Category Other
Group GSI.IR
Location 8th international seminar earthquake prognostics
Holding Date 03 March 2008

     Iran is situated in a highly seismic part of the Alpine-Himalayan belt, and has been frequently struck by catastrophic earthquake during recorded history. Seismotectonically, Iran can be divided into four broad seismotectonic provinces (Berberian 1981): 1) The Zagros active fold-thrust belt, 2)The Makran accretionary flysch belt, 3)The Central Iranian plateau, and 4) the Alborz Mountains. In the Zagros belt the metamorphosed Precambrian basement is covered by 10 to 12 kilometers of sedimentary rocks which fold during late Miocene - Pleistocene time. A highly plastic salt layer of late Precambrian (Hormoz Salt) and several other plastic layers
within the sedimentary cover, act as "Zone of slippage" disconnecting the sedimentary cover structures from those in the basement, and usually no earthquake rupture is observed at the surface. The Makran region is an unusually wide deformed accretionary sediment prisms formed from material scrapped off the northerly subducting oceanic lithorphere of the Gulf of Oman underneath the Central Iranian continental margin. The zone is characterized by a low and scattered seismicity compared with the Zagros active fold thrust belt. lack of seismicity along the subduction zone could be due to the very shallow angle of subductions. Seism ically, Central Iran is characterized by "sporadic and discontinuous" earthquake activity with large magnitude shallow earthquakes along mountain-bordering reverse faults which have been formed and reactivated during previous orogenic phases. large magnitude earthquakes in Central Iran are usually characterized by long recurrence periods along frontal reverse faults and the recent aseismic period along some major recent Iranian faults presumably gradually by large magnitude earthquakes. Although reverse faulting and folding plays an important role in building the Alborz mountain  belt, the 20.6.1990 Rudbar - Tarom event showed that the mountain belt in the epicentral regions underwent significant left-lateral shear (Berberian et al. 1992).

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