Document Type : Original Research Paper


1 Research Institute for Earth Sciences, Geological Survey of Iran, Teheran, Iran

2 Université Pierre et Marie Curie, Paris VI, Paris, France

3 The Institute of Geophysics, University of Tehran, Teheran, Iran

4 International Institute of Earthquake Engineering and Seismology (IIEES), Teheran, Iran


The evaluation of  seismic potential along the Dehshir fault with 550-km  length (by count of northern and southern splays) is critical considering that more than 3.5 million people live in cities and towns located at vicinity of the fault. The Dehshir fault is considered as westernmost limit of N-striking dextral strike-slip faults set that slice Central and eastern Iran. Due to the  lack of large recorded earthquakes (instrumental and historical) in Central Iran, access to seismic potential of active faults by studying the earthquake catalogs seems to be impossible. No instrumental earthquake has been recorded greater than mb 4.7 around the Dehshir fault and also historical data shows no evidence for occurrence of large earthquake around the fault. No sign of destruction in Marvast historical castle (at a less than 10 km far from the Dehshir fault) built in Islamic period (~700-1250), shows any remarkable seismic activity until 750-1300 years ago. However, several evidence of geomorphologic markers such as drainages, gullies, streams and alluvial fans offsets, represent activity of the Dehshir fault in Late Quaternary. Of Geomorphic evidence at Marvast and Harabarjan sites record dextral - slip on the Dehshir fault during the Late Pleistocene-Holocene as major movement with minor dip - slip component. Rake of the fault movement has been considered for assessing to amount of horizontal and vertical slip rate on the Dehshir fault. This value in the North Marvast site has been calculated ~10 degrees and according to right bank offset on the Marvast river is ~7 degrees with horizontal and vertical displacements of 13 m and 1.5 m, respectively. Combining cumulative offset markers with OSL dating implies the Dehshir fault in Late Pleistocene-Holocene time period slips at horizontal and vertical components about 1±0.3 and 0.1 mm yr-1, respectively. We observed a minimum dextral offset along the Marvast fault segment in west of Harabarjan about 2 m that allow us assuming the related magnitude and date of last large paleoearthquake on the Dehshir fault is about Mw 7 and 2000 years ago, respectively.  


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