مجله ژئوفیزیک ایران

مجله ژئوفیزیک ایران

ماهیت فرکتالی الگوی لرزه‌خیزی پیش از زمین‌لرزه‌های دوگانه 1401 هرمزگان، جنوب ایران

نوع مقاله : مقاله پژوهشی‌

نویسندگان
1 دانشیار، گروه زمین‌شناسی، دانشکده علوم، دانشگاه گلستان، گرگان، ایران
2 دانشجوی کارشناسی ارشد تکتونیک، گروه زمین‌شناسی، دانشکده علوم، دانشگاه گلستان، گرگان، ایران
چکیده
دو زمین­لرزه با بزرگای گشتاوری (Mw) بیش از 6 در تاریخ 11 تیر 1401  هجری­شمسی در غرب بندر خمیر استان هرمزگان در جنوب ایران رخ‌دادند. کانون سطحی این زمین­لرزه­ها بر روی یک زون متراکم لرزه­خیزی، با روند شمال­شرق-جنوب غرب انتهای جنوب شرقی کمربند چین­خورده رانده زاگرس در جنوب ایران قرار دارند. در این پژوهش، تغییرات زمانی پارامترهای فرکتالی لرزه­خیزی شامل b-value و ابعاد فرکتالی مراکز سطحی و زمان رویداد زمین­لرزه­ها پیش از این زمین­لرزه­ها بررسی شد. داده­ها در محدوده­ دایره­ای شکل به مرکزیت کانون سطحی زمین­لرزه اول و شعاع 60 کیلومتر برای یک دوره زمانی 5/3 ساله (از ابتدای 2019 تا زمان رویداد زمین­لرزه­ها) از مرکز­ لرزه­نگاری ایران برگرفته شد. بر اساس نتایج این پژوهش، تا قبل از سال 2021 (5/1 سال پیش از رویداد زمین­لرزه­های هدف) پارامترهای فرکتالی تغییراتی متناسب با رخداد خوشه­های لرزه­ای متعدد این دوره زمانی نشان می­دهند. بین سالهای 2021 و 2022 روند تغییرات دو پارامتر b-value  و Dt پس از یک افزایش قابل توجه و De نسبتاً پایدار بوده است. سپس هر سه پارامتر لرزه­خیزی در یک دوره زمانی چند ماهه پیش از زمین­لرزه­های اصلی الگوی مشابه (افزایش مقدار) نشان داده­اند. بررسی نمودارهای نرخ ماهانه لرزه­خیزی و بزرگا-زمان نشان داد که نرخ لرزه­خیزی از اوایل سال 2021 تا قبل از زمان رویداد زمین­لرزه­های اصلی غرب بندر خمیر بسیار کم و زمین­لرزه­ها بصورت پراکنده در زمان رخ داده­اند. اما نمودارمکان-زمان نشان می­دهد که چند ماه قبل از وقوع زمین­لرزه­های اصلی یک دوره­ ­آرامش ­لرزه­ای در اطراف زمین­لرزه اصلی حاکم بوده و هم­زمان با آن در شمال منطقه لرزه­خیزی تداوم داشته است. نظر می­رسد تغییرات معنادار پارامترهای فرکتالی لرزه­خیزی در زمان حدود چند ماه پیش از رویداد زمین­لرزه اصلی به دلیل آرامش لرزه­ای حاکم بر منطقه است که می­توان آن­ها را به عنوان پیش­نشانگر میان­مدت زمین­لرزه­های 2022 غرب بندر خمیر استان هرمزگان معرفی کرد.
 
کلیدواژه‌ها

موضوعات


عنوان مقاله English

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

نویسندگان English

Maryam Agh-Atabai 1
Fatemeh Manchar 2
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
چکیده English

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.

کلیدواژه‌ها English

Precursor
seismicity pattern
clustering
transition zone
Zagros
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