M.A Alimi
Abstract
The sequence of seismicity including three earthquakes in the Mohammadabad region, eastern Iran, within a period of 30 years has made it one of the most outstanding seismically active regions in the country. The Mohammadabad fault system is described using earthquake and satellite imagery data to support ...
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The sequence of seismicity including three earthquakes in the Mohammadabad region, eastern Iran, within a period of 30 years has made it one of the most outstanding seismically active regions in the country. The Mohammadabad fault system is described using earthquake and satellite imagery data to support a simple tectonic model. The interaction between the Mohammadabad strike-slip fault system and basement structures and also the en-echelon array of fault segments have resulted in formation of the Mohammadabad pull-apart basin and Tajkuh contractional zone. The Daqq-e-Mohammadabad basin is a topographic depression formed in a right-step releasing step-over related to the Mohammadabad-Taleb dextral strike-slip fault system. Geomorphologic evaluation of the Mohammadabad deformation zone at surface indicates both normal and reverse faulting. Normal faulting is obvious in the margin of the basin and reverse faulting is seen in the zone of contraction at the Taleb-Tajkuh left-step restraining step-over. The model presented for the formation of adjacent extensional and contractional structures based on traces of the Mohammadabad strike-slip fault system, basin, and uplifts to the south of the area is a double step-over (releasing and restraining) model. Fault segments associated with this step-over may be capable of earthquake ruptures. The linkage of main strike-slip zones (Mohammadabad-Taleb and Taleb-Tajkuh) by transverse faults could increase potential generation of large earthquakes and activity of sympathetic faults.
M.A Alimi; M.M Khatib; KH Hessami Azar; M.R Hayhat
Abstract
An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left-stepping restraining ...
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An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left-stepping restraining stepover. Transpressional deformation in the transverse structure associated with the stepover is expressed as folding and uplifting in the Late Neogene, Quaternary and recent deposits, revealing the Shusf fault as a hidden and blind thrust. Processing of magnetic anomaly maps shows the existence of the Shusf magnetic lineament, which consistently well correlates with the Shusf fault and its hidden segments. Also the hidden part of the fault was investigated by the differential GPS profiles constructed perpendicular to the trend of the Shusf fault scarp. In this study, we used surface morphology surveys, fan median method and satellite images to calculate the cumulative horizontal and vertical offsets related to the Late Quaternary active tectonics along the Shusf fault, measuring mean values of 92 and 4.25 m, respectively. Analysis of the velocity vector recorded in the Nehbandan geodynamic station across the Shusf fault indicates the present-day evolution of the stepover expressed as uplift and left-lateral displacement.
