مطالعـه تغییـرات زمانـی الگـوی لرزه‌خیزی کمربند چین‌خورده-رانده زاگرس با استفاده از روش شرایدر

نوع مقاله : Articles

نویسندگان

1 گروه زمین شناسی، دانشکده علوم، دانشگاه گلستان، گرگان، ایران

2 گروه آمار، دانشکده علوم، دانشگاه گلستان، گرگان، ایران

3 پژوهشکده زلزله شناسی، پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله، تهران، ایران

چکیده

در این پژوهش برای بررسی تغییرات زمانی الگوی لرزه‌خیـزی در کمربند چین‌خورده- رانده زاگرس از الگوریتم شرایدر استفاده شد. این الگوریتم برای بررسی آرامش لرزه‌ای در مناطق مختلف به‌کار می‌رود. به همین منظور چهار زمین‌لرزه با بزرگای 6Mw≥ که اخیراً در زاگرس به وقوع پیوسته‌اند مورد مطالعه قرار گرفت. به‌منظور بررسی تغییرات زمانی لرزه-خیزی علاوه بر نمودار پیچش زمانی ((k)T)، نمودارهای بزرگی- زمان، فراوانی زمین‌لرزه‌ها- زمان و مکان-  زمان نیز ترسیم گردید. نتایج نشان می-دهد که پیش از وقوع زمین‌لرزه‌های 2006 سیلاخور و 2014 مورموری که در بخش شمال غربی زاگرس رخ‌داده‌اند، الگوی پیش‌نشانگر دونات دیده می‌شود. قبل از زمین‌لرزه‌های 2013 دشتی و 2005 قشم که هر دو در بخش جنوبی زاگرس به وقوع پیوسته‌اند، تا چندین سال آرامش لرزه‌ای مشاهده می‌شود که با وقوع ناگهانی این زمین‌لرزه‌ها خاتمه می‌یابد. نتایج تجزیه‌وتحلیل حساسیت نشان داد که پارامترهای هموارسازی الگوریتم شرایدر بر روی خروجی الگوریتم تأثیر بسزایی داشته و باید با دقت انتخاب شوند. نتایج این تحقیق نشان داد که الگوریتم شرایدر به‌دلیل استفاده هوشمندانه از پارامتر زمان (t) توانایی نمایش پیش‌نشانگر آرامش-لرزه‌ای پیش از وقوع زمین‌لرزه‌های بزرگ را دارد.

کلیدواژه‌ها


عنوان مقاله [English]

Study of the Temporal Variations of Seismicity Pattern in the Zagros Fold and Thrust Belt Using Schreider Algorithm

نویسندگان [English]

  • Maryam Sadat Mirabedini 1
  • Maryam Agh-Atabai 1
  • Majid Azimmohseni 2
  • Mostafa Allameh Zadeh 3
1 Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran
2 Department of Statistics, Faculty of Sciences, Golestan University, Gorgan, Iran
3 International Institute of Earthquake Engineering and Seismology,Tehran, Iran
چکیده [English]

Seismicity pattern studies are one of the effective tools in the interpretation of variation in seismic sequence. The study of variations of seismicity parameters as a function of time indicatesthat the temporal distribution of events is not uniform, and these parameters can give quantitative information about the seismic patterns of different regions. In this research, to investigate temporal variations of seismicity pattern in the Zagros fold and thrust belt, the Schreider algorithm is applied. This algorithm that introduced by Schreider (1990) to detect seismic quiescence has been used in different parts of the world. For this purpose, four earthquakes with Mw≥6 that have recently been occurredin Zagros have been studied. At first, a complete catalogue from the period of 2000 to 2017 within a circular area has been selected. Then, the catalogues are homogenized to ML and the Minimum magnitude of completeness are computed (Mc=3.4). To perform Schreider algorithm, the time between consecutive earthquakes (T′) should be calculated. The smoothness procedure is used to evaluate a convolution function of T′. The smoothness of this function is done by Gaussian function. In the R radius, smoothness parameter (s) has controlled the extent of surrounding earthquakes to detect smooth values. The kthseismic event is related with the temporal convolution T(k) that decrease and increase indicate seismic activity or low seismic activity, respectively. The numbers of earthquakes that are located in the nearest distance to main shock determine the l parameter. The value of l is determined when the function f(n,s) is approximately zero. Therefore, the function T(k) depends on the s and l parameters. To investigatetemporal variations of seismicity, in addition to the temporal convolution (T(k)) plot the magnitude-time, number-time and space-time plots have drawn. The results show that before the 2006 Silakhor and 2014 Mormori earthquakes, both of which occurred in the north part of Zagros, the precursory doughnut pattern is seen. Several years before the 2013 Dashti and 2005 Qeshm earthquakes, both of which occurred in the south part of Zagros, the seismic quiescence is seen for which ended with the sudden occurrence of these earthquakes. The result of sensitivity analysis showed that smoothing parameters of Schreider algorithm have a significant influence on the algorithm outcomes, and these parameters should be selected with more accuracy. The results of this papershow that Schreider algorithm can demonstrate precursory seismic quiescence before the occurrence of large earthquakes due to the intelligent usage of t parameter.

کلیدواژه‌ها [English]

  • SchreiderAlgorithm
  • Zagros Fold and Thrust Belt
  • Doughnut
  • Seismic Patterns
  • Quiescence
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