سعید زارعی

Iranian Plateau has been frequently struck by catastrophic earthquakes resulting in the massive loss of life, large masses homeless and disrupting their agricultural and industrial lifelines. Southeast of Iran experienced 8 earthquakes during 30 years from 1981 to 2011. Northwest of Iran experienced historical and instrumental large earthquakes too. On 11 August 2012, a strong earthquake with magnitude Mw 6.4 occurred in Ahar- Varzaghan region, NW of Iran. It followed by another strong earthquake with magnitude Mw 6.2 after 11 minutes. The influence of static stress transfer due to moderate-to-large earthquakes on the occurrence of future earthquakes had been proved by numerous studies. This effect in triggering future events and spatial distribution of aftershocks can be explained by using the Coulomb stress changes theory. We calculated the static Coulomb stress changes for the southeast of Iran due to earthquake sequence from 1981 and for the northwest of Iran due to Ahar-Varzaghan earthquakes. In the southeast of Iran, our calculations showed a positive stress changes due to previous events on the rupture plane of next earthquake and only plane of the Rigan earthquake of 2010 December 20 received negative stress changes. Also, we calculated imparted stress changes on the surrounding active faults and showed that hypocenter of recent Hojedk earthquakes (2017 December 1 and 12) with a moment magnitude of 6.1, 6.2, and 6.1 respectively, received positive stress changes. The imparted stress by the twin Ahar- Varzaghan earthquakes on North Tabriz Fault (NTF) system showed an increase on the eastern part of the NTF near the Bostanabad about 30 km southeast of Tabriz city and northwest part of this fault system. Furthermore our calculation showed positive Coulomb stress changes on the North and South Bozgush faults.