Dr Sasan Motaghed, Dr Marzieh Shamsizadeh, Dr Nasrolla Eftekhari,
Volume 18, Issue 3 (12-2024)
Abstract
In this study, we present the Seismic Hazard Possibility Space (SHPS) for the city of Ahvaz. To achieve this, we applied the intuitionistic fuzzy method to weigh the logic tree used in the hazard analysis and constructed the SHPS based on expert opinions regarding the degrees of membership and non-membership. Hazard disaggregation was performed by through the concept of intuitionistic fuzzy sets, leading to the development of an intuitionistic fuzzy of an Intuitionistic Fuzzy Logic Tree (IFLT). The SHPS includes both the degree of membership and non-membership for pathways contributing to hazard generation. The SHPS illustrates the acceptance, non-acceptance, and ambiguity associated with potential hazard values from an expert perspective, thus assisting analysts in selecting appropriate hazard values. According to the numerical results of our analysis in the Ahvaz region, the seismic hazard is located in an uncertainty (unacceptability) zone, indicating that experts have low confidence in the results of the probabilistic seismic hazard analysis (PSHA) for Ahvaz. In addition, the hazard is characterized by an "unconfident zone". This finding indicates that experts are fairly confident in the results of the analysis for Ahvaz. This finding implies that the models and parameters used in the PSHA for this region are not accepted by experts, and further efforts are needed to identify or develop appropriate models and accurate parameters specific to the area. In conclusion, this research demonstrates how intuitionistic fuzzy sets can be used to construct SHPS, providing a novel framework for quantifying uncertainty and expert opinion in hazard assessment.
Mr. Ehsan Pegah, Mr. Behrang Feiz Aghaei,
Volume 18, Issue 3 (12-2024)
Abstract
Random noise reduction has always been one of the most important issues in seismic data processing. This study investigates one of the most effective random noise reduction methods, the 2D multi-stage median filter. This filter is applied to seismic data by applying a series of 1D median filters in different directions and then selecting the output value corresponding to the center of the 2D window. By applying a 2D multi-stage median filter to both synthetic and real data, it is shown that the filter can effectively attenuate random spike-like noise in both pre-stack and post-stack data. Similarly, based on spectral analysis, it is shown that this filter does a good job of reducing the level of high frequency random noise in both synthetic and real data. In this study, a 2D median filter is applied to synthetic data containing random noise with a density of 10%. Since increasing the filter length can damage useful signals in addition to attenuating random noise, it is important to specify an appropriate filter length. For synthetic data, the error ratio plot shows that a filter length of 9 points is appropriate for the first stage. In the second stage, a 2D median filter with a length of 7 points was applied to the output of the first stage filter. The effect of this filter on random noise suppression can then be observed by spectral analysis. In addition, median filters of 7 points and 5 points were applied to the pre-stack and post-stack real data, respectively. The effect and efficiency of this filter is assessed by examining the resulting difference plots, sections and spectral analysis.
Ehsan Pegah,
Volume 19, Issue 1 (6-2025)
Abstract
Accurately quantifying the anisotropic elastic parameters of in situ soils is essential for many geotechnical and geological engineering studies. This research introduces an innovative geophysical field technique for assessing these parameters in situ by utilizing the directional variations of P-wave and S-wave velocities. Assuming cross-anisotropy in the soil layers at the test location, it was shown that P- and S-wave propagation velocities along different orientations and planes can be effectively measured through a combination of seismic refraction and downhole surveys. The refraction data were analyzed using Seismic Refraction Tomography (SRT), Multichannel Analysis of Surface Rayleigh Waves (MASW), and Multichannel Analysis of Love Waves (MALW) to estimate the horizontal P-wave velocity (VPH), vertical S-wave velocity (VSV), and horizontal S-wave velocity (VSH), respectively.Moreover, the vertical and oblique P-wave velocities (VPV and VPθ) were identified by evaluating the travel times and distances of wave signals obtained from downhole tests. These velocity measurements were then incorporated into advanced equations formulated from elastic wave propagation theory, facilitating the computation of elastic parameters at the site. To evaluate the accuracy and efficiency of the proposed approach, the obtained results were compared with corresponding laboratory measurements, revealing a satisfactory level of agreement between the two datasets. The proposed methodology offers a practical means for in situ assessment of cross-anisotropic elastic properties in near-surface geomaterials using field-based seismic techniques.
Maedeh Roshan Liarajdameh, Milad Davari Sarem,
Volume 19, Issue 2 (10-2025)
Abstract
Iran, due to its location between two active tectonic plates, has always been exposed to numerous earthquakes. The occurrence of more than 100 severe earthquakes in the past century indicates the country’s high level of vulnerability to this natural hazard. The aim of this research is to analyze the seismicity and assess the earthquake hazard in Shahid Rajaei Port, as the largest commercial port in Iran (located at the intersection of the North-South transit corridor), which will be a fundamental step in enhancing the resilience and sustainability of the vital infrastructures in this region. In this study, all seismic events occurring within a 200-kilometer radius of the site were used, along with the Knopoff and Ez-Frisk software. The statistical analysis of historical and instrumental earthquakes indicates a high level of seismicity in the region, characterized by moderate-magnitude earthquakes with short return periods, such that earthquakes with magnitudes between four and five on the Richter scale constitute a larger share. The probabilistic hazard assessment estimated the maximum horizontal and vertical accelerations as 0.385 and 0.290 (g), respectively. Additionally, the site response spectrum was prepared based on the accelerographs of the Tabas earthquake and the isoacceleration maps of the study area, generated at intervals of 1.0 degrees in both latitude and longitude directions. The results showed that the study area has a seismic hazard of 0.85 (g), which is higher than the standard values specified in Iran’s Code 2800, placing it within the very high relative hazard zone. Therefore, implementing risk-based approaches in infrastructure development helps optimize port design and reduce earthquake-related damages.
