ORI GIN AL PA PER

The 27 August 2010 Mw 5.7 Kuh-Zar earthquake (Iran):field investigation and strong-motion evidence

Mohammad P. Shahvar • Mehdi Zare

Received: 19 April 2012 / Accepted: 20 November 2012 / Published online: 11 December 2012� Springer Science+Business Media Dordrecht 2012

Abstract In this study, seismological aspects and field observation of the 2010 Kuh-Zar

earthquake has been investigated. The Kuh-Zar earthquake, of magnitude 5.7 (Mw),

occurred in northeastern Iran on August 27, 2010. The area is surrounded by branches of

the active faults which are coated by the quaternary alluvium. During the past several

decades, this area has been struck by a number of earthquakes. This earthquake with a

moderate magnitude caused a higher rate of damage contrasted with previous earthquakes

of the same magnitude range in Iran. Fortunately, the source of the Kuh-Zar earthquake

was in a sparsely populated area, and therefore, it caused a few loss of life with the highest

observed intensity of shaking VII (modified Mercalli intensity) in the Kuh-Zar village. The

shock killed 4 people, injured 40, and destroyed more than 12 villages. According to the

field observation, the mechanism of this shock is defined as a left-lateral strike slip. We

also checked out the properties of strong ground motions in this earthquake using the

records availed by Iranian strong motion network. At KUZ station, about 7 km east of the

epicenter, the recorded PGA and PGV in both horizontal and vertical components were

remarkably large for an event of this size, and visual inspection of the velocity time history

reveals a pulse-like shape. Unfortunately no other recording stations were located close

enough to the fault to capture a directivity pulse. Finally, according to the strong-motion

properties and observed information, ShakeMaps of the earthquake have been generated by

the native intensity observations and the recorded strong motions.

Keywords Macroseismic intensity � Instrumental ShakeMaps � Kuh-Zar � Strong motion �Velocity pulse-like shape

1 Introduction

The effort in this study is to represent the macroseismic damage, strong-motion prop-

erties, and the post-earthquake observations focusing on determination of modified

M. P. Shahvar � M. Zare (&)International Institute of Earthquake Engineering and Seismology, Tehran, Irane-mail: mzare@iiees.ac.ir

123

Nat Hazards (2013) 66:689–706DOI 10.1007/s11069-012-0507-8

Mercalli intensity in the Kuh-Zar earthquake of August 27, 2010. The Kuh-Zar earth-

quake of August 27, 2010, with a magnitude of Mw 5.7 (GCMT), ML 6 (IIEES), and MN

5.9 (IRSC) occurred in the Kuh-Zar region, a sparsely populated desert region of the town

of Damghan, north-central Iran, close to the border of the southern Alborz region (see

Fig. 1).

Despite the low population density and moderate magnitude, the earthquake killed 4

people (two children and two women), injured 40, destroyed 50 houses, left a further 800

homeless, and damaged 300 more houses in nearby villages including Kuh-Zar, Salmabad,

Tuchahi, Kelu, Shemi, Bidestan, Hoseynian, Moalleman, Satveh, Reshm, Mehdiabad, and

Torud, which are located in the Semnan province in north-central Iran.

The goal of present study was mapping the correlation between instrumental intensity

and observed macroseismic effects of the Kuh-Zar earthquake. In this article, after

describing the tectonic features and structural trends in the macroseismic region, we will

present the field observation study, methodologies, and finally the results.

Fig. 1 Instrumentally recorded earthquakes in the north-central Iran region in the period 1939–2010(circles), using the catalog of ISC, IRSC, and IIEES, and Engdahl et al. (2006). The diamonds show theepicenters of historical earthquakes reported by Ambraseys and Melville (1982). The star indicates theepicenter of the last major event in the north-central Iran region. The beach ball indicates the left-lateralfocal mechanism of the 2010 Kuh-Zar earthquake

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2 Area of study

2.1 Geology and tectonics of the area

The Iranian Plateau has been frequently affected by disastrous earthquakes resulting in

massive loss of life (Berberian 2005). The Iranian Plateau can be characterized by active

faulting and folding, varying crustal depths, and mountainous topography. For the basic

geology of Iran as a whole, the country can be separated into four main parts on the basis of

regional differences in tectonic-sedimentary characteristics and metamorphism: 1-the

Zagros region; 2-Central Iran; 3-the Alborz Mountains; and 4-Kopet Dagh (Nabavi 1971;

Berberian 1976). The area represented in this study is located in north-central Iran (the

middle northern part of central Iran), close to the boundary of the southern Alborz

Mountains. The fundamental contributions to studies of active faulting in Iran were pre-

pared by Tchalenko and Ambraseys (1970), Tchalenko et al. (1974), Tchalenko (1975),

Tchalenko and Berberian (1975), Berberian (1976, 1981), and some others. The latest

compilation of available data about active faulting is from Hessami and Jamali (1996).

