Document Type : Original Research Paper

Authors

1 Ph.D., Université Pierre et Marie Curie, Paris VI, Paris, France; Research Institute for Earth Sciences, Geological Survey of Iran, Teheran, Iran

2 Assistant Professor, Research Institute for Earth Sciences, Geological Survey of Iran, Teheran, Iran

3 Professor, Université Pierre et Marie Curie, Paris VI, Paris, France

4 Senior Researcher, Université Pierre et Marie Curie, Paris VI, Paris, France

5 Assistant Professor, Institute of Geophysics, University of Tehran, Teheran, Iran

6 Ph.D., Université Pierre et Marie Curie, Paris VI, Paris, France

7 Associate Professor, Islamic Azad University, North Tehran Branch; Research Institute for Earth Sciences, Geological Survey of Iran, Teheran, Iran

8 Assistant Professor, International Institute of Earthquake Engineering and Seismology (IIEES), Teheran, Iran

Abstract

The Dehshir fault system (DFS) including six fault segments forms the western border of NS-striking active dextral strike-slip fault cutting the Sanandaj-Sirjan, Uromieh-Dokhtar magmatic arc, and Central Iran. This active fault system right-laterally offset Eocene volcanic rocks and Quaternary alluvial fans. Geomorphic evidence imply the activity of the DFS in the Late Quaternary, and paleoseismic investigations revealed seismic movements along the Marvast fault segment during the Late Pleistocene and Holocene timescales. In order to unravel the seismic history of the DFS over the intermediate geologic (103 -105 yr) time scale, and based on the morphotectonics and sedimentary-stratigraphic properties, three paleoseismic sites have been selected along the 35-km-long stretch of the Marvast fault segment. The southern site (Harabarjan) shows steep fault branches of N140±10º strike with sub-horizontal striations in dextral component. Another trench has been excavated at the North Marvast site whitin the Late Pleistocene-Holocene alluvial and colluvial deposits. OSL analysis of loose quartz rich deposits yielded an age of ~72 ka for the oldest exposed sediments. Paleoseismic stduies along the Marvast fault segment provide evidence for the occurrence of several large seismic events associated with surface ruptures along the DFS. The chronology of paleoearthquakes on the Marvast segment indicates that at least 7 large (≈Mw > 7) earthquakes occurred in the last 43 ka with an average recurrence time of 3650±150 years. The most recent earthquake, event I, occurred ~2200 years ago, which associated with 2-4 m of dextral slip and >40 km surface rupture along the Marvast fault segment. These investigations are compatible with the lack of destruction in the Marvast historical (~1300 years) castle, located

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