The Bam earthquake of December 26, 2003 (Mw6.5) occurred around the city of Bam in southeast Iran. Because the earthquake happened early in the morning at 01: 56: 56 (GMT, 05: 26: 26 local time), most of the reported 43,100 victims were killed in their dwellings. In Iran, there are dense strong ground motion networks for describing the seismological features of earthquakes, but very sparse networks for damage distribution analysis. Actually, damage differed from street block to street block, and only one seismometer was available in the city. Measuring traces of intense shakes remaining in structures, which are seen everywhere and have common features, can be very effective. The authors used utility poles in Bam for this structure. This report provides a spatial distribution of strains induced in these poles, and compares them with damage distribution in the city

Alireza Farahani

Hossein Tahghighi

Konagai Kazuo

Meguro Kimiro

Mohammad Keshavarz

Paola Mayorca

Takashima Masasuke

Yoshimi Masayuki

Yoshimura Miho

アリレザ ファラハニ

パオラ マヨルカ

ホセイン ターギギ

モハマド ケシャバルズ

吉村 美保

吉見 雅行

小長井 一男

目黒 公郎

高島 正典

UTokyo Repository

Strain Induced in Cracked Utility Poles and Damage to
Dwellings from the Dec ,0, ,**-, Bam Earthquake
Kazuo Konagai+*, Masayuki Yoshimi,, Kimiro Meguro+, Miho Yoshimura+,
Paola Mayorca+, Masasuke Takashima+, Alireza Farahani+, Hossein Tahghighi+
and Mohammad Keshavarz-
+ Institute of Industrial Science, The Univ. of Tokyo
, Active Fault Research Center, National Inst., Advanced Industrial Science and Technology
- The International Institute of Earthquake Engineering and Seismology, Iran
Abstract
The Bam earthquake of December ,0, ,**- (Mw0./) occurred around the city of Bam in southeast
Iran. Because the earthquake happened early in the morning at *+ : /0 : /0 (GMT, */ : ,0 : ,0 local
time), most of the reported .-,+** victims were killed in their dwellings. In Iran, there are dense
strong ground motion networks for describing the seismological features of earthquakes, but very
sparse networks for damage distribution analysis. Actually, damage di#ered from street block to
street block, and only one seismometer was available in the city. Measuring traces of intense shakes
remaining in structures, which are seen everywhere and have common features, can be very
e#ective. The authors used utility poles in Bam for this structure. This report provides a spatial
distribution of strains induced in these poles, and compares them with damage distribution in the
city.
Key words : Bam earthquake, local site e#ect, utility poles, microtremors, adobe dwellings
+. Introduction
An intense earthquake occurred in southeastern
Iran at / : ,2 local time, December ,0, ,**-. Although
the moderate moment magnitude of 0./ (Building and
Housing Research Center, Iran) - 0.0 (USGS) calcu-
lated for this earthquake was not surprisingly large
when contrasted with major earthquakes that have
occurred in this country, Bam, an oasis city in a
desert, was ravaged. About .-,+** people were re-
portedly killed and -*,*** injured, making this earth-
quake the worst Iran has experienced in the past
century.
The city had about +**,*** residents according to
o$cial ﬁgures. Shortly after the earthquake, o$cials
announced that the possible deaths would number
,2,***. The number was revised downward to ,0,/**
on January -, but as rescue crews continued to pull
out dead bodies from debris, the death toll increased.
On Jan. +/ the o$cial estimates put the number of
casualties at between -*,*** and -/,***, and to date
the death toll has increased to .-,+**. Because the
earthquake happened quite early in the morning, the
majority of the casualties were in their dwellings,
mostly adobe, unreinforced and/or conﬁned ma-
sonry structures.
Because the e#ects of the earthquake were quan-
titatively serious and broad in scope, several organi-
zations in Japan dispatched teams. They included
the Japan Association for Earthquake Engineering
(JAEE), Japan Society of Civil Engineers (JSCE), and
the Ministry of Education, Culture, Sports, Science
and Technology (MEX). The MEX team was made
up of several sub-teams with wide-ranging expertise.
After some discussions, a joint engineering team was
organized to undertake an e$cient reconnaissance
survey. Although the major counterpart organiza-
tion was the International Institute of Earthquake
Engineering and Seismology (IIEES), the Building
      
Bull. Earthq. Res. Inst.
Univ. Tokyo
Vol. 13 	,**. pp. /301
* e-mail : konagai@iis.u-tokyo.ac.jp (.0+ Komaba, Meguro-ku, Tokyo +/-2/*/, Japan)

