The Bam Earthquake of 26 December 2003

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Bam Earthquake of 26 December 2003 ICG Reconnaissance Mission

ICG report 2004-99-1 16 April 2004 Report prepared for and in cooperation with Geological Survey of Iran

Client: The Research Council of Norway Contact person: Are Birger CarlsonContract reference: SFF – ICG 146035/420

For International Centre for Geohazards Project Manager: Farrokh Nadim

Report prepared by: Farrokh Nadim (NGI) Conrad Lindholm (NORSAR)

Svein Remseth (NTNU) Arild Andresen (UiO) Masoud Moghtaderi-Zadeh (Risk

& Reliability Engineering) Work also carried out by: Eirik Tvedt (Statoil)

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Bam Earthquake of 26 December 2003 Report No.: 2004-99-1 Date: 2004.04.16 Rev.: - Rev. date: -ICG Reconnaissance Mission Page: 2

Summary

The devastating earthquake of 26 December 2003 claimed more than 43,000 lives in the city of Bam in southeast Iran, and left the majority of the Bam population homeless. The reason for this tragedy was an unfortunate combination of geological, social and human circumstances. The seismo-tectonic circumstances that contributed to the disaster were:

• The causative fault practically traversed the city of Bam. • The earthquake occurred at a shallow depth (only 10km below surface). • The fault rupture started south of Bam and propagated northwards. The

shaking was most severe in Bam at the northernmost point of the rupture. • The earthquake occurred on a fault and in a region that was not perceived

as being particularly seismically active. • It is possible that the normal component of fault displacement added

additional damaging power to the earthquake. Society also contributed to the disaster through the following factors:

• The residential buildings were completely inappropriate for a seismic region, being extremely vulnerable to earthquake shaking.

• The requirements of the Iranian Code of Practice for Seismic Resistant Design of Buildings were ignored or not enforced for residential buildings.

• The foreshocks were not regarded as serious warnings.

Another factor that contributed to the high death toll was the timing of the event. The earthquake occurred early in the morning when most people were still sleeping in their beds. The damage pattern was nearly symmetric about a line 3 km to the west of the surface expression of the Bam fault, and the damage attenuated rapidly with distance from this line (very little or no damage at distances greater than 4 km from the reference line!). The observations confirmed that well-designed structures would have survived with minor only damage the severe earthquake shaking levels experienced during the Bam earthquake. The industrial facilities around the city of Bam performed well and experienced very little damage, but this might have been due to their distance from the earthquake epicentre. In contrast, emergency facilities (hospitals, police and fire stations), schools and the university were destroyed and/or heavily damaged during the earthquake. With the exception of “qanats” (traditional subterranean irrigation channels), the lifelines performed surprisingly well during the earthquake. Only minor damage occurred to the city water system, electric systems, roads, the airport,

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railway, gas and petroleum stations, and telecommunications. This was mainly due to the distance of the critical facilities from the earthquake epicentre. However, out of the more than 60 qanat chains that served the twin cities of Bam and Baravat, only 4 survived the earthquake. The agricultural activities in the Bam area (mainly date tree gardens) are totally dependent on the water transported by these qanats from the foothills of Jebal-e-Barez mountains, tens of kilometres away. The importance of qanats to the livelihood of the people cannot be underestimated. The city of Bam is where it is because the fault that caused the earthquake also provided the conditions for the access to water for agricultural activities (daybreak of the qanats occurs on the surface expression of the Bam fault). A unique set of strong motion acceleration recordings were obtained at the Bam accelerograph station, operated by the Building and Housing Research Centre (BHRC) of Iran. Although the highest peak ground acceleration (nearly 1g) was recorded for the vertical component of the motion, the longitudinal component (fault-parallel motion in N-S direction) clearly had the largest energy flux, as well as the largest maximum velocity and maximum ground displacement. The response spectra of all three components of motion show a peak in the period range of 0.5 to 1.5 seconds. This is either due to the effects of the local soil response or related to the earthquake source function. The geotechnical effects of the earthquake were not significant. There was little evidence that site response effects played a major role in the damage pattern in the city. There were no reports of liquefaction and only minor sliding activity took place during the event. The earthquake created some sinkholes in and around Bam. The most serious geotechnical effect was the collapse of “qanats” in the vicinity of the surface expression of the Bam fault. Recommendations:

• The rebuilding of Bam must be done with application of simple but well proven anti-seismic design of residential buildings.

• The complete collapse of new residential buildings in Bam should be regarded as a warning to all other cities and villages in Iran where these building types are prevalent.

• Faults similar to the one traversing the city of Bam, and which have not shown activity for hundreds of years are likely to exist in many locations in Iran. A programme to map such faults would be an important step for future disaster mitigation.