This area is surrounded by branches of the active Damghan and Shahvar fault system in

the north. The motion of this fault system is left lateral (Wellman 1966). The fault system

comprises a series of branches extending from north of Tehran to northeast of the city of

Shahrud (Fig. 1). The area leads to the Dorune fault in the south, which is approximately

600 km long and contains several indications of cumulative left-lateral slip over various

scales (Fattahi et al. 2007). During the past several decades, a number of earthquakes

(Table 1) have occurred within this area with magnitudes of 3.2 to 6.6 (Ambraseys and

Moinfar 1977). Both faults located around the epicenter are capable faults, and several

other branches of the Torud fault system and other faults are within this area.

The Torud fault was considered the causative fault for the 1953 Torud earthquake

(Berberian 1977). The only geological evidence of the neotectonic activity of the Torud

region is its seismicity, which is assumed to be related to the Torud seismogenic fault

Table 1 August 10, Pre-2010 (Mw 5.7 Kuh-Zar earthquake) seismicity of moderate-sized earthquakes

Date(mm/dd/yyyy)

Lat (�) Lon (�) Magnitude(Mw)

Reference

6/26/1808 35.3 54.5 6.6 Ambraseys and Melville (1982)

7/22/1927 34.9 52.9 6.3 Ambraseys and Melville (1982)

4/6/1939 35.5 54.5 5.6 GUTE

2/12/1953 35.6 54.7 6.5 Ambraseys and Melville (1982)

2/13/1953 35.6 54.7 4.5 Ambraseys and Melville (1982)

4/1/1953 35.5 55.2 4 Ambraseys and Melville (1982)

7/11/1953 35.9 55.1 4.3 Ambraseys and Melville (1982)

7/24/1953 35.8 55.4 4.5 Ambraseys and Melville (1982)

8/24/1953 35.4 54.8 4.7 Ambraseys and Melville (1982)

2/16/1990 35.946 54.471 5 ISC

2/16/1990 35.905 54.559 4.6 EHB

7/3/2000 35.943 54.79 3.8 ISC

9/2/2004 35.622 54.385 4.1 ISC

10/23/2005 35.885 54.457 3.2 ISC

27/8/2010 35.457 54.5497 5.7 GCMT

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(Khademi 2008). The metamorphic rocks of the Torud complex are composed of gneiss,

schist, marble and amphibolites. These rocks extend approximately 115 km, with a

northeast-southwest trend from Torud to south of Abassabad and the surrounding areas of

the fault including the Torud, Reshm, Hoseynan, Bidestan, Moalleman, Kuh-Zar and

Mehdiabad villages. The metamorphics of the Torud had previously been considered

Precambrian and pre-Devonian in age, but are now assigned to the post-Jurassic/pre-

Cretaceous (Hushmandzadeh et al. 1973). This fault is coated by the Quaternary alluvium

for most of its length (Khademi 2008).

2.2 Seismicity of the region

The long-term seismicity of the Iranian plateau has been studied by Ambraseys and

Melville (1982), Berberian (1981, 1995a, b, 1996, 2005), and Berberian and Yeats (1999,

2001).

A map of earthquake occurrences, which contains instrumentally recorded and historical

earthquakes, is shown in Fig. 1. Also, the macroseismic areas of the major events and their

associated ruptures are displayed in Fig. 2. The last significant earthquake reported in the

Torud area was on February 12, 1953 (Fig. 2). Torud village was completely demolished

by this earthquake, though a few houses did not collapse (Abdalian 1953; Ambraseys and

Moinfar 1977). The earthquake was associated with NE-SW surface faulting with a total

displacement greater than 1.4 m for a surface trace greater than 8 km, and the Ms was 6.5

(Ambraseys and Jackson 1998). At the time of the 1953 earthquake, Torud had a popu-

lation of approximately 2,100, and the reported casualties were approximately 920 (Ber-

berian 1977). Another destructive event, according to Gansser (1969), was the June 26,

1808, Reshm earthquake, which had a magnitude of Ms 6.6 (Ambraseys and Melville

1982). This earthquake completely devastated the area of Reshm village.

