مجله ژئوفیزیک ایران

مجله ژئوفیزیک ایران

بررسی رفتار دینامیکی گسل شمال تبریز در دوره بین لرزه‌ای با استفاده از مدل‌های فیزیکی چرخه زمین لرزه در نیم‌فضای گرانروی کشسان

نوع مقاله : مقاله پژوهشی‌

نویسندگان
1 کارشناسی ارشد، دانشکده مهندسی نقشه برداری، دانشگاه خواجه نصیرالدین طوسی، تهران، ایران
2 استادیار، گروه مهندسی نقشه‌برداری، دانشکده مهندسی عمران، دانشگاه تبریز، تبریز، ایران
3 استاد، دانشکده مهندسی نقشه‌برداری، دانشگاه خواجه نصیرالدین طوسی، تهران، ایران
چکیده
پیشرفت‌های قابل‌توجهی در درک مکانیسم‌ها و مکان‌های دخیل در تجمع کرنش بین‌لرزه‌ای در امتداد گسل‌ها حاصل شده است که شناسایی بخش‌های گسلی با تمایل بالاتر برای وقوع زلزله را تسهیل می‌کند. با این وجود، پاسخ مکانیکی در انتقال از قفل شدگی گسل به رفتار خزشی گسل مبهم باقی می‌ماند. برآورد دقیق کسری لغزش در چنین مناطق انتقالی یک چالش پیچیده است. فرض رایج در وارون‌سازی‌های ژئودتیکی برای نرخ‌های تغییر شکل سطحی در نظر گرفتن توزیع عمق نرخ لغزش بین لرزه‌ای در امتداد گسل به صورت ثابت در طول زمان است. مدل اولیه مورد استفاده برای محاسبه تغییر شکل گسل، مدل تانژانت معکوس است که با پیشرفت‌های بعدی که منجر به توسعه مدل‌هایی مانند مدل Okada شد. محدودیت اولیه این مدل‌ها از فرض عمق قفل‌شدگی ثابت آنها ناشی می‌شود که منجر به مشکلات تکینگی در خلال حل قضیه تنش می‌شود و معادلات خاصی را بی‌پاسخ می‌کند. در این مطالعه، فرض عمق قفل‌شدگی ثابت رد می‌شود و مشکل تکینگی با در نظر گرفتن عمق قفل متغیر حل می‌شود. روش بکار گرفته شده در این تحقیق بر انتشار خزش در محیط کشسان متمرکز است و این امر مستلزم محاسبه تغییر شکل طولانی مدت ناشی از جریان ویسکوالاستیک در گوشته بالایی و پوسته پایینی است. در حالی که مدل‌های کاملاً الاستیک معمولاً اعماق قفل‌شدگی را بیشتر از اعماق لرزه‌ای برآورد می‌کنند، گنجاندن اثرات ویسکوالاستیک باعث بهبود تناسب با نرخ‌های تغییر شکل بین‌لرزه‌ای می‌شود. در این تحقیق، میدان سرعت با استفاده از روش مسئله مستقیم و المان مرزی بازیابی می‌شود و متعاقباً از یک رویکرد وارون سازی مبتنی بر فیزیک (خزش عمیق بین لرزه‌ای) برای استنباط مقادیر پارامترهای عمق گسیختگی کامل، ضخامت الاستیک، نرخ لغزش، جابجایی همالرزه‌ای، زمان آرامش لرزه‌ای، دوره بازگشت لرزه‌ای، عمق قفل شدگی، عمق خزش یکنواخت و سرعت انتشار در گسل شمال تبریز استفاده می‌شود.
کلیدواژه‌ها

عنوان مقاله English

Investigating the dynamic behavior of the north Tabriz fault in the interseismic period using physical models of the earthquake cycle in a viscoelastic half-space

نویسندگان English

Milad Salmanian 1
Asghar Rastbood 2
Masoud Mashhadi Hossainali 3
1 M.Sc., Faculty of Geodesy and Geomatics Engineering, K. N. Toosi University of Technology, Tehran, Iran
2 Assistant Professor, Department of Geomatics Engineering, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran
3 Professor, Faculty of Geodesy and Geomatics Engineering, K. N. Toosi University of Technology, Tehran, Iran
چکیده English

Significant progress has been made in understanding the mechanisms and locations involved in the accumulation of interseismic strain along faults, which facilitates the identification of fault segments with higher earthquake propensity. Nevertheless, the mechanical response during the transition from deep fault locking to creep behavior remains obscure. Accurate estimation of the slip fraction in such transition zones is a particularly complex challenge. A common assumption in geodetic inversions for surface deformation rates involves treating the depth distribution of interseismic slip rates along the fault as constant over time. The primary model used to calculate fault shape changes is the inverse tangent model introduced in 1973, with subsequent developments leading to the development of models such as the Okada model. The primary limitation of these models comes from the assumption of their constant locking depth, which leads to singularity problems during the solution of the stress theorem and leaves certain equations unanswered. In this study, the assumption of constant locking depth is rejected and the singularity problem is solved by considering variable locking depth. The method used in this research is focused on creep propagation in a perfectly elastic medium. This requires accounting for long-term deformation caused by viscoelastic flow in the upper mantle and lower crust. While fully elastic models typically produce locking depths greater than seismic depths, the inclusion of viscoelastic effects improves the fit to interseismic deformation rates, particularly showing lower locking depths. In this research, the GPS velocity field is recovered using the forward problem and boundary element method and subsequently from a physics-based inversion approach (deep interseismic creep) to infer the values of the parameters full rupture depth (D) and elastic thickness (H), slip rate , coseismic displacement (c), relaxation time , recurrence time (T), locking depth (d), uniform creep depth , and propagation velocity  in the North Tabriz Fault is used. By overcoming the inherent limitations of traditional models, this study provides valuable insights into the complexities of fault dynamics and interseismic slip behavior. The proposed approach not only enhances the accuracy of slip models but also improves the understanding of fault mechanics in transition zones. The findings suggest that variable locking depths may contribute significantly to the characterization of fault behavior, offering a refined perspective on the seismic risk assessment of fault systems. This work thereby underscores the necessity of integrating viscoelastic considerations in future geophysical models to better predict fault response under varying stress regimes.

کلیدواژه‌ها English

Interseismic creep
boundary element method
markov chain monte carlo
GPS velocity field
earthquake cycle
North Tabriz Fault (NTF)
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