Document Type : Original Research Paper

Author

• M Agh-Atabai

Assistant Professor, Department of Geology, Golestan University, Gorgan, Iran

Abstract

In this paper, the properties of temporal distribution of earthquakes in southeast Zagros were studied using multifractal methods. To describe the multifractal characteristics of the occurrence time of events, the generalized correlation dimensions D_q and the singularity spectrum f(α_q) were calculated for earthquake sequence with magnitudes equal to or larger than the completeness magnitude (M= 4.5). In order to investigation of the spatial variations of seismicity pattern, the study area is divided into the three subareas and the results of the analyses were compared to each other. The calculated multifractal spectra for all subareas indicate that the pattern of seismic activity in these regions is a heterogeneous multifractal phenomenon. However, the graphs of correlation integral functions of the studied subareas have clear differences. Except the transition zone on which there are three scaling ranges, the other subareas show two scaling ranges: short and long time scales. The properties of short time scale are controlled by the distributions of small earthquakes (e.g. aftershocks) in clusters, whereas the long time scale is related to the distribution of larger main earthquakes and the clusters related to them. In the graph of transition zone, the large time scale is divided into two different ranges with a characteristic break on about 3.6 years. This characteristic length means there is another kind of clusters (main shocks) rather than the small earthquake clusters. The graphs of recurrence time of earthquakes support these results and show the shorter recurrence time of events in the transition zone. In addition, the results show that the transition zone has a more heterogeneous multifractal pattern rather than its surroundings.

Keywords

• Earthquake
• Multifractal
• transition zone
• Asymmetry Factor
• Recurrence time