Tectonics
Khatoun Pirdadi; Maryam Agh-Atabai; Attieh Eshaghi
Abstract
The 2017 Ezgeleh earthquake (Mw: 7.3), which occurred in the northwest of the Zagros, was followed by many aftershocks. The histogram of the monthly rate of aftershocks shows that, except for the first few months, the aftershock sequence did not follow the Omori law. Therefore, it is necessary to use ...
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The 2017 Ezgeleh earthquake (Mw: 7.3), which occurred in the northwest of the Zagros, was followed by many aftershocks. The histogram of the monthly rate of aftershocks shows that, except for the first few months, the aftershock sequence did not follow the Omori law. Therefore, it is necessary to use more complex methods to investigate the aftershock sequence. In this research, the temporal multifractal method was used. The obtained results show that the temporal pattern of aftershocks has two short and long-scaling ranges. It seems that short and long ranges are related to the distribution of aftershocks within smaller clusters and the pattern of clusters in the aftershock sequence, respectively. These result showed that the pattern in the longer range is more heterogeneous than the shorter one. On the other hand, by removing the smaller aftershocks, the heterogeneity increases. It seems that the occurrence of several more significant aftershocks with a magnitude of more than 5 has caused an increase in the heterogeneity of the temporal pattern of the aftershock sequence. The results also show that the degree of inhomogeneity of the occurrence time of aftershocks is related to the spatial distribution pattern of aftershocks.
Tectonics
Fereshteh Jafari-Hajati; Maryam Agh-Atabai; Majid Nemati; Ali Biglari-Fadafan
Abstract
In this research, to understand the present-day tectonic situation of Gorgan-plain in the east of the South Caspian basin, the tectonic stress regime of this area and its adjacent areas was estimated using the inversion of the data of the earthquake focal mechanisms. For this aim, in addition to analyzing ...
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In this research, to understand the present-day tectonic situation of Gorgan-plain in the east of the South Caspian basin, the tectonic stress regime of this area and its adjacent areas was estimated using the inversion of the data of the earthquake focal mechanisms. For this aim, in addition to analyzing focal mechanisms solved by different sources, the focal mechanisms were solved for several earthquakes with appropriate and sufficient information. The results indicate the presence of various mechanisms, including thrust, normal, and strike-slip, and as a result, various orientations of kinematic P and T axes, which can indicate the complexity of the region. By analyzing the earthquakes with a minimum magnitude of 4 in the Gorgan-plain, the Kopeh-Dagh in the east of the plain, and the entire eastern region of the South Caspian, a compression regime with a NNW-SSE trend was obtained. However, by analyzing all of the earthquakes (smaller and larger earthquakes) in the Gorgan-plain, a strike-slip regime was obtained, in which the trend of the P and T axes were calculated NE-SW and NW-SE, respectively. The results indicate a local strike-slip regime in addition to the regional compressional regime in the region.
A. Zamani; M. Agh-Atabai
Abstract
The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was ...
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The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was followed by relatively large number of aftershocks. In this research, the aftershock sequence of this earthquake has been studied by measuring quantitative indices of coefficient of variations (CV), the exponent of the power spectral density function, and the generalized multifractal dimensions. The results reveal the presence of fractal structure in the temporal and spatial distribution of aftershock sequence. The multifractal behavior of the aftershock sequence indicates the clustering of the earthquake activity and the degree of the heterogeneity in the seismotectonic and geodynamic processes in the focal region. The results show that the multifractal dimensions of the aftershock sequence decreases and the multifractal dimensions of aftershock epicenters increases with time. It seems that these changes in the multifractal dimensions are related to the activity of secondary and sympathetic faults and changes in the tectonic stress regime of the region. The results also indicate that the multifractal method rather than monofractal approaches is a powerful tool for quantitative analysis of aftershock process's clustering behavior.
