An earthquake struck the Kerman province of southeastern Iran at 01:56 UTC (5:26 am Iran Standard Time) on December 26, 2003. The Mw 6.6 (Ms 6.8–7.0) strike-slip shock had a maximum Mercalli intensity of X (Extreme). The earthquake was particularly destructive in Bam and Baravat, with 34,000 fatalities and 200,000 injuries officially reported. It was the deadliest natural disaster globally since the 1999 Vargas tragedy. The effects of the earthquake were exacerbated by the use of mud brick as the standard construction medium; many of the area's structures did not comply with earthquake regulations set in 1989.
Following the earthquake the U.S. offered direct humanitarian assistance to Iran and in return the state promised to comply with an agreement with the International Atomic Energy Agency which supports greater monitoring of its nuclear interests. In total a reported 44 countries sent in personnel to assist in relief operations and 60 countries offered assistance.
Following the earthquake, the Iranian government seriously considered moving the capital of Tehran in fear of an earthquake occurring there. The earthquake had a psychological impact on many of the victims for years afterwards. A new institutional framework in Iran was established to address problems of urban planning and to reconstruct the city of Bam in compliance with strict seismic regulations. This process marked a turning point, as government ministers and international organizations collaborated under this framework with local engineers and local people to organize the systematic rebuilding of the city.
Iran suffers from frequent earthquakes, with minor quakes occurring almost daily. This earthquake occurred as a result of stresses generated by movement of one tectonic plate, the Arabian plate, moving northward against another, the Eurasian plate, at approximately 3 centimetres (1 in) per year. The Earth's crust deforms in response to the plate motion in a broad zone spanning the width of Iran and extending north into Turkmenistan. Earthquakes occur as the result of reverse faulting and strike-slip faulting in the zone of deformation.
The preliminary analysis of the pattern of seismic-waves radiating from December 26, 2003, earthquake was consistent with the earthquake having been caused by right-lateral strike-slip motion on a north–south oriented fault. The earthquake occurred in a region within which major north–south, right-lateral, strike-slip faults had been previously mapped, and the epicenter is near the previously mapped, north–south oriented Bam Fault. However, field investigations will be necessary to find if the earthquake occurred on the Bam Fault or on another. The Bam earthquake is 100 kilometres (62 mi) south of the destructive earthquakes of June 11, 1981 (magnitude 6.6, approximately 3,000 deaths) and July 28, 1981 (magnitude 7.3, approximately 1,500 deaths). These earthquakes were caused by a combination of reverse-motion and strike-slip motion on the north–south oriented Gowk fault.
Bam had a pre-earthquake population of between 97,000 and 142,376. It is one of the most popular tourism areas of Iran, one of its most popular attractions being its 2000-year-old mud-brick Bam Citadel. During the Safavid dynasty (1501–1736) Bam was a large trading hub due to its location on the Silk Road. It gradually declined in significance after the Afghans invaded in 1722, serving as an army camp until its abandonment in 1932. The city became a tourist attraction in 1953, when restoration of Bam's Old Quarter began.
There was little earthquake education in Iran although the International Institute of Earthquake Engineering and Seismology established a Public Education Department in 1990 to improve "the safety, preventing, and preparedness culture against the earthquake among all groups of the society". In October 2003, Bahram Akasheh, professor of geophysics at Tehran University, called the effects of public ignorance about earthquakes "poisonous".
According to the United States Geological Survey (USGS), the earthquake had a moment magnitude (Mwc) of 6.6, and was located 12 km (7.5 mi) southwest of Baravat and 13 km (8.1 mi) south-southwest of Bam. On the seismic magnitude scale (Ms), it measured 6.8 and 7.0, according to the National Geophysical Data Center and the China Earthquake Administration, respectively. It struck at 01:56:52 UTC (05:26:52 IST) on 26 December 2003, at a depth of 15 km (9.3 mi). It had a maximum Modified Mercalli intensity (MMI) of X (Extreme); at Bam, the intensity was MMI IX (Violent), with shaking of MMI VIII (Severe) estimated at Baravat and V (Moderate) at Kerman. Bam also recorded a maximum peak ground acceleration (pga) of 0.98 g. It is believed to be the largest earthquake to hit the Bam area in more than 2,000 years. The day before, on 25 December, two foreshocks struck Bam and were felt by residents of the city at 15:00 and 22:00 IST respectively. The following day, a third foreshock struck at 04:33, followed by the mainshock almost an hour later. At least 2,789 aftershocks were recorded by March 2004, the strongest measuring mb 5.1, which struck at 06:36 IST.
The rupture length of the earthquake was estimated to be around 24 km (15 mi). More than half of the quake was produced from its southern segment of approximately 13 kilometres (8 mi), where the slip reached a maximum of up to 2.7 metres (8.9 ft) resulting in a large stress drop of at least 6 MPa. Optical remote sensing data shows that the Bam fault is not a single fault but consists of a 4–5 km (2.5–3.1 mi) wide fault system with the main branch running between the cities of Bam and Baravat. The fault ruptured by the Bam earthquake is believed to stretch the along northwest branch of this fault system from Bam southward. Based on these results, scientists suggest that the Bam earthquake ruptured a hidden fault and that in this process an unusually strong asperity was involved, causing the widespread devastation of the tremor.
For years, the death toll was heavily disputed. Initially, local media estimated up to 70,000 fatalities, before a death toll of 56,230 was confirmed on 17 January 2004, a figure later revised to 26,271 deaths by the Statistical Center of Iran. The BBC added that confusion regarding the true death toll arose as rescue groups had counted the bodies of victims twice. On 26 December 2020, exactly 17 years after the earthquake, Iran's Crisis Management Organization confirmed 34,000 fatalities and 200,000 injuries. In terms of human loss the quake was the worst to occur in Iranian history. The BBC reported that a large number of victims were crushed while sleeping. At least 10,000 students and 1,200 teachers were among the dead. This caused a significant problem for the local education system. At least 5,054 children were orphaned and 400 people were left disabled in the aftermath of the earthquake.
Up to 95% of buildings and infrastructure in the Bam area were either damaged or destroyed, with 90% of structures severely damaged or collapsed and 70% of houses being completely destroyed, plus 70–90% of Bam's residential areas. Some areas of the city were entirely reduced to rubble, while all 122 health centers and three hospitals collapsed or were badly damaged. Not a single house was standing in nearby Baravat, where 1,112 deaths, 36 missing and 578 injuries were recorded. In total, approximately 53,000 buildings, including 25,000 in Bam, 24,000 in villages within a 10 km radius of the city and 4,000 in Baravat were destroyed. Most of the destruction was concentrated within a 16 kilometres (9.9 mi) radius around Bam. Electricity and water supplies were cut by the earthquake. An important regional center during the 16th and 17th centuries, Bam contained many buildings that were not constructed to survive such ruptures. Many houses in Bam were homemade, and its owners did not use skilled labor or proper building materials to resist earthquakes in the construction. These were often built in the traditional mud-brick style. Mohsen Aboutorabi, professor of architecture at the University of Central England, demonstrated the lack of good building materials by banging two bricks together in Bam, resulting in cracking. On the other hand, Iranian regulations laid down in the 1989 Iran seismic code were better enforced in high rise buildings and skyscrapers.