Document Type : Research Paper

Authors

1 UNESCO Chair on Coastal Geo-Hazard Analysis, Research Institute for Earth Sciences, Tehran-Iran

2 Laboratoire Géosciences Montpellier - UMR 5243, Université de Montpellier, France

3 Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement, CEREGE-France

4 Geological Survey of Iran, Tehran-Iran

5 US Geological Survey, Box 25046, M.S. 974, Denver CO 80225, USA

6 UMR IDES, Université Paris-Sud, 91405 Orsay, France

7 UMR IDES, Université Paris-Sud, 91405 Orsay, France

8 : Faculty of Geology, University of Tehran, Tehran-Iran

Abstract

Abstract

The Astaneh Fault is classically described as the source of the most destructive seismic event in the history in North-Eastern Iran, the 856 Qumis earthquake with an estimated magnitude between 7.4 and 7.9. In this article, based on the results obtained from paleoseismological researches from trenches AT1, AT2, AT3, AT4 and AT5 along the Astaneh Fault, we will determine the magnitude of past earthquakes and their return period. The paleoseismological study along the fault in the two argillic sagpond of Playa and Graben structures provides evidence of 5 to 8 earthquakes in the past, which were determined by using the luminescence and radiocarbon age dating.

The youngest seismic rupture was observed in the AT5 trench in the period of 700 ± 20 years BP and 1370 ± 140 years IRSL age, which can be consistent with the historical rupture of the Qumes earthquake. Analysis and measurement of morphological analysis along the fault zone estimates the equivalent 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 seismic pattern with a mean return period of 1800 ± 230 years.

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