• The correlation between access to water and proximity to earthquake-generating faults is a problem that needs to be studied further for other towns and villages around the margin of the Lut desert.

• The unfinished hospital in Bam appears to be a well-designed and constructed structure which performed well under the seismic loading. It should be finished and put into use, but a new design check should take into account that this is a structure of high importance class.



Contents

1 INTRODUCTION....................................................................................... 5

2 GEOLOGICAL SETTING ......................................................................... 7 2.1 The Bam fault .................................................................................... 8 2.2 ICG’s observations and interpretation ............................................... 9

3 SEISMOLOGY AND SEISMOTECTONIC............................................ 13 3.1 History of recent earthquakes .......................................................... 13 3.2 Main shock and aftershocks of the 26 December 2003 event ......... 15 3.3 Strong ground motion recording...................................................... 20

4 PERFORMANCE OF BUILDINGS......................................................... 26 4.1 Typical building types in Bam......................................................... 26 4.2 Damage survey ................................................................................ 28 4.3 Proposed reference line for damage pattern .................................... 45 4.4 Performance of various types of buildings ...................................... 45 4.5 Emergency facilities ........................................................................ 47

5 GEOTECHNICAL EFFECTS .................................................................. 49

6 INDUSTRIAL FACILITIES AND LIFELINES ...................................... 53 6.1 Industrial facilities ........................................................................... 53 6.2 Water systems .................................................................................. 57 6.3 Electricity......................................................................................... 64 6.4 Roads ............................................................................................... 68 6.5 Airport.............................................................................................. 71 6.6 Railway ............................................................................................ 73 6.7 Gas and Petroleum........................................................................... 74 6.8 Communications .............................................................................. 74

7 CONCLUSIONS....................................................................................... 76

8 ACKNOWLEDGMENTS......................................................................... 78

9 REFERENCES.......................................................................................... 78 Review and reference page



1 INTRODUCTION

On 26 December 2003 at 01:56 GMT (05:26 local time), an earthquake devastated the city of Bam. Bam is located in the margin of Kavir-e-Lut desert in the south-eastern part of Iran (Fig. 1.1). The city had a population of around 150,000 prior to the earthquake.

Fig. 1.1 Left: Geographical setting of Bam (from www.lonelyplanet.com) and mechanism of recent earthquakes in the south-eastern part of Iran, star shows the epicentre of the earthquake on 26 December 2003 (from www.usgs.gov).

The earthquake had a magnitude of Mw = 6.5 (USGS) and an epicentre location of 29.00N, 58.34 E (USGS). Focal depth was estimated to be about 10km. At the time of the writing of this report, the official death toll is 43,000; however, a figure of 50,000 is regarded as more realistic. Furthermore, over 50,000 people were injured and about 100,000 people became homeless by this event. The earthquake destroyed almost 70 percent of the conjugated cities of Bam and Baravat and the historical castle of Arg-e-Bam (2,000 – 2,500 years old mud-brick citadel – the largest mud-brick construction in the world prior to the earthquake). By invitation of the Geological Survey of Iran, GSI (www.gsi.org.ir), the Centre of Excellence International Centre for Geohazards, ICG (www.geohazards.no), sent a team of experts on a post-earthquake reconnaissance mission to Bam in January 2004. The ICG team consisted of:


http://www.usgs.gov/

http://www.gsi.org.ir/

http://www.geohazards.no/


• Dr Farrokh Nadim, ICG / NGI (Team Leader, geotechnics) • Dr Conrad Lindholm, ICG / NORSAR (seismology) • Prof. Svein Remseth, ICG / NTNU (structures) • Prof. Arild Andresen, ICG / University of Oslo (tectonics and geology) • Dr Masoud Moghtaderi-Zadeh, Consultant to ICG (lifelines and

industrial facilities) • Mr Eirik Tvedt, Statoil (earthquake engineering)

The ICG team was guided by the following team from GSI during the visit to Bam:

• Mr Mohammad J. Bolourchi, Head of Engineering Geology Department, GSI-Tehran (Team Leader, geology)

• Mr Kourosh Latifi, GSI-Tehran (seismo-tectonics) • Mr Mohammad Mohammadi-Ara (geology, GSI-Kerman) • Mr Ali Rashidi (geology, GSI-Kerman)

The mission started with a full-day briefing at the GSI office in Tehran on 24 January 2004. The observations and conclusions of the GSI team that had spent about 10 days in Bam immediately after the earthquake were presented to the ICG team. The ICG team was requested to focus on the following tasks during their visit to Bam:

• Confirm or modify the conclusions drawn by the GSI post-earthquake team.