Fig. 2 Map showing epicenter of the aftershocks (circles) corresponding to the 2010 Kuh-Zar earthquake.The regions of previous significant earthquakes are surrounded by dashed lines. The active faults are markedby solid lines and the villages are pointed by squares

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Another major shock in this area was the earthquake of July 22, 1927, of magnitude 6.3,

(Nowroozi 1976; Ambraseys 1978), which caused minor damage in Satveh village. The

epicenter of this event was approximately 150 km west of Torud; nonetheless, it was

strongly felt there. There was again some minor damage in Satveh and rock-falls near

Reshm caused by the earthquake of April 6, 1939 (Ambraseys and Moinfar 1977). All

major earthquakes that have occurred are listed in Table 1. The lack of more extensive

historical records is due to the region being sparsely populated and located in the distant

desert surroundings north of Dasht-e-Kavir Desert in north-central Iran.

3 The 2010 August 27 Kuh-Zar earthquake

At 19:23 UTC (11:53 local time), August 27, 2010, an Mw 5.7 earthquake struck the Kuh-

Zar and Torud region in north-central Iran. The earthquake exhibited an almost pure strike

slip on the NE–SW striking fault plane, with a dip of approximately 78� (Table 2, Fig. 1).

The focal mechanism for this earthquake is available from the Global CMT catalog

(Table 2). The main shock was followed by several small-magnitude aftershocks, although

a large one occurred at 00:29 UTC (mb 5, Fig. 2).

4 Field observations

4.1 Coseismic surface ruptures

There was no significant surface faulting along the region of the 2010 August Kuh-Zar

earthquake, but there were some secondary cracks and fractures (Fig. 3a). The earthquake

produced fissuring along the Tuchahi village (Fig. 3b, c), following the eastern part of this

area. Some cracks were found in Kelu village that were similar to previously found effects

(The villages is shown in Fig. 3).

4.2 Damage to buildings

More than 80 % of the rural houses in Iran are composed of adobe or stone masonry and

are constructed using only local materials and unskilled labor (Maheri et al. 2005). In the

Kuh-Zar region, the greatest intensity of damage was due to the traditional construction,

very poor clay materials, single-story houses of weak masonry, non-reinforced adobe

(Fig. 3d), overloaded construction, and flat wooden and steel-beamed roofs (Fig. 3e), a

number of which were damaged in the earthquake. Moreover, several non-reinforced free-

standing brick or clay walls around houses and gardens in the Tuchahi and Kelu villages

also fell. The majority of these houses in the epicentral region underwent partial collapse,

in numerous cases causing progressive failure, typically starting at the wall corners and

moving forward into the walls, making the roof collapse in the same way as most previous

Table 2 Fault parameter from the Global CMT

Fault plan Strike (�) Dip (�) Slip (�) Centroid depth (km) Magnitude (Mw)

1 212 78 -2 14 5.7

2 302 88 -168

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devastating earthquakes (Fig. 3f). Figure 3f shows the place where two women were killed

due to a partial roof collapse. Water and power supplies in the epicentral area were also

severely disrupted and not restored until 36 h after the earthquake. In addition, some cases

of changes in groundwater levels were reported in Kelu village.

Fig. 3 Field photographs: a Coseismic fracture near the epicenter (Foroutan et al. 2010). b Crack from the2010 Kuh-Zar earthquake (near the epicenter), cracks strike E to W. c Fissuring in Kelu village, 5 km fromthe epicenter, crack strike is N70. d Typical adobe-brick house at Kelu; the non-load-bearing walls collapsein an earthquake first. e Collapse started in the corner, where it was easier to initiate instability. f Collapse ofmasonry arches due to the movement of the roof with unanchored slab, poor connection composite, andweak slab materials. g Partial damage of the reinforced concrete elementary school building at Kuh-Zar,4 km E of the epicenter. This structure was built 4 months before the Kuh-Zar earthquake of 2010 August27 (Mw 5.7)

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Fortunately, no infrastructures such as bridges, tunnels, dams or power plants were in

proximity. The only engineering structure close to the epicentral region was a newly

constructed school. This school had been inaugurated a few months before the earthquake

and was partly damaged during the earthquake (Fig. 3g).

