شبيه‌سازي عددي رفتار اصطكاكي گسل امتدادلغز شمال تبريز با استفاده از روش المان محدود

Numerical Simulation of Frictional Behavior of Strike-Slip North Tabriz Fault Using Finite Element Method

چكيده- در اين مقاله، با استفاده از روش المان محدود، مدلي عددي از گسل امتدادلغز شمال تبريز ارايه شده است. جهت بررسي رفتار اصطكاكي گسل، مدل رفتاري ضعيف شدگي با لغزش1 به گسل اعمال مي‌شود. اين مدل بر مبناي مكانيزم ناپايداري چسب-لغز رفتار مي كند. مدلسازي گسل بر مبناي روابط المان محدود و با نرم افزارABAQUS به صورت سه‌بعدي انجام يافته كه در آن گسل به صورت صفحه اي از تماس دو ناحيه الاستيك تشكيل شده است. نتايج مدلسازي با معيارهاي زمين شناسي مانند سرعت پوسته و نرخ جابه‌جايي در صفحه گسل مقايسه گرديده كه همگرايي مناسبي بين نتايج و معيارهاي صحت سنجي مشاهده مي شود. براي اصطكاك گسل، نتايج با دو ضريب اصطكاكي مختلف با نرخ جابه‌جايي ايستگاه هاي GPSمقايسه شده كه همگرايي در ضريب اصطكاك استاتيكي 1/0 مشهودتر است.

This paper describes the three-dimensional numerical modeling of a vertical strike-slip planar fault that resides in the crust and reaches the Earthʹs surface. The goal of this study is application of a constitutive relationship which represents the governing equation of the failure process and specifies the dependence between stress, fault slip, slip rate, and other relevant physical properties. There are several laboratory-derived friction constitutive laws among which the linear slip-weakening was adopted in this paper to simulate the failure process based on stick-slip instability of faults. The finite element code (ABAQUS) is used to model the mechanical behavior of fault illustrating the distribution of stress and deformation in the Earth’s crust which involves the fault. Like other rock friction laws, slip weakening is a laboratory-derived friction law and it has three parameters which are estimated based on experimental results. In this paper the North Tabriz fault in NW of Iran is adopted for simulation. The North Tabriz Fault (NTF) is one of the active faults in NW Iran that has a clear surface expression. It has an average strike of NW-SE over a length of about 150 km and appears to be generally close to vertical in dip. Right-lateral movement along this fault, documented by Berberian and Arshadi (1976) from the study of aerial photographs, can also be seen clearly in the field. The analysis has been carried out in two steps; first the model ran for 250 years in which the fault has no friction. This step is needed to achieve the in-situ stress state in the crust. Then, the analysis continued for 100 years and in this stage the friction of fault is activated based on the slip-weakening law with these parameters : µs = 0.1 and 0.2; µd = 0.05 and Lc = 0.4 m. Another analysis has been made for time interval period in 10 years and the deformation rate of the crust was calculated in locking situation in which the fault surfaces has no relation displacement. The results of analysis show that the slip weakening law could explain the stick-slip behavior which is the main mechanism of faulting. Two stations are inside of the model geometry (KHOR & VARZ) and after the analysis was finished, the velocities of these stations are adopted for verifying the results. In the first analysis (locking phase), the results show that the convergence between GPS results and the analysis results in VARZ station is more than KHOR station. Probably, it is due to the location of these stations. Since the KHOR station is very close to the boundaries of the model and the distribution of deformation rate isn’t uniform, thus this factor can be the main source of such errors. In the second analysis, the effect of different coefficient of frictions is more sensitive in VARZ stations. The VARZ station is closer to the NTF than the KHOR station. With this treat it can be understood that the effect of variation in static coefficient of friction increases in near of the fault zone