PANAF 2012 New Paleoseismology studies in -Silvana region

Ciabeghodsi,A.(1), Nikrouz, R. (1)

(1) Urmia University, Department of , Urmia, Corresponding Author: Ciabeghodsi, A. ([email protected] [email protected])

In this study we review the limited history of paleoseismological investigation in (North West of Iran) and discuss the potential contribution of active fault source data towards improving our understanding of seismicity. The availability and suitability of Urmia- Silvana active fault source data for incorporation into future probabilistic hazard model is assessed, and appropriate methodologies for achieving this proposed. Azerbaijan is the site of convergent plate collisions along the Alpine-Himalayan active mountain belt. Brittle faults in the Azerbaijan area are mostly composed in Cenozoic geological time or younger of this time. The data presented demonstrate clearly that geological structures are commonly repeated at all scales from outcrop to regional area. In order to forecast earthquake activity we need to determine the past history of faults. One of the active fault in the study area is likely to move again toward north diriction. This region is a part of ophiolite and changing belt of Sanandaj-Sirjan zone according to division of sedimentary-constructive units of Iran . This region which is a part of is the western part of geological state of Iran that has been covered with younger sediments and considerable width that Silvana`s complex sediments have been put on them. In next areas faults that have tremble potential are evaluated. Among this area there are Urmia fault , Drik fault , Silvana`s fault ,Oshnavieh fault and other active faults. In regard of fault's activities ,special structural micro zones in the region established , as Salmas zone , Western zone of Urmia lake , zone and southern islands of Urmia lake have varity of tectonic qualities shows fault's situation in the study area. To show the Urmia-Silvana`s fault, four trenches have excavated at two different sites to study the past earthquake history to resolve slip and constrain the earthquake history on a channel–fan complex that crosses the fault at a high angle. A distinctive, well-sorted fine sand channel that served as a marker unit was exposed in four trenches totaling over 150 m in length. Isopach mapping shows that the sand is channelized toward north of the fault and shows overflow fan complex across a broad fault scarp to the west. The study ofpalaeoseismic observations suggest that the Urmia – Silvana`s fault of the Azerbaijan ruptures every one and half centuriesconsistent with the historical record for the region.

Key word: Paleoseismology, Brittle faults, Active fault, Microzone

8-10 October 2012 Istanbul Technical University – Turkey www.panaf.itu.edu.tr