Journal of Seismology and Earthquake Engineering
Volume:15 Issue: 1, Spring 2013

The Bam fault zone is a major active fault zone in southeastern Iran. Geomorphic evidence indicates that it has been responsible for repeated faulting events since late Pleistocene. The December 26, 2003 Bam earthquake was associated with two fresh surface ruptures 5 km apart trending north-south and a 2 km wide zone of hairline fractures developed between the two main ruptures in north Bam. The amount of slip along the surface ruptures ranges between 0.5-5.5 cm across the zone. The whole system of fresh ruptures associated with the Bam earthquake is not direct manifestations of the earthquake fault but are secondary structures such as synthetic shears (Reidel shears), mole tracks and oblique grabens which are strongly indicative of right-lateral motion along principal displacement zone in the earthquake source. This is compatible with the focal mechanism solutions of the Bam earthquake and fault displacements during the late Pleistocene.

A waveform inversion algorithm, based on least square method, has been applied to the P and S waves of the 26 December 2003 Bam earthquake. The aftershocks of this event distributed along a narrow zone (approximately 20km) in N-S direction. In this research, estimates of centroid depth, seismic moment, and source mechanism have been obtained. The source mechanism derived from the inversion of long period body waves revealed that two events occurred on N-S trending strike-slip fault with a thrust component. According to the source model estimated in this study, the Bam earthquake was a multiple event. The rupture following the first event started at a depth of about 8km. However depth of the second event is about 10km. The total seismic moment estimated from inversion processes is 8.34×1018Nm. The seismic moment of the second event is less than the first one (the seismic moment of second event is calculated as 2.34×1017Nm). The pulse duration of main shock and the second event was determined from source time function and it is 1.7s and 0.8s respectively. Corner frequency and source radius have been calculated for main shock and the second event by using pulse duration. The range of corner frequency and source radius are from 0.187Hz -0.397Hz and 5.47km- 2.57km for main shock and second event, respectively.

From 29 December to 30 January, a dense seismological network of 20 stations surrounding the epicentral area of the 26 December 2003 Bam earthquake was installed to study the seismic activity that took place after the main shock. The aftershock distribution is consistent with a 30 km north-south striking fault. The focal depths distribution shows a nearly vertical alignment of aftershocks located between 6 to 20 km depth. The focal mechanism solutions indicate right lateral strike slip faulting on N-S trending fault, parallel to the Bam fault trace. However, there is a small offset of about 5km westward between the Bam fault trace and the aftershocks distribution.

The Bam earthquake of 26 December 2003 (Mw6.5) occurred at 01:56:56 (GMT, 05:26:56 local time) around the city of Bam in the southeast of Iran. The Bam earthquake of 26/12/2003 (Mw6.5) has demolished the city of Bam, having a population of about 100000 at the time of the earthquake. The Bam fault-which was mapped before the event on the geological maps-has been reactivated during the 26/12/2003 earthquake. It seems that a length of about 10km(at the surface) of this fault has been reactivated, where it passed exactly from the east of the city of Bam. The fault has a slope towards the west and the focus of the event was located close to the residentialarea (almost beneath the city of Bam). This caused a great damage in the macroseismic epicentral zone; however the strong motions have been attenuated very rapidly, specially towards the east-and west (fault normal) direction. The vertical directivity effects caused the amplification of the low frequency motions in the fault-normal direction as well as the greater amplitude of the motion on the vertical direction. Two strong phases of energy are seen on the accelerograms. The first comprises of a starting sub-event with right-lateral strike slip mechanism which is located south of Bam. The mechanism of the second sub-event is reverse mechanism. The comparison of observed and simulated ground motion indicates that rupture started at a depth of 8km, south of Bam and propagated toward north.

This paper describes the geotechnical instabilities such as landslide, liquefaction, and ground subsidence caused by the Bam earthquake. Based on the results of geotechnical investigations, after the Bam earthquake, land subsidence due to collapse of Qanats (underground irrigation tunnels), local toppling, and block slides along riverbanks or man-made channels were the most dominant geotechnical instabilities of the event. These effects will be introduced and discussed in this paper and the distribution of them will be presented based on the study of aerial photos and site investigations. In addition, the geological setting of the area based on field investigations and evaluation of some geophysical data will be discussed.

