Assessing seismic hazards of blind thrusts by surface deformation: Kheyrabad anticline, Eastern Iran

In this research, we investigate the seismic hazard associated with the Kheyrabad blind thrust fault at the north of Birjand, Eastern Iran. Field measurements from a structural transect through the Kheyrabad anticline indicate fault-propagation folding above a 38° northeastward-dipping blind thrust fault which probably reaches into a horizontal detachment at a depth of ~500 meters. In this research, in order to evaluate the seismic risk of Khayrabad blind fault have been investigated, parameters such as average slip rate, maximum earthquake (Mmax) and its recurrence. Obtaining estimates of the slip-rate on the blind fault, and of the rate of crustal shortening are difficult, but we assume that transport of material on the horizontal decollement at depth is balanced by extrusion of material at the surface, we can produce approximate measurements of slip-rate and shortening by using area balancing. In this method, the rates of fault slip, horizontal shortening, and uplift have been estimated as 0.75, 0.59, and 0.46 mm/yr, respectively. Using the regression equation between earthquake magnitude and rupture area, magnitude of the maximum earthquake is estimated at 4.7. Also, using the empirical relationships between magnitude, coseismic displacement and slip rate, the recurrence of this earthquake is predicted to be 577 years. According to the obtained slip rate (0.75 mm/yr), the activity grade of Khairabad blind fault is considered moderate.