Iranian Journal of Geophysics

Iranian Journal of Geophysics

Fractal nature of seismicity pattern prior to the 2022 Hormozgan Doublet earthquakes, southeast Iran

Document Type : Research Article

Authors
1 Associate Professor, Department of Geology, Faculty of Science, Golestan University, Iran
2 M.Sc. Student, Department of Geology, Faculty of Science, Golestan University, Iran
Abstract
One of the goals of seismicity pattern studies is to find a precursor pattern prior to large earthquakes with the aim of their prediction. Foreshocks, doughnut pattern and seismic quiescence are seismic patterns that can be used as predictors in the short-term, medium-term and long-term period before earthquakes event (Mogi, 1985; Scholz, 1988). Researchers have shown that seismic parameters shows significant changes before the occurrence of earthquakes (Bayrak et al., 2017).  Investigating temporal changes of seismicity fractal parameters is one of the ways to find seismic pattern in periods before large earthquakes. In this research, the seismicity pattern before the 2022 Hormozgan (west of Bandar-e Khmir) earthquakes have been investigated using fractal methods. These earthquakes with moment magnitude (Mw) of more than 6 occurred on a dense seismic zone with a northeast-southwest trend at the southeast end of the Zagros fold-thrust belt. In this article, to investigate the precursory pattern, temporal changes of seismicity fractal parameters, including b-value, fractal dimension of earthquake epicenters, De, and fractal dimension of earthquake occurrence times, Dt,  were studied in a 3.5-years period before 2022 Hormozgan earthquakes. The correlation integral method was used to calculate the spatial and temporal fractal dimensions (Grassberger and Procaccia, 1983). The data used in this research (a circular area centered on the epicenter of the first event with a radius of 60 km) was extracted from Iranian Seismological Center (IRSC). The completeness Magnitude, Mc, was calculated 2.9 using the frequency-Magnitude curve, therefore earthquakes smaller than 2.9 were excluded from catalogue for subsequent fractal calculations. In this article, a fixed window method with a length of one year and steps of three months was used to investigate the temporal changes of the seismicity pattern. For each of the windows, three parameters b-value, De and Dt were calculated and graphs of their temporal changes were drawn. The results showed that until 2021 (1.5 years before the target earthquake event), the fractal parameters show changes corresponding to the occurrence of numerous earthquake clusters in this time period. Between the years 2021 and 2022, the change trend of two parameters b-value and Dt has been relatively stable after a significant increase. Then, all three seismic parameters have shown a similar pattern (increasing value) in a period of several months before the main events. The monthly seismicity rate histogram and magnitude time graph show that the seismicity rate from the beginning of 2021 until the 2022 Hormozgan earthquakes is very low and the distribution of earthquakes is scattered in time. But the space-time diagram shows that several months before the occurrence of the main earthquakes, there is a period of seismic quiescence around the main earthquake and at the same time, the seismicity continued in the north of the epicenter. It seems that the significant temporal changes of seismicity fractal parameters before the main earthquakes are due to the seismic quiescence, which can be considered as medium-term precursor of the 2022 Hormozgan earthquakes.
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Agh-Atabai, M., Mirabedini M.S., 2013, Temporal variations of seismicity parameters in the Central Alborz, Iran. Acta Geophysica 62(3), 486–504.
 