 59 

and Housing Research Institute (BHRC) and the Uni-
versity of Tehran (UT) also collaborated during the
ﬁeld survey. The joint team made the ﬁrst and
second reconnaissance trips on Feb. +0/ and Feb. ,-
-March /, respectively, stressing the evaluation of
damage to dwellings and description of damage in
terms of possible intensity distribution, which might
have been a#ected by local and geological site condi-
tions.
,. Source Parameters and Geological Structure
Southeastern Iran is a region with widespread
active faults (Fig. + a) that basically take up a right-
lateral shear in this area. The Bam Earthquake,
measuring 0.0 on the Richter scale, occurred on De-
cember ,0, ,**- at */ : ,2 local time, with its epicenter
located at ,3.**.N, /2.--1E, on a predominantly
right-lateral strike-slip fault. The focal depth was
located 1 to +,km directly underneath Bam city
spreading west behind a pressure ridge formed along
Bam fault (Fig. +b). The presence of a pressure ridge
suggests that there are shortening (thrusting) com-
ponents associated with the strike-slip movement of
the fault.
Figure +b shows satellite imagery from LAND-
SAT (NASA, ,**.) covering Bam. A volcanic rock
outcrop can be seen just north of the city, which dips
to the south. The rock is cut in half by the Bam fault,
which extends from north to south. The ,-km-wide
pressure ridge has stopped sand, soil, and other sus-
Fig. +. Location of Bam and its satellite imagery : The Bam fault take-up is basically a right-lateral shear in this area.
However, some shortening components have been responsible for forming a pressure ridge along the fault. Bam city
is spread behind the pressure ridge on the hanging wall side. (Satellite imagery from LANDSAT, (NASA, ,**.),
October +, +333), Fault map from Walker et al. (,**-).
K. Konagai M. Yoshimi K. Meguro M. Yoshimura P. Mayorca M. Takashima A. Farahani H. Tahghighi M. Keshavarz
 60 
pended matters that rivers from mountains have
carried over the centuries. The area is thus rich in
underground water. Taking advantage of this, Bam,
as an old oasis city, has developed with no reported
great historic earthquakes before this event.
The city extends about 0 km from north to south
and 2 km from east to west on the hanging wall side.
The International Institute of Earthquake Engi-
neering and Seismology (IIEES) did seismic proﬁling
along a total of +* lines in the city after the earth-
quake. Bars in Fig. , show average soil proﬁles at
these lines. Alluvial soil thickly covers the mid- to
southern part of the city area, while the soil becomes
thinner as we go north. Fig. - shows inferred layer
boundaries of shear wave velocities +//m/s and 3**
m/s respectively, both showing rich variations of
soil proﬁle in Bam city.
-. Strains Remaining on Utility Poles
For oasis cities near active faults to be prepared
for possible future earthquakes, damage caused by
the Bam earthquake is discussed in terms of strong
ground motion features that dwellings have experi-
enced. However, as is often the case, damage di#ered
from street block to street block, and only one seis-
mometer was available in the city. In countries such
as Japan and Iran, which are ranked among the most
seismic hazard prone zones in the world, strong
ground motion networks are often very dense for
describing the seismological features of earthquakes,
but are very sparse for describing damage distribu-
tion, frustrating many attempts to learn lessons from
tragedies. Among possible breakthroughs, measur-
ing traces of intense shake remaining in structures,
which are seen everywhere and have common fea-
tures, can be very e#ective. The authors used utility
poles in Bam for this structure. Poles di#er in their
Fig. ,. Seismic soil proﬁling in Bam: Each mark with a circle at one end shows the line taken for seismic proﬁling. A
circle denotes the point where a blow was given. (Original data from IIEES).
Fig. -. Inferred layer boundaries of shear wave ve-
locities +//m/s and 3**m/s respectively.
Strain Induced in Cracked Utility Poles and Damage to Dwellings from the Dec ,0, ,**-, Bam Earthquake
 61 
dimensions from area to area, but a thin pole with
holes for climbing were the most widely used in the
city (Fig. .(a)), and thus, were chosen as the target.
To examine the dynamic features of this type of
pole, microtremors were measured at two poles (Fig.
. (b)). Their characteristics are summarized in Table
+. Bottom holes on P-, pole were ﬁlled in to prevent
theft.
A pair of --component velocity sensors was used
for the measurements, one on the ground and the
