Abstract
The Astaneh Fault is classically described as the source of the mostdestructive seismic event in the history in Northeastern Iran, the 856 CEQumis earthquake with an estimated magnitude between 7.4 and 7.9. In thisarticle, based on the results obtained from paleoseismological researchesfrom trenches AT1, AT2, AT3, AT4 and AT5 along the Astaneh Fault, wewill determine the magnitude of past earthquakes and their aftershocks. Thepaleoseismological study along the fault in the two argillic sagpond of Playaand Graben structures provides evidence of 5 to 8 earthquakes in the past,which were determined by using the luminescence and radiocarbon agedating. The youngest seismic rupture was observed in the AT5 trench in theperiod of 700 ± 20 years BP and 1370 ± 140 years IRSL age, which can beconsistent with the historical rupture of the Qumes earthquake. Analysis andmeasurement of morphological analysis along the fault zone estimates theequivalent displacement of 3.9±0.3 meters for the penultimate earthquake.The surface rupture indicates a moment magnitude between 7.3 and 7.5,comparable to the magnitude estimated for the historical 856 Qumis event.The distribution of past events over time shows a quasi-periodic seismicpattern with a mean return period of 1800 ± 230 years