Journal of the Earth and Space Physics
Year:2002 | Volume:28 | Issue:1|Papers Count:9

In this study, the source parameters of the 1998 Fandoqa earthquake were investigated. The observed teleseismic. bodywaves of mainshock were modeled in order to obtain the source process. The information from field investigations and the result of locally recorded aftershock activity were considered as supplementary data. The source process fitted with a single source model having a strike-slip mechanism very similar to the result of CMT solution. Rupture during this earthquake initiated in the epicentral area and extended in a bilateral manner. The seismic moment from bodywaves was calculated to be M0=7.1×l025 dyne-cm and its effective stress drop was about 86 bar while its related dislocation was estimated to be 1.46 m.

During the last twenty years, heterogeneous freezing nucleation has been one of the important fields of study in meteorology, and, it has been of special interest to cloud physicists. However, despite much success in this field there remain numerous ambiguities in the ice nucleation process. Using both, cold plate and fishing line apparatus, the drop freezing rate due to heterogeneous nucleation has been studied at constant temperature and constant cooling on rain samples over Gilan (near the north coast of Iran) during the autumn and winter, 2000-2001. The immersion freezing nuclei concentrations obtained in cumuliform (14.31-20.44 m-3) and stratiform (11.9-13.8 m-3) clouds are in good agreement with the results of previous researchers as Vali (1994), Cooper and Lawson (1984), Rogers and Yau (1996). These are, however, much less than the amounts reported by various cloud seeding projects faced with over seeding problem. Therefore, Gilan area clouds have very good seeding potential. These results can provide valuable information about recognizing cloud systems in the experimental area, and let physicists predict the success of their cloud seeding program projects. Before carrying out any artificial cloud seeding project, it is necessary to do some laboratory experimental work to prevent unnecessary expense. These low-cost experiments, not only, decrease the economic coefficient of efficient cloud seeding projects, but also the danger of airplane accident inside the clouds.

A review of past work in the subject areas of latent heat release in extratropical cyclones, within the concept of the potential vorticity framework or "PV thinking" is presented. It is also aimed to assess to what extent the conventional baroclinic instability theory can be applied to extratropical cyclones involving intense latent heat release. The main results of the previous studies concerning the effect of latent heat release on extratropical cyclones dynamics can be divided into two categories, depending on whether the impact of the diabatically generated PV anomaly on the baroclinic dynamics was very weak or strong. In the weak cases, cyclogenesis is primarily driven by baroclinic dynamics, with latent heat release playing a secondary role. Latent heating influences the baroclinic dynamics as simply by superposing a positive PV anomaly near the cyclone center without significantly altering the PV structure elsewhere. On the other hand, a few studies reveal that latent heat release can enhance largely the cyclone intensity, particularly when the surface thermal gradients are weak and alter significantly the structure of upper-level PV and surface thermal anomalies. The low-level diabatically produced PV anomaly is able to substitute for the absent surface warm anomaly.

The researches carried out in recent years show that the total column ozone (TCO) could have significant diurnal variations caused by photochemical and synoptic factors. Using a ground-based Dobson ozone instrument and Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) data, this paper discusses the relationship between the daily total column ozone changes and the weather condition over Esfahan (32 37 N, 51 40 E) during 1997. To investigate the relationship between the daily TCO and synoptic conditions, 43 cases are discussed at which the daily ozone deviations are statistically significant. A relatively good agreement is found between the tropopause height and the daily TCO changes .In addition, the jet stream shift is shown to be a very important factor affecting the total column ozone in Esfahan, Iran. Weak or no relation was found between the daily TCO and other synoptic factors such as the type of fronts and daily surface pressure changes. The results can be employed qualitatively in a rough estimation of the daily TCO and the DV index forecast as well.

Researchers for predicting Peak Particle Velocity (PPV), form allowable vibration values, have presented different criteria and empirical relations. These relations are applicable mostly to the geological conditions, for which they are derived. In this paper, most common empirical relation for predicting PPV, resulting from blasting, for nearby structures in Gol-e-Gohar iron mine, are reviewed. 1I three-component seismograms from two blasts were recorded by the digital seismograph PDAS-100 and processed and analyzed by DADISP software. The most suitable empirical relation was selected, which is a power equation, based on square root of scaled distance.

In this paper, the results of the development of a three-dimensional model for simulating mesoscale phenomena in the mountainous coastal areas of Iran are presented briefly. .The model is suitable for studying atmospheric disturbances, which are generated by land-sea surface temperature contrasts as well as by mechanical lifting and thermal forcing due to mountains and their interactions. The model is hydrostatic with a sigma coordinate along the vertical and based on non-linear time-dependent primitive equations. Initialization in the model creates a uniform prevailing wind. Parameterizations of the vertical and horizontal transport of eddy fluxes are incorporated. It also incorporates a unique formulation associated with the horizontal gradients of geopotential and surface pressure in the momentum equations. With this modification, the fatal computational error due to the spurious imbalance between the two terms, especially in the case of high irregular mountains and/or steep slopes, may be avoided or minimized. In the field of microphysics, explicit formula for evaporation from cloud droplets when they are advected to the unsaturated adjacent area, are added. This addition may give more reliable treatment of evaporation through preventing spurious local sudden cooling of evaporation. First, the model was examined in a region with a bell-shaped mountain. Then, it was used to simulate wind field, cloud and precipitation for a smoothed real region, including part of the Caspian Sea, the complex Alborz Range and part of the central plateau. Since sufficient data for a realistic initialization were not obtained through the meteorological stations in the study area, the initial conditions were therefore assumed and defined as much in accordance with the available data in a specified day. As a consequence, output was inevitably based tightly on this initial condition.

In this article new empirical global depth-distance correction terms for body-wave magnitude are determined using the values of scalar moment Mo in the Harvard CMT Catalogue to calibrate P-wave amplitude-distance curves. Application of new depth-distance correction terms, obtained here, to the ISC dataset shows that estimated mb is independent of distance and focal depth, and provides unbiased estimate of mb, in comparison with other published depth-distance correction terms such as Gutenberg-Richter (1956), Veith-Clawson (1972), and Lilwall (1987). Using Gutenberg-Richter, Veith-Clawson, and Lilwall correction terms, mb for deep earthquakes is systematically underestimated by about 0.1-0.15, 0.3-0.5, and 0.1-0.2 magnitude units respectively. This observation is also a positive test of the hypothesis that a calibration with respect to M0 gives a better estimate of mb. Comparison of the standard deviation of mb values for single events using different depth-distance correction terms shows that the Gutenberg-Richter standard deviations are, on average, larger than those of Veith-Clawson, Lilwall, and this study.