ارزیابی توان لرزه‌خیزی پهنه لوت با مقایسه نرخ گشتاورهای ژئودتیک، لرزه‌ای و زمین‌شناسی

نرخ گشتاور بیانگر میزان انرژی است که در سامانه‌های دگرریختی صرف می‌شود و به سه روش ژئودتیکی، لرزه شناسی و زمین‌شناسی به دست می آید. در این پژوهش پهنه‌ی لوت به پنج ناحیه ساختاری تقسیم شده است. بیشترین مقدار نرخ گشتاور به‌دست‌آمده مربوط به گشتاور ژئودتیک می‌باشد که برابر با nm/yr 10^19×1.2118 می‌باشد. نرخ گشتاور لرزه‌ای nm/yr 10^18×3.9456 و در نهایت نرخ گشتاور زمین‌شناسی نیز معادل  nm/yr10^16×2.4882 محاسبه شد. مقایسه نرخ گشتاور ژئودتیک و لرزه‌ای نشان می‌دهد دگرشکلی بین لرزه‌ای در پهنه لوت 3.07 برابر دگرشکلی لرزه‌ای در این منطقه می‌باشد. نسبت نرخ گشتاور لرزه‌ای به ژئودتیک در ناحیه‌های 1 تا 5 به‌ترتیب برابر با 0.69، 0.55، 2.36، 0.03 و 0.02 برآورد شده است که نشان می‌دهد واتنش در بخش‌های شمالی سریع و در بخش‌های جنوبی کند می‌باشد. نسبت نرخ گشتاور زمین‌شناسی به لرزه‌ای نشان می‌دهد 0.63 درصد از کل انرژی پتانسیل موجود در گسل‌ها به‌صورت زمین‌لرزه در طی کاتالوگ زمین‌لرزه‌ای آزاد شده است و بخش زیادی از انرژی همچنان باقی است و می‌تواند در آینده آزاد شود. با بررسی نرخ‌های گشتاور ژئودتیک، لرزه‌ای و زمین‌شناسی در ناحیه‌های مختلف پهنه لوت، به نظر می‌رسد خطرناک‌ترین بخش پهنه لوت از لحاظ پتانسیل لرزه‌خیزی ناحیه جنوب خاور لوت باشد که منطبق بر سیستم گسل نهبندان از جنوب گسل آبیز تا مرزهای جنوبی پهنه‌ی لوت می‌باشد.

Estimation of the Seismicity Potential, Based on Geodetic, Seismic and Geological Moment Rate in the Lut Block

The Lut Zone, with about 900 km length, is in the eastern part of central Iran. The eastern boundary of this zone is specified by the Nehbandan fault and the eastern Flysch of Iran and its western border by the Nayband fault and the Tabas block. East of Iran consists of a series of strikeslip and stepdown faults that are fracturedcrustal deformable and its evolution is influenced by processes that dominated on the strikeslip shear zones. In other words, the potential energy accumulated in this region is used as a slip along the strikeslip faults of the region, folding and nonslip creep.Earthquake occurrence rates are an essential part of seismichazard analysis. Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. There are now three major types of data available to estimate these occurrence rates: Geodetic moment rate, seismic moment rate (on the basis of historical and instrumental earthquake data) and geologic moment rate are estimated for Lut block in east of Iran. Lut block was affected by several large earthquakes in the past causing heavy damage in this region. Each approach has limitations, but in principle they should all yield similar estimates.Firstly, a catalog of historical and instrumental earthquakes was used. Then, while preparing the fault maps of the region, regarding the geometric information of the active faults, the latest information on the geometrical characteristics of the faults has been collected. Finally, geological, seismic and geodetic moment rates for the region were estimated and the results were compared. Depending on the type of deformation and geometry of fault, the study area divided to the five zones: northwestern (zone 1), southwestern (zone 2), north and northeastern (zone 3), southwestern (zone 4) and southern zone (zone 5). Then we compare the value of three types of moment rate in these zones to each other. The most moment rate in the Lut block belongs to geodetic approach (1.2119x1018 Nm/yr) and then seismic moment rate (3.9455x1018 Nm/yr), and finally the least quantity belongs to geologic moment rate (2.4882x1016 Nm/yr).Each of these calculating methods of moment bring from a different perspective that can show different patterns in the style and extent of tectonic activity in the region. Geodetic moment rates include both seismic and nonseismic deformations and cover a highly short time range. Therefore, it is obvious that it shows higher values than the other two methods. The most of seismic moment rate was obtained respectively in Zone 3, 1, 4, 5 and 2. According to seismic map, maximum seismic moment is along Abiz, Dashte Bayaz and Tabas Faults. These faults are responsible for large earthquakes in the study area. Maximum geologic moment rate is related to WestNeh, EastNeh, Kahoorak, Abiz and Nosratabad Faults. According to values of geological and geodetic moment rates in the southeastern of Lut area and based on the value of the release seismic energy in the north and western part of Lut area, it seems that in the next time, the most of seismic potential and seismic hazard are in the southeastern part of the study area.According to the ratio of seismic to geodetic moment rate can be concluded that the northern part and northwestern part with ratio 2.36 and 0.69 are fast strain areas and south, southwestern and southeastern part with ratio: 0.055, 0.02 and 0.03 are fast strain areas, respectively. Ratio of the geodetic moment rate to the seismic moment rate obtained more than 3.07, which reflects the important role of the interseismic deformation in this area. Ratio of seismic moment rate to geological moment rate is 0.63 %. This value indicates that 0.63 % potential of the faults for seismic energy has been released ant not been released a significant part of the elastic energy in the area.