عنوان مقاله [English]
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 strike-slip and step-down faults that are fractured-crustal deformable and its evolution is influenced by processes that dominated on the strike-slip shear zones. In other words, the potential energy accumulated in this region is used as a slip along the strike-slip faults of the region, folding and non-slip creep.
Earthquake occurrence rates are an essential part of seismic-hazard 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 non-seismic 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, Dasht-e Bayaz and Tabas Faults. These faults are responsible for large earthquakes in the study area. Maximum geologic moment rate is related to West-Neh, East-Neh, Kahoorak, Abiz and Nosrat-abad 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.