• Supplement the GSI with additional observations regarding the performance of buildings and lifelines.

• Inspect the hospital building that was partially constructed at the time of the earthquake and evaluate whether the building could be completed after repairs.

In the afternoon of 24 Jan., the ICG team visited the International Institute of Earthquake Engineering and Seismology, IIEES (www.iiees.ac.ir). Dr M. Zare, head of the Engineering Seismology Dept. of IIEES informed the team about the post-earthquake activities of IIEES and their measurements of the aftershocks through the deployment of seismic stations around Bam immediately following the earthquake. The ICG/GSI team travelled to Bam on 25 Jan. and spent 3 days in the area. Before returning to Norway, the team presented their preliminary findings in a 2-hour presentation at GSI on 28 Jan. The presentation was open to the general public and was well attended by both GSI employees and guests from other organisations (IIEES and others). The observations and findings of the ICG/GSI team are presented below.


http://www.iiees.ac.ir/


2 GEOLOGICAL SETTING

Tectonically Iran is located in the main part of the Alpine-Himalaya orogenic belt and divided to subdivisions, which were introduced by Alavi (1991) in the Tectonic Map of the Middle East (Fig. 2.1). One of the main tectonic features is the Central Iranian Block which consists of the Yazd, Poshte Badam, Tabas and Lut blocks. The city of Bam is located in the southern part of the Lut Block. The borders between these blocks are strike slip faults, and as seen in Fig. 2.1 the blocks have been subject to large scale counter-clockwise rotation.

Fig. 2.1 Tectonic setting of Iran



Five different lithologies can be observed in the main geological formations of the area including: a) recent Quaternary alluvium, b) late Quaternary sandstones and siltstones, c) Palaeogene sedimentary rocks, d) Eocene volcanic rocks, and e) intrusive igneous rocks (Granodiorite). The thickness of the sediments having low to medium compaction is about 200 metres. The effects of deep erosion can be observed in these sediments. The city of Bam is located southeast of Kerman, in the south-eastern part of Iran (see Fig. 1.1). The area of the city is about 5,400 hectares having a smooth topography and morphology. The altitude of the city is approximately 1,050 metres above sea level. Due to small amount of rainfall and scarcity of surface water, the main sources of drinking and agricultural water for Bam and its vicinity are underground water resources, such as deep wells, and underground irrigation tunnels (qanats).

2.1 The Bam fault

The Bam fault, a 50km long right-lateral strike slip fault with north-south trend, is the main tectonic feature of the area (Fig. 2.2). It was the Bam fault that ruptured during the 26 Dec. 2003 earthquake. It was not known as being active in historical times, and it is primarily traceable through gently elevated terrains (due to a small compressive component of the fault). The fault trace itself is buried under the thick sediments. If one assumes that the Andoohjerd fault is the continuation of the Bam fault, then the total length of the fault will be over 150km. The Andoohjerd fault has evidences of warm springs, like travertine and argonite.



Fig. 2.2 Satellite map of the area – Bam and Golbaft faults are indicated. The surface features of this fault are found in an area comprised of old Quaternary sediments on younger sedimentary layers at east of Bam. As a result, the old Quaternary sediments formed a hilly morphology that has been cut by some drainage systems in the area, which have made several deep channels prone to landslide.

2.2 ICG’s observations and interpretation

2.2.1 The Bam Lineament

The Bam Fault appears as a distinct N-S striking linear feature on both aerial photographs and satellite images in the area between Bam and Baravat. Field examination of this lineament shows it to correspond to a marked N-S striking elevation step in the topography where the eastern part is 20 to 25m lower than the western part. The lineament appears to be covered by younger flood-plain deposits to the south and recent alluvial fan deposits to the north, where the bedrock (vulcanite) is exposed locally. This morphological feature or lineament described above has traditionally been interpreted as a fault scarp associated with an N-S striking high angle reverse fault (Bam Fault). During our short visit to Bam we were able make two traverses in two gullies crossing the lineament. In neither of the traverses did we observe convincing evidences, like minor faults, that the lineament represents a faults scarp. We observed instead that the sub-horizontally interbedded sandstones and



conglomerates (alluvial fan deposits?) of the uplifted western part change orientation as one is approaching the lineament or step in topography. Along the lineament itself the interbedded sandstones and conglomerates dip as much as 10° towards east (Fig. 2.3). On the eastern side of the lineament one finds flat lying, younger, fine-grained sediment (flood-plain deposits?) lapping onto the deformed and tilted alluvial fan deposits. Based on these field-relationships we interpret the Bam lineament to be an east-facing monocline in the area between Bam and Baravat, developed above a steep reverse fault (the Bam Fault) (Fig 2.4).