Aki K., 1965, Maximum Likelihood Estimate of b in the Formula log10N=a-bM and Its Confidence Limits. Bulletin of Earthquake Research, 43, 237-239.
Ashkenazy Y., Ivanov P., Havlin S., Peng, C.K., Goldberger, A.L., Stanley, H.E., 2001, Magnitude & sign correlations in heartbeat fluctuations. Physical Review Letter, 86, 1900-1903.
Aubourg C., Smith B., Bakhtari H.R., Guya N., Eshraghi A., 2008 , Tertiary block rotations in the Fars Arc (Zagros, Iran). Geophysical Journal International, 173, 659-673.
Bak P., Tang C., 1989, Earthquakes as self-organized critical phenomena. Journal of Geophysical Research, 94, 15635–7.
Bayrak E., Yilmaz S.H., Bayrak Y., 2017, Temporal and spatial variations of Gutenberg-Richter parameter and fractal dimension in Western Anatolia, Turkey. Journal of Asian Earth Sciences, 138:1-11.
Dimiri V. P., 2000, Application of fractals in the earth sciences, A. A. Balkema, Rotterdam,157: 1405-1393.
Eslami A., And Taghaboni M., 2022, Preliminary report of 2022 earthquakes, west of Bandar Khmeir, Hormozgan province. International Institute of Earthquake Engineering and Seismology (in Persian).
Grassberger P., Procaccia I., 1983, Measuring the strangeness of strange attractors. Physica, D (9): 189-208.
Gutenberg B., Richter C.F., 1954, Seismicity of the Earth and Associated Phenomenon, second edition, Princeton University Press, Princeton.
IRSC, Iranian Seismological Center, http://irsc.ut.ac.ir
Kadinsky‐Cade K., Barazangi‏ M., 1982, Seismotectonics of southern Iran: the Oman line, Tectonics, 1 (5): 389-412, doi: 10.1029/TC001i005p00389.
Kagan Y., Jackson D., 1991, Long-term earthquake clustering. Geophys. J. Int. 104, 117–133.
Mandelbrot B., 1982, The fractal geometry of nature. W. H. Freeman & Co., San Francisco.
Mittag R.J., 2003, Fractal analysis of earthquake swarms of Vogtland/ NW- Bohemia intraplate seismicity. J.  Geodynamics, 35, 173-189.
Mogi K., 1985, Earthquake prediction. Academic Publishing, Tokyo.
Molinaro M., Guezou J.C.,  Leturmy p., Eshragh S.A., Frizon de Lamotte D., 2004, The origin of changes in structural style across the Bandar Abbas syntaxis, SE Zagros (Iran). Marine. Petr. Geol., 21:735-752.
Ommi S., and Smirnov V.B., 2024, Seismicity patterns before the 2021 Fin (Iran) doublet earthquakes using the region-time length and time-to-failure methods. Earthquake Science, 37(4): 324-336, doi: 10.1016/j.eqs.2024.04.005.
Regard V., Hatzfeld D., Molinaro M., Aubourg C.H., Bayer O., Yaminifard F., 2010, The transition between Makran subduction and the Zagros collision: recent advances in its structure and active deformation. Special Publication of Geological Society of London (330) pp.41-64.
Scholz C.H., 2002, The mechanics of earthquake and faulting, Cambridge university press.
Smalley R.F., Chatelain J.L., Turcotte D.L., Pre´ vot R., 1987, A fractal approach to the clustering of earthquakes: application to the seismicity of the New Hebrides. Bull. Seism. Soc. Am. 77, 1368–1381.
Telesca L., Nikolitanga I., Vallianatos F., 2006, Time-scaling analysis of southern Aegean seismicity: Chaos, Solitons and Fractals, v. 28, p.361–366.
Turcotte D., 1992, Fractals and chaos in geology and geophysics. Cambridge University Press.
Wiemer S., and Wyss‏ M., 2000, Completeness in earthquake catalogs: Examples from Alaska, the western United States, and Japan, Bulletin of the Seismological Society of America, 90 (4), 859-869.
Wiemer S., 2001, A software package to analyze seismicity; Zmap, Seismological Research Letter, 72(3):373-382.
Yaminifard F, Hatzfeld D., Farahbod A.M., Paul A., Mokhtari M., 2007, The diffuse transition between the Zagros continental collision and the Makran oceanic subduction (Iran): microearthquake seismicity and crustal structure. Geophysical Journal International, 170:182-194.
Yang Y.H., Li X, Hu J.C., Song J., Zhao J., Yassaghi A., Pathier E., Xu Q., Chen Q., 2023, The 2022 Hormozgan Doublet Earthquake: Two Blind Thrusts-Related Folding in Zagros Fold-And-Thrust Belt, Southeast Iran. Geophysical Research Letter, 50 (4): 1-12. Doi: 10.1029/2022GL 101902.
Zamani A., and Agh-Atabai M., 2008, Quantification of the Spatial-Temporal distribution of aftershocks associated with the 2006 Darb-e-Astaneh (Silakhor) earthquake, western Iran, Geosciences, 65: 70-79 (in Persian).