature, the velocity values for these samples were measured using the first arrival times of elastic waves along the mentioned samples. The frequency of compressional waves was 63 kHz and that for shear waves was 33 kHz. The velocity values of compressional and shear waves for different incident angles such as 0, 30, 45, 60 and 90 degress between the receiver and the transducer were measured. In the theoretical stage, the crack density and dynamically Lama's constants were computed using Budiansky and O'Connell (1974) theory. Then, the theoretical velocity values of the same samples were calculated based on Hudson (1980) theory. The obtained results showed that a good correlation exists between the calculated and the measured data for the samples with low crack density. While for the samples with a high crack density the correlation is poor when the incident angles were at 30, 45 and 60 degrees. This difference between theory and measurements might be attributed to the presence of inclusions and inhomogeneity in the rock samples.

For studying Gold-Arsenic mineralisation in Shirmard region, we have used aeromagnetic data. After processing the data and applying regional correction, we plotted the total and residual magnetic maps of th~ region. These maps with respect to the state of magnetic anomaly contours, specify the existence of a fault in the north of region as well as magnetic bodies in the surface of the region. For obtaining more information. different filters such as downward continuation, upward continuation, vertical derivative and reduction to the magnetic pole have been applied for determining the location of deep and shallow magnetic bodies in the region. Then we determined the average depth of shallow and deep bodies in the region by forming power density spectrum data. The existence of great aeromagnetic anomaly in this region, variety of mineralisation and para genesis of Zarshoran and Aghdareh mineral regions, proves the necessity of economical geology studies. Composed and simultaneous study of this region with respect to the observed correlation in aeromagnetic interpretation between this region and dispersed mineral signs in around, has been considered as studical model. In this search we have tried to offer a correct and rational model by using accurate software and desert examinations simultaneously.

Darband and Golabdareh watersheds are located in the north of Tehran with a combined area of 33 km2. In July 1987, they exprienced a sever flood that caused immense damages to the northern part of Tehran and claimed number of lives. The objective of the present study is to investigate the said flood as well as flood frequency in the region. Unfortunately, the existing dischargegauging stations have short records and there are not enough measurements from past floods. Because of the above problem, rainfall-runoff simulation was identified as the appropriate way to analyze flood peaks and hydrograph. Among the different models for this kind of simulation, HEC1, HYMO, rational and matrix models were selected for the purposed simulations. The results show better performance of matrix model. For the flood of July 1987, this model estimated peak flood equal to 356 m3/s.

This paper is focused on the effect of the severest recorded EI-Nino on Iran climatic situation. The effect of the 1982-83 EI-Nino on temperature and precipitation is very considerable. The average temperature during the period is much lower than normal and the precipitation is considerably event will help the prediction of the climatic situation of our country. The investigation shows high negative temperature anomaly and positive precipitation onomaly during the period. Also an annual lag in minimum temperature and maximum precipitation can be seen clearly, although the lag in maximum temperature is not so considerable. The contrast of the winter monsoon stream and south or southwestern stream because of the event produce high gradients of isobars on Iran. The strengthening and shifting of monsoon toward Iran could be seen in the summer monsoon which results in warmer summers during the period.