After the devastating earthquake of 26 December 2003 in Bam, a discipline was followed to prepare a preliminary site effect microzonation map for the city. Seismic hazard studies for two return periods, geological studies accompanied by geophysical surveys and aftershock and microtremor measurements were carried out to provide site classification and PGA distribution maps. The results of this study show that reasonable agreements exist between the 2475 years PGA distribution map and the damage distribution map for the recent earthquake. The 475 years PGA microzonation maps could also be used as a preliminary useful hint in reconstruction and urban planning of the totally destroyed city.

A procedure developed for quick inspection of buildings in earthquake damaged areas of Bam by a group of volunteer engineers is introduced. The procedure is applied to 550 masonry, steel and reinforced concrete buildings. Distribution and statistics of the buildings characteristics such as their use, number of stories, penthouse and stairs damages, type of material and structural systems and type of diaphragms are determined. The information has provided important data about the design, detailing and construction deficiencies of common types of buildings in Bam.

The post earthquake investigations of the 26 December 2003 Bam-Iran earthquake were conducted by the Joint Reconnaissance Team of the Architectural Institute of Japan (AIJ), the Japan Society for Civil Engineers (JSCE), the Japan Association for Earthquake Engineering (JAEE) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in collaboration with the International Institute of Earthquake Engineering and Seismology (IIEES). This paper reports the results of the AIJ team on damage evaluation of the buildings around the Bam strong motion station operated by the Building and Housing Research Center (BHRC). The seismic capacity of damaged buildings was approximately estimated. The results show that many residential houses in the investigated area were seismically vulnerable structures such as adobe and simple masonry structures. Poor construction quality was also found in some of the investigated buildings designed according to the current Iranian seismic code. Moreover, good correlation between wall area ratio and damage levels was observed. Therefore, wall area ratio may be applicable for evaluating the seismic capacity and screening retrofit candidates.

Every earthquake provides new lessons for the earthquake engineering profession. The widespread damage to welded connections in steel structures was one of the major overall lessons of the Bam earthquake of December 26, 2003. The brittle nature of the fractures detected in weakly welded steel bracing connections, essentially invalidated the design approaches and code provisions based on «ductile» structural response. This paper reviews the performance of steel braced buildings during the Bam earthquake and the implications for design practice. The results can be used to develop and verify reliable and cost-effective methods for the inspection, evaluation, repair, and rehabilitation of similar existing steel buildings.

Collapse of non-engineered roofs and floor slabs during the Bam earthquake of December 2003 was the single major contributor to the large fatalities during that earthquake. Different floor systems of buildings in the city of Bam can be categorised into three types namely; the traditional masonry dome or vault, the steel I-beam jack arch system and the concrete beam-hollow block system. In this paper the seismic performance of each type of flooring as observed after the Bam earthquake is discussed and their points of weakness and strength are highlighted. Also the poor seismic performance of the traditional dome and vault roofs and the unanchored jack arch slabs are noted and the seismic merits of the anchored jack arch slabs and concrete beam-hollow block slabs are discussed.

The Arg-e Bam is a remarkable example of earthen architecture and construction that was heavily damaged in the Bam, Iran earthquake of 26 December 2003. This paper presents the hypothesis that the collapse of the walls was caused largely by a combination of the effects of (1) the additive changes made to the walls, particularly in recent restorations resulting in variations in the density and response to vibrations of different layers of unfired earth construction in the walls, and (2) extensive damage from termites and loss of the cohesion of the clay from degradation and excessive drying out, all of which interacted with the earthquake vibrations of unusually high frequency in such a way that many walls effectively burst from the subsidence of their clay internal cores. Concern is raised about the possibility of similar risks to other earthen monumental structures from future earthquakes.

