On August 11, 2012, at 4:53 pm local time, a magnitude 6.4 earthquake struck 60km (37 mi) north of the city of Tabriz in northwestern Iran. Eleven minutes later, a magnitude 6.3 aftershock hit near the original epicenter. More than 300 people died, 5,000 were injured, and 36,000 were made homeless. A magnitude 6.4 quake normally produces local property damage, some injuries, but very few fatalities. So why was a quake of this moderate magnitude so devastating?
The people who live in the villages of rural Iran build their houses today in the same way they have done for hundreds of years. The main building material is clay brick mixed with straw. A heavy roofs rests directly on the mud brick walls, not supported by beams or framing. When the region suffers a quake of even moderate strength, the shaking causes the roof to collapse and bring the walls down, killing, injuring, or trapping everyone inside.
The city of Tabriz, where some modern building practices are followed, had some damage and 45 fatalities. It was the villages in the mountainous areas surrounding Tabriz that were hit the hardest. According to Iranian officials, 130 villages were 70% to 90% destroyed, and 20 villages were completely leveled.
This scenario keeps repeating itself. In 2002, a 6.5 magnitude earthquake killed 261. In 2003, a 6.6 earthquake southeast of Tehran wiped out the entire city of Bam, killing 31,000. In 2005, a 6.4 magnitude quake killed 612. One solution to this problem might be for the Iranian government to take steps to help the rural villages build safer houses, and retrofit the older ones against the shaking that is sure to come in this earthquake-prone region.
The Zagros Fold & Thrust Belt (FTB) is a complex of fault lines that runs for 1,800km (1,200 mi) from southern Iran to the Greater Caucasus Mountains in the north. The Zagros marks the convergence of the Arabian and Eurasian tectonic plates, where the Arabian Plate constantly pushes north into the Eurasian Plate at 20mm (0.8 in) a year, putting great stress on the fault lines separating the two plates. When the pressure builds high enough, a fault line section releases, and the Arabian Plate slips under the continental Eurasian Plate in a sudden, violent motion that produces shaking over a wide area. Iran is one of the world’s most seismically active areas.