مدل‌سازی عددی گسل جبهه کوهستان (MFF) در رخداد زلزله‌ 21 آبان 1396 سرپل‌ذهاب به‌روش عنصر مرزی

نوع مقاله : مقاله پژوهشی‌

نویسندگان

1 دانشجوی دکتری مهندسی ژئوتکنیک، گروه مهندسی عمران دانشگاه رازی، کرمانشاه، ایران

2 استادیار، گروه مهندسی عمران دانشگاه رازی، کرمانشاه، ایران

3 استاد، گروه مهندسی ژئوتکنیک لرزه‌ای، پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله، تهران، ایران

چکیده

در اثر زلزله 21 آبان 1396 سرپل­ذهاب با بزرگای 3/7=Mw تغییرمکان­های سطحی به‌ویژه زمین­لغزش بسیار بزرگ مله­کبود و پس­لرزه­های زیادی به‌صورت خوشه­های پراکنده در منطقه رخ داد. وقوع پس­لرزه­ها به‌صورت خوشه­ای نشانی از فعالیت گسل­های کوچک از قبل موجود می­باشد. در مطالعه حاضر گسل مسبب زلزله اصلی (گسل جبهه کوهستان (MFF)) با استفاده از کد عنصر مرزی سه‌‌بعدی 3d-def مدل‌سازی شد و میزان تغییر مکان­های­ سطحی به‌ویژه جابه‌جایی حاصل از زمین‌لغزش مله­کبود و همچنین محل گسل­های ثانویه با استفاده از میانگین تنشهای اصلی بیشینه و کمینه به‌عنوان معیاری برای تعیین محل گسل­های ثانویه استخراج گردید. به‌منظور صحت‌‌سنجی نتایج مدل‌سازی برای جابه‌جایی­ها، از مقایسه نتایج با داده­های به‌دست‌آمده از روش تداخل‌‌سنجی راداری (InSAR) و روش ترکیبی ردیابی افست (combined offset tracking) مشاهده شد که نتایج دو روش تقریباً به همدیگر نزدیک می­باشند و اختلافاتی نیز در موقعیت جابه‌جایی­ها و دامنه تغییرات آنها در دو روش دیده می­شود به گونه­ای که دامنه تغییرات جابه‌جایی حاصل از داده­های ماهواره­ای در منطقه زلزله، 35- تا 80 سانتی‌متر است در حالی‌که این محدوده برای نتایج حاصل از مدل‌سازی انجام شده، 15- تا 100 سانتی‌متر می­باشد. همچنین برای محل گسل­های ثانویه، میانگین تنشهای اصلی بیشینه و کمینه حاصل از مدل‌سازی تقریباً در محل­های دارای تراکم پس­لرزه­ به‌ویژه در قسمت جنوبی گسل بیشینه می­باشد و عمق­های با بیشترین میانگین تنشهای اصلی بیشینه و کمینه  با عمق‌هایی که تراکم پس­لرزه زیاد است، به‌جز در عمق 13کیلومتری به پایین تقریباً یکی می­باشند. علاوه‌بر این برای تعیین میزان حساسیت مدل نسبت به پارامترهای ورودی تحلیل حساسیت انجام شد که در نتیجه آن تغییرات پارامترهای شیب و عرض گسل، بیشترین اثر را بر خروجی جابه‌جایی و همچنین تغییرات پارامترهای مدول یانگ و طول گسل بیشترین اثر را بر خروجی میانگین تنشهای اصلی بیشینه و کمینه داشتند.              

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical modeling of mountain front fault (MFF) in the event of earthquake on November 12, 2017 Sarpol-e-Zahab by boundary element method

نویسندگان [English]

  • Sayed Yadegar Hoshyar 1
  • Iman Ashayeri 2
  • Mohsen Kamalian 3
1 Ph.D. student in Geotechnical Engineering, Department of Civil Engineering, Razi University, Kermanshah, Iran
2 Assistant Professor, Department of Civil Engineering, Razi University, Kermanshah, Iran
3 Professor, Department of Seismic Geotechnical Engineering, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
چکیده [English]

The earthquake of November 12, 2017 Mw=7.3 Sarpol-e-Zahab is located in western Iran and between the two faults of the Mountain Front (MFF) and the High Zagros (HZF) of the Zagros tectonic seismic zone, Which is related to the rupture of MFF fault in Sarpol-e-Zahab area.The focal mechanism of this earthquake has a reverse fault with a low slope (16 degree) to the northeast. Studies in this field indicate the existence of a maximum slip of about 5 meters at a depth of 18 km. Due to the earthquake on November 12, 2017, Mw=7.3 Sarpol-e-Zahab, surface displacements, especially very large landslide of Mela-Kabod and many aftershocks occurred in the form of scattered clusters in the region. The occurrence of aftershocks in clusters indicates the activity of small secondary faults. In the present study, the fault causing the main earthquake (Mountain Front Fault, (MFF)) was modeled using 3d-def three-dimensional boundary element code and the surface displacements, especially displacement due to the landslide of Mela-Kabod and also the location of secondary faults were extracted using average of maximum and minimum principal stresses as a criterion for determining the location of secondary faults. In order to validate the modeling results for the displacements, comparing the results with the data obtained from the Interferometric Synthetic Aperture Radar (InSAR) method and the combined offset tracking method, it was observed that The results of the two methods are almost close to each other and there are differences in the position of the displacements and the amplitude of their changes in the two methods, so that the amplitude of the displacements resulting from satellite data in the earthquake zone, It is -35 to 80 cm, while this range is -15 to 100 cm for the results of the modeling. Also, for the location of secondary faults, the  average of maximum and minimum principal Stresses resulting from modeling are almost maximal in areas with aftershock density, especially in the southern part of the fault, and the depths with the most average of maximum and minimum principal stresses with depths that The aftershocks are high, except at a depth of 13 km, those are almost the same. In addition, to determine the sensitivity of the model to the input parameters, sensitivity analysis was performed, As a result, changes in dip angle and width of fault had the greatest effect on displacement output and also changes in Young modulus and length of fault had the greatest effect on  average of maximum and minimum principal stresses output. The boundary element method used in this paper is one of the numerical modeling methods that has many applications in numerical simulation of fault dynamics, and its results have provided a broad view of the physics of earthquake rupture. Also, the compatibility of numerical modeling results with the results of radar interferometry (InSAR) and combined offset tracking in this paper shows that the boundary element method is a suitable method for numerical modeling of faults.

کلیدواژه‌ها [English]

  • Sarpol-e-Zahab earthquake
  • Mela-Kabod landslide
  • aftershocks
  • MFF fault
  • secondary faults
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