Seismotectonic Characteristics of the Faults in the S, W Lut Block by Structural Maturity and Fractal Dimension

Document Type : Articles

Authors

1 Seismological Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran

2 Geological Survey and Mineral Explorations of Iran, Tehran, Iran

Abstract

The study area is located in the W-S Lut block. Eleven destructive earthquakes, from 1977 to 2012, were accompanied by about 185 km of the surface rupture in the South and Southwest of the Lut block. These earthquakes have resulted in ~44,700 human fatalities, ~36,646 injured and more than 100,000 homeless. In the western and southern margins of the Lut Block, there is a complete absence of historical records of earthquakes up until ~160 years ago. This lack of records may be resulted from the isolation of the area due to proximity to deserts (Ambraseys and Melville, 2005; Berberian, 2005). Nevertheless, some historical earthquakes for the pre-1900 period are reported (e.g. Berberian, 1977; Ambraseys et al., 1979; Berberian et al., 1979; Ambraseys and Melville, 2005). There is no reliable estimation of the seismotectonic characteristic in this region; therefore, the seismic hazard assessment is not accurate enough. It is important that the seismicity of the area and its temporal and spatial variations are viewed as snapshots of the ongoing tectonic activities. Therefore, identification of the structural maturity and fractal dimension may provide complementary deductions for more realistic analysis and interpretation of the observations.
We investigated a number of faults in this area that have high potential for generating destructive earthquakes. The faulting patterns appear to preserve different stages of fault development. We investigated the distribution of active faults and the role that they play in accommodating tectonic strain in the SW-Lut.
For interpretation of structural maturity, we used fault segmentation, rupture length, displacement on the fault surface and pattern of repetition of the earthquake event. Based on the results of this study, the Kuhbanan fault is immature, the bam fault is middle until immature and Gowk, Lalehzar, and Kahourak are mature.
For the fractal analysis and the maturity of the fault zones in the area, we used fractal dimension. Based on the calculations, the fractal dimension of the Kuhbanan fault and its southern branches, Bam, Kahourak, Faryab, Chahmazrae (Esfandaqeh) and Gowk faults are less than the other faults in the study area. Along these faults, the focal mechanism of the earthquakes are more focused. Inner edge of the Lut block, the fractal dimension are increasing. This increase show high distribution of stress in this area. The dispersion of the stress field decreased the amount of stress and seismic activity in this area.
The fractal dimension of the Nayband fault system (1.56-1.72) and West Sabzevaran fault (1.52-1.68) reduce from north to south and Gowk fault (5.15-1.68) increase from north to south. Therefore, the southern part of the Nayband and West Sabzevaran faults and the northern parts of the Gowk fault are immature. These area have serious risk for the area.
Based on the results of structural maturity and fractal dimensions, Kuhbanan, Bam, Kahourak, Gowk, Lalehzar, Faryab and Chahmazrae (Esfandaqeh) faults will create high risk of seismicity.
References

Ambraseys, N.N., Arsovski, M., and Moinfar, A.A. (1979) The Gisk Earthquake of 19 December 1977 and the Seismicity of the Kuhbanan Fault-Zone. UNESCO.
Ambraseys, N.N. and Melville, C.P. (2005) A History of Persian Earthquakes. Cambridge University Press.

Berberian, M. (1977) Contribution to the seismotectonics of Iran (Part II-III). In: Commemoration of the 50th Anniversary of the Pahlavi Dynasty.


Berberian, M., Asudeh, I., and Arshadi, S. (1979) Surface rupture and mechanism of the Bob-Tangol (southeastern Iran) earthquake of 19 December 1977. Earth Planet Sci. Lett., 42(3), 456e462.


Berberian, M. (2005) The 2003 Bam urban earthquake: a predictable seismotectonic pattern along the western margin of the rigid Lut block, southeast Iran. Earthq. Spectra, 21(S1), 35e99, https://doi.org/10.1193/1.2127909.

Keywords

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History

  • Receive Date: 23 June 2018
  • Revise Date: 27 February 2021
  • Accept Date: 26 December 2020

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