5 Methodologies

5.1 Strong-motion processing

The strong-motion records are accessible only in an uncorrected format; therefore, as a first

attempt, they must be corrected for baseline shifts, high-frequency noise, and long-period

impacts. The strong-motion data of all of these stations were processed following the

method introduced by Boore et al. (2002) and Boore and Bommer (2005). The velocity and

displacement time histories of the records were obtained based on single and double

integration of the accelerograms.

By correcting the records, to assess the characteristics of the near-fault strong motion

from the earthquake, the horizontal records were rotated in strike-parallel and strike-

normal directions. Then, we used the pulse classification algorithm proposed by Baker

(2007) because it is an entirely quantitative technique that allows classification of the large

dataset of the next generation attenuation (NGA) database (Chiou et al. 2008). The seismic

action is evaluated using the previously mentioned approach comparing velocity pulses

and non-pulse-like signals. This approach uses wavelet analysis to extract the largest

velocity pulse from the velocity time history of the ground motion (Baker 2007). The pulse

indicator relation (Eq. 1), which is suggested in Baker (2007), takes values between 0 and

1. Records with values above 0.85 and below 0.15 are classified as pulses and non-pulses,

respectively.

PI ¼ 1

1þ e�23:3þ14:6 PGVrð Þþ20:5ðErÞð1Þ

where PI is the pulse indicator value (unit less), PGVr (PGV ratio) is the peak ground

velocity of the residual record divided by the original record’s PGV, and Er (energy ratio)

is the energy of the residual record divided by the original record’s energy. The outcome of

this approach can be compared with their respective particle motions to confirm the

presence of velocity pulse-like shape.

As a final step, we produced the ShakeMaps (Wald et al. 1999) of the 2010 Kuh-Zar.

The production of estimated maps of shaking after an earthquake, such as ShakeMap offers

an important seismological tool to guide emergency response and loss estimation for public

information through emergency response networks, the Internet, and the media.

ShakeMaps are fundamentally obtained from the recorded ground motion parameters

(PGA and PGV). If no records are available, they could be derived by ground motion

predictive equations.

5.2 Intensity measurement

Different intensity scales have been employed in Iran at various times. The first isoseismal

map in Iran was made by Abdalian (1953) for the Torud earthquake of February 12, 1953

(Berberian 1976) based on modified Mercalli intensity (Wood and Neumann 1931). In the

present study, the modified Mercalli intensity scale has been used to describe the power of

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earthquake, at a given locations, based on actual observation of natural features, human

being, damaged structures, and presence of secondary effects.

6 Results

6.1 Strong-motion parameters

The Building and Housing Research Center (BHRC) of the Ministry of Housing and Urban

Development solely operates the Iranian Strong Motions Network (ISMN). The strong

motions of this event were recorded at 7 stations of the ISMN (According to the BHRC

2010 report). All of the strong-motion data obtained during the Kuh-Zar earthquake were

recorded by digital Kinemetrics SSA-2 accelerographs. The strong-motion stations are not

uniformly distributed in the area, as shown in Fig. 4, but are mostly located at the north

side of the earthquake epicenter due to the vast desert that is located to the south. The

velocity and displacement time histories of the Kuh-Zar records, which were obtained

based on single and double integration of the accelerogram, are shown in Fig. 5.

Three stations (KUZ, TRD, and MLM) are in relatively close proximity to the Kuh-Zar

mainshock source, but only KUZ recorded the event. Of all 7 triggered stations, only one

was located close to the event (Fig. 4). The record obtained at KUZ (Fig. 5) after the

exertion of band-pass filtering shows a vertical ground acceleration (PGA) of nearly

369 cm/s/s and a horizontal acceleration of 550 and 501 cm/s/s for the strike-parallel and

strike-normal components, respectively. Information regarding the locations of stations,

Fig. 4 Strong-motion stations surrounding the epicentral region. The seven activated stations are shown bythe larger triangle within a 1–126 km range of the rupture registered in the earthquake with a peakacceleration of nearly 0.55–0.08 g, respectively. The deactivated stations are shown by the small triangles.The recorded motions of activated stations plotted in front of the stations

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component orientations, site conditions, distance, PGA, PGV, and PGD is summarized in

Table 3.

The pulse classification algorithm results related to KUZ are shown in Fig. 6a, b and

Table 4. According to Table 4, the pulse indicator (Eq. 1) for the strike-parallel ground

motion is predicted as 0.98. This motion meets all three criteria described in Baker (2007):

(1) The pulse indicator value (Eq. 1) is greater than 0.85. (2) The pulse arrives early in the

time history. (3) The original ground motion has a PGV of greater than 30 cm/sec.

