Preliminary report on South Qom earthquake of 2007 June 18, Mw 5.6 in central Iran

Description

Preliminary report on South Qom earthquake of 2007 June 18, Mw 5.6 in central Iran M. Talebian & M. Ghorashi Sesimotectonic Geoup, Geological Survey of Iran On 2007 Jun 18 an earthquake of Mw 5.6 struck a region to the South of the capital Tehran near the city Qom, The earthquake occurred at 17:59 pm local time and was felt widely by people in Qom as well as Tehran. Fortunately no damage or casualties has been reported with this moderate earthquake but the event worried people living in large cities around the epicentral area. We visited the earthquake in the day after the event. Talking to local people it seems that the strongest ground shaking has been felt in the same area as reported epicenters locate (USGS,Harv., IIEES, IRSC), however due to lack of any damage it is rather difficult to assess the intensity and make any Iso-acceleration map. All reported epicenters locate south of the surface exposure of the Qom thrust. Incised drainage and uplifted river terraces SW of the fault suggest that the Qom fault is an active thrust. This fault has been activated in the past and has caused some other earthquakes (fig. 1). We therefore suggest that reactivation of the Qom thrust with dip to the south-west is probably the source for this recent earthquake. Fig. 1: Focal mechanism and epicentral location of the south Qom earthquake. Larger spheres are two solutions for this event. Smaller ones are two earthquakes in 1980.     Fig. 2: Geological map of the region around epicenter. Long term activity along the fault has caused folding of Miocene-Oligocene deposits above the fault.   Fig. 3: Surface exposure of the Qom fault at NE limb of the anticline, south of Qom.   Fig. 4: Uplifted fan deposits on the hanging wall of the Qom thrust.