Shonbeh Earthquake of 09 April 2013, Mw=6.4
On 9 April 2013 at 11:52 UTC (16:22 local time), a Mw 6.4 earthquake occurred at the depth of 20 Km in Dashti district in south-west Iran’s Bushehr province. The macroseismic epicenter was located near the city of Shonbeh. The earthquake caused 37 deaths and 850 injuries. Over 1,000 houses in 92 villages were damaged. Since the earthquake happened in the afternoon, most of the people were outdoors, so about 60% of the victims were either women or elderly family members. The event destroyed 100 houses, left 1000 homeless, and damaged 500 more houses in nearby villages. The early financial assessment of the earthquake losses by the governor general of Bushehr Province was about $50 million USD (Mehr News Agency, April 10, 2013). According to the Euro-Mediterranean Seismological Center (EMSC), the earthquake exhibited an almost pure thrust focal mechanism, with a NW–SE fault plane and a focal depth of 10 km. Other reports on focal mechanisms (i.e., by the USGS) show a mostly compressional strike-slip component. The most important fault in the epicentral region is the Borazjan fault, having a north-south strike with a NNW-SSE trend. The fault segment is known to be about 100km long, and it is located in the east of the Mond anticline. The fault passes from the western part of the Jashk Salt Diapir, one of the largest and most active salt domes of Iran, about 144 km southeast of Bushehr. The dome is 1350 m above sea level. Some NNW-SSE surface fissures (N300-320) were observed in the foothills of this mountain after the earthquake. Near Shonbeh (4km southeast of the city) there was clear evidence of liquefaction along the Mond River in the Dashte-Zaal (“white plain”). Some surface tension cracks were induced by liquefaction in the Mond River terrace. These features could be seen along about 3 km of the terrace. Surface fissures along the reported causative fault could be observed south of Shonbeh, on the road to Baghan and Bandar-Daiyer. These en-echelon, non-continuous segmented fissures do not show the displacement consistent with the fault mechanism (compressional with a strike slip movement); however, it is mostly a vertical displacement in most of segment, with some surface strike slip movements (not systematic in the same direction). The segments were located about 1 km distant from the Jashak Salt Diapir and it may be that the salt layers are effective in conducting the rupture to the alluvium surface. Most of the buildings damaged in this earthquake were adobe buildings, made of heavy material and constructed in the last 50 years. First aid was delivered to the approximately 10,000 inhabitants in the epicentral area on the first night by Iranian Navy forces and by the Iranian Red Crescent. Food (cold, packed and cooked) was delivered on second day after the earthquake. Temporary shelters were put up in the first week after the quake when the removal of debris using heavy machines was ongoing.