other strapped to each pole at a height of about +.* to
+./m above the ground. In each case, the X-axis was
taken along the transmission line. Tremors were
measured with poles a) subjected to ambient vibra-
tion, basically wind; b) striking in X-direction; and c)
striking in Y-direction.
Each time the history of the tremor was divided
into several +*.,. sec segments. Fourier spectra of all
segments were then calculated and averaged for
each time history. To obtain transfer functions in
the frequency domain, spectra measured on the pole
were divided by those on the ground.
Figure / shows the transfer function for P-+. It is
clear in Y-direction that there is little change of the
predominant periods between the ambient and hit
cases. In both cases, clear peaks are found at *.+*/
and *./1 sec, with the main di#erence being the peak
relative amplitudes. When the structure is hit, the
lower period amplitude becomes higher.
Poles exhibit quite di#erent vibration features in
the X-direction (Compare Figs. / (a) and / (b) with /
(c) and / (d)). As for ambient vibration cases, , peaks
at *.*1 and +.+* sec are distinguished among the oth-
ers at *.+2, *.,+, and *.0. When the structure is struck,
, clear peaks appear at *.+2 and *.,+ s, in addition to
*.*1 and +.+* s, but the *.0 s peak is not clearly seen,
suggesting that this peak is crosstalk from the Y-
component of the pole vibration.
Figure 0 shows the transfer functions for the P-,
pole. The functions have similar shapes to those for
the P-+ pole in all cases, suggesting that mortar ﬁlled
in the holes had little e#ect on the dynamic behavior
of the pole. Fig. 1 (a), (b) and (c) show X, Y, and Z
components of the pole vibration spectra. It is noted
Table +. Characteristics of the surveyed poles
Name Height
(m)
Remarks
P-+
P-,
040
040
Pole with hexagonal holes
Pole with hexagonal holes ﬁlled with
concrete
(a) 2m pole with holes and embedment depth of ,m.
(b) Poles P-+ and P-,.
Fig. .. Poles used in Bam.
K. Konagai M. Yoshimi K. Meguro M. Yoshimura P. Mayorca M. Takashima A. Farahani H. Tahghighi M. Keshavarz
 62 
that the spectra for X and Z components are similar
to each other, while the Y component exhibits some
di#erent shapes. Fig. 1 (d) shows X/Z and Y/Z spec-
tra ratios to highlight this feature. Assuming that
the vertical vibrations of the pole were mainly in-
duced by cable oscillations, it may be concluded that
a cable has an important e#ect on the pole’s motion
along the cable.
For this reason, crack openings on pole sides
without holes were taken to minimize the e#ects of
transmission lines, the cracks caused by the motion
of poles in the Y direction. For each pole, crack
openings were added up over about a ,m distance
near the lower pole end, and then all of the openings
were divided by the distance to obtain the average
strain remaining on the pole. A total of ,1* poles
were used in both the city and its suburbs. The poles
were then divided into several tens of clusters in
such a way that each cluster included at least one
crossing in it. Because the poles in one cluster line up
at least two roads intersecting each other, both nor-
th-south (NS) and east-west (EW) average strains
were obtained cluster-wise. Figs. 2 (a) and 2 (b) show
the distribution of remaining average strains in the
city. Contour lines in Figs. 2 (a) and (b) show inferred
layer boundaries of shear wave velocities Vs+// m/
s and Vs3** m/s, respectively (see Fig. -), and col-
ored zones show percentages of damage to dwellings
mapped by the National Cartographic Center of Iran
(,**.). In general, strains are large along the main
avenue that runs through the city from north to
south. Damage was also severe along this avenue
Fig. /. Transfer functions for pole P-+.
Strain Induced in Cracked Utility Poles and Damage to Dwellings from the Dec ,0, ,**-, Bam Earthquake
 63 
Fig. 0. Transfer functions for pole P-,.
Fig. 1. Comparison of P-+ spectra in three directions.
K. Konagai M. Yoshimi K. Meguro M. Yoshimura P. Mayorca M. Takashima A. Farahani H. Tahghighi M. Keshavarz
 64 
(Fig. 3 a), and it faded quickly as we got some street
blocks away from the avenue (Fig. 3b). Some severe
damage to dwellings was also found along Road #,,
which used to be an old river trace, and goes through
the city from East to West (Fig. 3 c). The strain
distribution thus seems to be consistent with the
overall damage distribution pattern. However, cali-
bration is necessary to interpret the strain distribu-
tion pattern in terms of intensity, in spite of the fact
that only one strong ground motion record was
available in the city (see the location on the map Fig.
