RECENT FAULTS OF THE ZAGROS FOLD BELT

The Zagros region of southwest Iran is generally considered a tectonically active region that lacks any surface expression of recent faulting. Of the earthquake fault scarps that have been identified, only a few have been attributed to events that occurred in the last Century.

Detail photogeology and field observations of the area, especially the Fars province, show that, there are tens of recently activated faults .All of these are high angle reverse faults located within synclines, parallel to the fold axis and dipping towards the synclinal cores. The faults are located at the lower contacts of competent layers inter-bedded with marls of Tertiary formations. Clear displacements of the recent fan deposits and over thrusting of Tertiary formations above the recent alluvial fans indicates recent activity. The faults range from 2- 30 kilometers in length and have up to 15 meters of vertical displacement. Displacement decreases with depth going to zero within Tertiary formations. Obvious exposures of these faults are located at the north and northwest of Bandar-Abbas, north of Bandar-Lengeh, northeast of Busher and east of Kazeroun cities.

Structural analysis of the fault affected synclines and surrounding anticlines shows that the core of the synclines are pinched out to accommodate a room problem related to NE-SW shortening of the sedimentary sequence.

Synclinal tightening and fold core uplift is due to a decrease in wavelength and an increase in amplitude as shortening progresses. This progress also requires simultaneous slip on the major north dipping, curved, blind thrust faults which sole into a detachment horizon and tip-out in the cores of the main anticlines. The observed surface faulting therefore implies that many of the blind thrusts of the region have been activated during the last few centuries.