One of the important parameters for structural engineers is the period of the velocity

pulse, as the ratio of the pulse period to the fundamental period of the structure can

significantly affect the structure’s response (Alavi and Krawinkler 2001; Mavroeidis et al.

2004). The pulse period for this earthquake is identified as approximately 1.51 s. Ground

motions with a pulse at the beginning of the velocity time history cause severe damage to

structures. Despite these velocity pulses, the structural damage around the instrument was

not devastating. Initially, this was interpreted by the period of the pulse being much larger

than the fundamental periods of the structures nearby (0.1 s).

In addition, Fig. 7 demonstrates the particle motions of acceleration, velocity, and

displacement of the KUZ station records on three orthogonal planes after rotation into

fault-oriented coordinates, using a fault strike of N212 as the reference fault parallel. Only

Fig. 5 Corrected acceleration, velocity, and displacement time histories of the strike-parallel, strike-normal, and up-down components of strong motion recorded at the KUZ station during the 2010 Kuh-Zarearthquake

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698 Nat Hazards (2013) 66:689–706

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the first 5 s of the record was used to include the time duration until the rupture passes near

the station. Figure 7 showing the velocity pulse orientated largely in the fault-parallel

direction. Note that the azimuth of P wave is nearly along the station-azimuth line.

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Fig. 6 The decomposition procedure diagram of the 2010 Kuh-Zar earthquake, recorded at KUZ. From topto bottom: original recorded velocity, extracted pulses, and residual signals. a Strike-parallel component.b Strike-normal components

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6.2 Uncertainty in the location

The European-Mediterranean Seismological Centre (EMSC) relocated this event by

gathering all available phase arrival data from permanent seismic stations in Iran and

worldwide (Using 525 stations, rms = 1.38 s). The confidence-ellipse of the Kuh-Zar

epicenter has semi-major axis 4.8 km and semi-minor axis 2.6 km at the confidence level

Table 4 Results of pulse identification for horizontal components of Kuh-Zar strong motions recorded

Component Pulse indicator Tp (sec) PGV (cm/s) Late pulse indicator Classified as pulse

Strike parallel 0.98 1.51 46.78 0 1

Strike normal 0.01 0.26 12.63 1 0

The component which is classified as a pulse shown by bold

Fig. 7 Acceleration, velocity, and displacement particle motions calculated from the recorded accelerationsof the Kuh-Zar station (KUZ) on three planes. The effects of source rupture are shown by the considerableamplitude in the strike-parallel direction at velocity and displacement

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of 95 %. The EMSC location analysis gives as epicenter coordinates 35.49N and 54.55E

with a depth of 10 km. Although the estimated epicenter is reasonable constrained, the

accuracy of depth is uncertain due to the lack of nearby station.

Hence we used S–P phase readings from the closely spaced accelerometer station

(KUZ) to estimate the limitation of likely source depth. Based on S wave and P wave

velocities of 3.36 and 5.8 km/sec, with differential times calculated from our picks of S

and P arrivals (1.64 s), the hypocenter distance of this earthquake was estimated to be

13 km which confirms that the event was shallow. Finally, given the EMSC epicenter, a

depth of 11 km is calculated which is consistent with the depth determined by the EMSC.

6.3 Macroseismic intensity map

In Fig. 8 the intensity map is shown for Kuh-Zar region and the surrounding areas, which

was determined through interviews and field observations. The 2010 earthquake destroyed

the Kuh-Zar, Salmabad, Tuchahi, Kelu, Shemi, Bidestan, Hoseynian, Moalleman, Satveh,

Reshm, Mehdiabad, and Toroud villages.

The 2010 Kuh-Zar earthquake killed 4, injured 40, left 800 homeless, and damaged

seven villages [Salmabad (MMI intensity VII), Tuchahi (VII), Kelu (VII), Shimi (VII),

Kuh-Zar (VII), Bidestan (VI), Hoseynian (VI), Moalleman (VI), Satveh (VI), Reshm (VI),

Mehdiabad (VI), and Torud (VI) (Fig. 8)]. The closest strong-motion instrument that

recorded the main shock was KUZ station (7 km east of epicenter, see Fig. 4), which

recorded a 0.550 g acceleration on the horizontal component (Fig. 4). Moreover, the shock

Fig. 8 Isoseismal map of the earthquake area showing the main tectonic and damage features. The intensitygrades correspond to the modified Mercalli Scale and the main observed sites are shown by squares

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was felt strongly in Forat (V on MMI, 55 km north of Kuh-Zar), Damghan (IV?, 80 km N)

and Shahrud (IV, 110 km NE) and less strongly in Seman (III?, 105 km NW), and Tehran

(II, 270 km NW).