2). A further discussion will appear in a future pub-
lication.
Fig. 2 b Strains remaining in poles : (Damage ratio provided by NCC of Iran, ,**.).
Strain Induced in Cracked Utility Poles and Damage to Dwellings from the Dec ,0, ,**-, Bam Earthquake
 65 
.. Summary
In countries such as Japan and Iran, which are
ranked among the most seismic hazard prone zones
in the world, strong ground motion networks are
often very dense for describing the seismological
features of earthquakes, but are very sparse for de-
scribing damage distribution, frustrating many at-
tempts to learn lessons from tragedies. Measuring
traces of strong ground motions remaining in struc-
tures, which are seen everywhere and have common
features, provides useful information for discussing
the spatial distribution of damage. RC utility poles
were taken as the target structures in Bam, the city
ﬂattened in the December ,0, ,**- earthquake. A
total of ,1* poles were used both in the city and its
suburbs. Clusters of poles with relatively large
strains were found mostly along (+) the main avenue
that runs through the city from north to south and
(,) along Road #,, which used to be an old river trace,
and goes through the city from East to West (Fig. 3
c). Dwellings along these roads were the most seri-
ously damaged. In general, the distribution of
cracked poles seems to have a good correlation with
damage distribution, which again showed the high
seismic vulnerability of adobe and unreinforced ma-
sonry structures.
Although it is possible to ban the use of adobe as
a construction material, which was actually done by
the Iranian Government, this measure is inapplica-
ble, as many people with limited resources will con-
(a) Near the main avenue.
N,3*1**./ E/2,+.+./ 11.
(b) East of the city.
N,3*0,-.- E/2,,-0.1 22.
(c) Along the Street #,
N,3*0,..0 E/2,++-.+ 1..
Fig. 3. Damage to dwellings in Bam.
K. Konagai M. Yoshimi K. Meguro M. Yoshimura P. Mayorca M. Takashima A. Farahani H. Tahghighi M. Keshavarz
 66 
tinue to use it. With this situation as a background,
it is necessary to provide fragility curves of adobe
structures to inform people of the possible scenarios
of serious destruction, and to improve the seismic
performance of their dwellings by retroﬁtting them.
Unfortunately, the poles do not directly show any
seismic intensity measures, just strains, although the
strain distribution obtained was apparently consis-
tent with the overall distribution of damage to dwell-
ings. Calibration is necessary, and this will be dis-
cussed in a future publication.
Acknowledgement
The authors would like to express their sincere
sympathy to the people a#ected by the killer earth-
quake. They are also grateful to all JAEE/JSCE
reconnaissance team members and collaborators
from Iranian organizations including the Interna-
tional Institute of Earthquake Engineering and Seis-
mology (IIEES) as the key counterpart, Building and
Housing Research Center (BHRC) and the University
of Tehran. The initiative taken by Prof. Mohsen
Ghafory-Ashtiany, President of IIEES, for organizing
the joint reconnaissance team is highly appreciated.
Prof. G. Heidarinejad, President of Building and
Housing Research Center, kindly provided the team
with necessary materials including digital data of
strong ground motions from the Bam earthquake.
Prof. R Alaghebandian and Prof. A. Ghalandarzadeh,
University of Tehran, joined the reconnaissance and
helped the team members providing geotechnical
and architectural pieces of information. The authors
wish to further collaborate with Iranian specialists
on possible countermeasures, e.g., reconstruction of
damaged structures, retroﬁtting of existing struc-
tures, and reducing earthquake hazards.
References
NASA: Destructive earthquake near Bam, ,**., http ://
www.parstimes.com/spaceimages/bam_ landsat.html
(Photo, taken on October +, +333)
National Cartographic Center of Iran, Damage distribution
to dwellings, Bam, ,**., http ://www.ncc.org.ir/bam/
BAMﬁnal_H_e.jpg
Walker, R., J. and Baker, C., ,**-, Surface Expression of
Thrust Faulting in Eastern Iran : Source Parameters
and Surface Deformation of the +312 Tabas and +302
Ferdows Earthquake Sequences, Geophysical Journal
International, +/,, 1.310/.
(Received February +1, ,**/)
(Accepted February ,+, ,**/)
Strain Induced in Cracked Utility Poles and Damage to Dwellings from the Dec ,0, ,**-, Bam Earthquake
 67 


2003年12月26日バム地震によって亀裂電柱に残留したひずみと家屋被害

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2003年12月26日バム地震によって亀裂電柱に残留したひずみと家屋被害

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