2.2.2 Kinematics

The fault-plane solution shows that the Bam earthquake is associated with a steeply-dipping, right lateral strike-slip fault (Fig. 2.6). The surface cracks found during the survey were generally small (maximum a few centimetres wide), and they were not carrying any distinct rupture characteristics. Most of them were small-scale reverse faults or pressure ridges and open fractures (Fig. 2.8). The surface ruptures found appear within the desert north of Bam, and in a narrow zone separating Bam and Bavarat.

Fig. 2.3 Tilted beds along the Bam lineament.



Fig. 2.4 Monocline above a steep reverse fault.

Fig. 2.6 The earthquake rupture on a steeply-dipping, right lateral strike-slip

fault.



Fig. 2.7 Surface fault rapture that indicates right lateral strike slip faulting

(from Geological Survey of Iran’s report).

Fig. 2.8 Typical surface rupture features (small-scale reverse faults or

pressure ridges) observed north of Bam.



3 SEISMOLOGY AND SEISMOTECTONIC

3.1 History of recent earthquakes

The historical seismicity from the larger region around Bam is shown on Fig. 3.1. Large parts of Iran are seismically very active. However, the Bam region was not regarded as belonging to the most active zones. The main reasoning behind this assumption was that a) no historical damaging earthquake had previously been reported from Bam, and b) the Arg-e-Bam citadel was an indirect evidence of the lack of damaging earthquakes. The youngest parts of the citadel dated approximately to 400 years ago, while the oldest parts were over 2000 years old. Arg-e-Bam had, to the best of our knowledge, not been damaged previously by any earthquake. The historically low seismic activity around Bam is reflected in the predicted accelerations of around 0.30g at 10% probability in 500 years (the GSHAP study), which is relatively moderate. Three large earthquakes have struck the region north of Bam (on the Gowk fault) over the last decades (see Fig. 3.2):

• The Golbaf earthquake of 11 June 1981, Ms=6.6; Estimated 3000 casualties

• The Sirch earthquake of 28 July 1981, Ms=7.0; Estimated 1500 casualties

• The North Golbaf (Fandogha) earthquake of 14 March 1998, Mw=6.6

The trends of the main faults (including the Bam fault) in this region are north-south, and NW-SE (Figs 2.2 and 3.1, which are intersected by a fault in the western Lut block. The NW-SE faults (Kuhbanan and Ravar faults) and the north-south faults (Nayband, Chahar-Farsakh, Anduhjerd, Gowk, Sarvestan and Bam faults) define the border of the north-south structures in the Lut area with the NW-SE structures. The Gowk fault system is recognisable for its surface ruptures during the 1981, 1989 and 1998 earthquakes as well as a hot spring system.



Fig. 3.1 Historical seismicity of the larger region around Bam. Ref.: International Institute of Earthquake Engineering and Seismology (IIEES).

The Golbaf earthquake of 11/06/1981 struck the region of Golbaf in the southern part of the Golbaf valley (with the strike of N5-15E). This earthquake, which was associated with a fault rupture along the Gowk fault, caused 1071 fatalities. The event caused great damage in the Golbaf region. The Sirch earthquake of 28/07/1981 occurred 49 days after the Golbaf earthquake and caused 877 life losses. It seems that it was originated as the secondary faulting along the Gowk fault (N-S trend) or the triggering of the rupture from activation of the Gowk fault in the hidden continuation of the Kuhbanan fault (NW-SE trend), in their intersection zone. Such a situation might be the reason for the great earthquakes around Sirch in 1877 and 1981 (both with magnitudes greater than 7.0). The South Golbaf earthquake of 20/11/1989 caused 4 fatalities and 45 injured and some damages in Golbaf. Some surface faulting and folding have been reported to be related to this event. The North Golbaf earthquake of 14/3/1998 caused 5 fatalities and 50 injuries, and was associated with surface faulting (about 20km length) in northern Golbaf. The focal mechanism of these earthquakes shows the compressional and strike slip mechanisms along the Gowk and Kuhbanan fault systems.



Fig. 3.2 Recent major earthquakes in the region.

3.2 Main shock and aftershocks of the 26 December 2003 event

The Bam earthquake hit on Friday, 26 December 2003 at 01:56 (GMT), corresponding to 05:26 A.M. local time. It occurred while most people were still sleeping, and this explains the extraordinarily high death toll for this event. According to eyewitness accounts, the night before the main earthquake the local population felt at least 3 foreshocks, partly accompanied by rumbling noises, and a bluish light (possibly from electrical wires).


The Bam Earthquake of 26 December 2003

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