Ramezan Ramezani Omali, Mehdi Saeidian, Naser Hafezimoghadas,
Volume 9, Issue 1 (6-2015)
Abstract
Determination of Faults activity rate is among the most important parameters of evaluating faulting hazards. In this paper, active faults on region of Shahid Rajai dam of Sari with radius 100 km based on fractal dimension of faulting and earthquake as well as evaluation of slip rate were classified and those Activity rate were assessed. In order to determine of fractal dimension of faulting and earthquake, Box-counting method was used. For estimate of slip rate beginning the seismicity parameters (a&b) of study area was estimation. Then these parameters were normalized for each fault. Based on the existing relationships and having a&b for each fault, the seismic moment of fault was calculated. Finally according to extant relations for evaluation of seismic moment rate, slip rate of each fault was determined and the faults of study area were classified accordingly. By grading based on fractal dimensions, the faults of North- Alborz, Damghan and Garmsar have been the most active faults in the study area during the last 100 years and according to evaluations of active rate of faulting and earthquake based on fractal dimensions, generally set in category BD and their activity approved. The faults with very low slip rate and with long return period of earthquake, are possible causes of occurrence large earthquakes (856 AD) Gomes and inducement fault namely Damghan Fault is an example of these faults. The faults of Astaneh, Rameh and Cheshmeh-ali have been low slip rate and thereupon be able to develop high seismic moment rate. According to earthquake events in privacy of New faults introduced (Khorram-abad, Majid,…), the high activity rate of these faults seem logical
Mohammad Sadegh Sharifi, Saeed Zarei, Seyed Reza Mansouri, Abdullah Hussaini,
Volume 19, Issue 4 (12-2025)
Abstract
The active tectonics of eastern Iran, resulting from the convergence of the Arabian and Eurasian plates and numerous active faults, has caused high stress concentration, as evidenced by major historical earthquakes such as those in Tabas (1978) and Bam (2003). This study aims to conduct a fractal analysis of seismicity parameters and investigate crustal stress heterogeneity in eastern Iran. To this end, an earthquake dataset of historical and instrumental events with Mw ≥ 4 (1900–2024) was compiled from the ISC and NEIC databases. After filtering and declustering, the data were analyzed using ZMAP and ArcGIS. The b-value (an indicator of stress level and the probability of large earthquakes), the D-value (the geometrical complexity of faulting), and the D/b ratio were calculated simultaneously and mapped spatially. The results show that the b-value ranges from 0.8 to 1.1, and the D-value ranges from approximately 1.6 to 2.3. Regions with low b-values and high D-values, especially along the Nehbandan and Dasht-e Bayaz faults, indicate high stress concentrations and an elevated likelihood of larger earthquakes. The total seismic moment of the cataloged earthquakes is estimated at 3.5×10²³ N·m, yielding an average annual seismic moment rate of 2.7×10¹⁶ N·m/yr (calculated by averaging over the available catalog years). The D/b ratio, regarded as an index of stored energy and stress heterogeneity, exceeds two in these zones and exhibits a strong correlation with areas of a high rate of seismic moment release. This pattern implies that an increase in fault geometrical complexity coupled with a decrease in the b-value signals the crust’s approach to the rupture threshold. Thus, by emphasizing the significance of the D/b ratio, the present findings offer a quantitative approach to mapping stress states, fault structures, and the potential for significant earthquakes in eastern Iran.