At 5:26 am local time, Friday, December 26, 2003, an earthquake with moment magnitude 6.5 hit the city of Bam in southeast Iran. The earthquake caused more than 26,000 deaths, 30,000 injuries, and left 70,000 homeless. It caused extensive damage to residential and commercial buildings and emergency response facilities. In contrast to the inflicted human loss and suffering and extended building damage, lifeline systems, although damaged, performed much better. Transportation systems, i.e., roads, bridges, railways, and the airport, although slightly to moderately damaged, were generally operational soon after the earthquake to support emergency response and recovery effort. There were several breaks in the water distribution systems and minor damage to deep wells. However, the traditional qanat systems, which bring water from foothills tens of kilometers away via underground tunnels, were mostly damaged. The Bam area is served via connection to countrywide electric grid system. There was little damage to high voltage transmission lines and towers and minor damage to electric equipment in the main substation. Numerous concrete poles were damaged in the distribution system. There was nonstructural damage to telecom central offices. The main reason for the good performance of the lifeline facilities was that most of them are located outside the zone that was heavily damaged. Another reason is that they are newer facilities and in general more engineering has been used in lifeline facilities design and construction when compared with that for residential buildings.

Regarding the importance of the nonstructural elements in the vulnerability of buildings, and the extensive damages of some of these elements in recent earthquakes, particularly the Bam event, in this paper at first the characteristics of nonstructural elements are briefly reviewed, with emphasis on the Iranian buildings; then the seismic design, vulnerability, and upgrading of these elements are explained and discussed as a state-of-the-art review; and finally, the results of a thorough survey performed on the behavior of and the damages sustained by these elements, particularly the architectural ones, in the city of Bam because of the December26, 2003 earthquake are presented. Finally, based on the results of this survey some recommendations are made which can be useful for modification of the «Guidelines for the Seismic Retrofit of the Existing Buildings», which is used presently in the country as the only official reference in this regard.

On 26 December 2003 an earthquake of magnitude Ms= 6. 5 with a focal depth of about 8km occurred in southeastern Iran. The earthquake caused intense ground shaking throughout the affected area. Special structures such as on-grade steel oil tanks، elevated tanks، and industrial equipment were damaged during the earthquake. This paper presents the results of an investigation of the behavior of these special structures in Bam. Strong motion characteristics as recorded by accelerograms are discussed، as well as the failure modes of structures and components located within the affected area. An investigation into the response of an electrical transformer was carried out as a case study of a simple system.

May, 2004 the «Learning from Earthquakes» program of the Earthquake Engineering Research Institute sent a team of researchers on a reconnaissance mission to Iran and the site of the Bam earthquake (December 26, 2003). The purpose of this team was to study social science and policy aspects of the earthquake impact, relief and recovery phases. Interviews were conducted with a wide range of stakeholder groups including victims and those responsible for public and private recovery activities. Observations were collected related to transitional housing, mental health, economic and social recovery and the planning process for permanent reconstruction. Particular attention was paid to innovative programs and policies developed in response to this earthquake disaster.

After the earthquake on 26 December 2003 with magnitude 6.3 which struck the historic city of Bam and its surrounding villages and took the lives of nearly 26,500 people, left over 25,000 injured and about 75,000 homeless; the United Nations agencies in the Islamic Republic of Iran have worked closely with the Government to respond to the immediate needs of the affected people, by undertaking a rapid needs assessment and launching a Flash Appeal to address the urgent and immediate needs of the affected population, and to facilitate a smooth transition from the immediate rescue and relief phase to a medium and long-term reconstruction and recovery phase. The UN has committed itself to supporting the Government not only in the provision of short-term relief, but also in long-term reconstruction, recovery and risk reduction. UN Secretary-General Kofi Annan offered support for an international conference on the reconstruction of Bam as well as organizing an international workshop on earthquake disaster risk management. Recognizing the value of a concerted UN approach that complements the Government''s reconstruction and disaster risk reduction efforts, the UN System in consultation with its national and international partners has prepared a strategy document, using methods of social research such as participant observation, case studies, the use of key informants, group discussions and individual in-depth interviews. The strategy builds on past efforts of the UN System in the Iran and on the UN Flash Appeal of 8 January 2004. It outlines UN support to the Government of Iran for reconstruction, rehabilitation and risk reduction over the next five years, and details specific activities in the short, medium and long term.

This paper gives a brief explanation of the earthquake in Bam, casualties, as well as a report on rescue and relief operations, emergency shelters, temporary housing, and the country’s plan for the reconstruction of the city, which includes, debris removal, rebuilding rural and urban residential and commercial units, reconstructing state and public buildings and facilities, schools, rural and urban water aqueducts and grid, establishing sewerage system, power network, and telecommunication system, supplying orchards and farmlands with water, renovating industries, reviving cultural heritage particularly the historical Bam citadel and the like.