6.4 ShakeMaps of the Kuh-Zar 2010 earthquake

Figure 9a shows a ShakeMap based on magnitude, epicenter, and finite fault representa-

tion. The data used to produce the ShakeMap are collected by seven strong-motion records

around the epicenter and are improved with macroseismic intensity data of 53 places based

on the observed effects of ground shaking on people and buildings. The area of variant

intensities is divided using the collection of each contour. The annotation number of

contour levels corresponds to a modified Mercalli scale. The PGA and PGV ShakeMaps

generated by IIEES are shown in Fig. 9b, c.

For easy evaluation of the uncertainty of a ShakeMap, a color-coding map was intro-

duced by Wald et al. (2008) and Worden et al. (2010). The average value and the corre-

sponding letter grade on the scale on the right side is displayed on the bottom left of the

uncertainty map (Fig. 9d). Also, the area of intensity of VI or higher, over which the

average uncertainty is computed, is shown with a bold black line. The derived ShakeMaps

(Fig. 9a, d) indicate that the instrumental intensity is in strict conformity with macrose-

ismic intensity.

7 Conclusions

This study has investigated the 2010 Kuh-Zar earthquake using seismological aspects,

geomorphology, structural damage from field observations, and the study and process of

strong-motion instrumental records of stations near the earthquake source. The results of

the field investigation together with the strong-motion evidence are presented herein to

provide a seismological view of the event.

The Kuh-Zar earthquake, of magnitude 5.7 (Mw), occurred in northeastern Iran on

August 27, 2010, not far from the region where the 1953 earthquake caused considerable

damage and devastation. Although the earthquake was not of a severe size, the damage

level was high. This level of damage can be associated with the shallow depth of the

earthquake, non-engineered construction, brittle building materials, weak element con-

nections, and excessive weight. The shock was felt within a radius of 280 km, and it killed

4 people, injured 40, and destroyed more than 12 villages. Furthermore, the shock damaged

more than 300 houses. The highest intensity of shaking VII (MMI) was observed in the

Kuh-Zar village. The earthquake was not associated with any significant surface faulting,

but with coseismic folding.

The source of this shock was reported to have had a left-lateral strike-slip mechanism

initiated in a fault in the northeastern-southwestern direction. A regional strong-motion

Fig. 9 ShakeMap for the Kuh-Zar 2010 earthquake. In these figures, the small filled dots show the observedsites and the triangles show the activated strong-motion stations during the earthquake. a The instrumentalintensity map generated by magnitude (Mw 5.7), finite fault, and using observed macroseismic intensity.The Arabic numbers correspond to the level of estimated intensity. b PGA ShakeMap for the Kuh-Zar 2010earthquake. The numbers show the estimated PGA for the region. c PGV ShakeMap for the Kuh-Zar 2010earthquake. d ShakeMap uncertainty map for the Kuh-Zar 2010 earthquake corresponding to the intensitymaps in Fig. 9b; the grade is ‘‘A’’ (Mean sigma 0.917). The dark places show the dominant contributionfrom the native intensity observations

c

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Fig. 9 continued

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network consisting of 7 strong-motion stations (SSA-2 Accelerograph) located within

1–126 km from the epicenter, recorded the earthquake. The pulse-shaped arrivals of strong

signals recorded at the Kuh-Zar station strongly suggest that velocity pulses can be

identified in fault-parallel components by the considerably larger amplitude. Despite this

velocity pulse, the structural damage around the instrument was not devastating. Initially,

this was interpreted by the period of the pulse being much larger than the fundamental

periods of the structures nearby.

Acknowledgments This study is based on the results obtained from a research project in the InternationalInstitute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran, directed by the second author ofthis article. We are grateful to Vahid Gholami and Majid Maybodian, PhD students of IIEES, for accom-panying us in the field. We would like to thank BHRC and Dr. Fereidoun Sinaeian for providing the strong-motion data. Most of the figures were produced using the GMT software of Wessel and Smith (1998). Alsowe are thankful to two anonymous reviewers of this article for their ideas and comments. With implyingtheirs comments and suggestions, we believe that the quality of the article has been upgraded.

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