Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanTHE CHARACTERISTICS OF SEISMIC, STRONG
MOTION AND STRUCTURAL DAMAGE OF THE 2011
VAN-ERCİŞ EARTHQUAKE
Kazuo KONAGAI1, Reşat ULUSAY2, Halil KUMSAR3, Ömer AYDAN4 and MehmetÇELEBİ5
1

Professor, Institute of Industrial Science, University of Tokyo,
Tokyo, Japan, konagai@iis.u-tokyo.ac.jp
2
Professor, Department of Geological Engineering, Hacettepe University,
Ankara, Turkey, resat@hacettepe.edu.tr
3
Professor, Department of Geological Engineering, Pamukkale University,
Denizli, hkumsar@pamukkale.edu.tr
4
Professor, Ocean Research Institute, Tokai University,
Shizuoka, Japan, aydan@scc.u-tokai.ac.jp
5Senior Research Civil Engineer, USGS,
Menlo Park, USA, celebi@usgs.gov

ABSTRACT: An earthquake with a moment magnitude (Mw) of 7.1 and a local
magnitude of 6.7 occurred at 13:41 local time on October 23, 2011 in the Van province ofeastern Turkey, which is known to experience large earthquakes in the past. As previous
earthquakes did, this earthquake also caused heavy damages to buildings and otherstructures particularly in the town of Erciş. Collapse of numerous residential andcommercial buildings resulted in 604 fatalities and 2608 injuries during the main shock.
Following a brief outline of geology, seismo-tectonics and geotechnical conditions in the
town of Erciş, an evaluation of strong ground motion characteristics and structural
damage are described and the findings and lessons learned from this earthquake arepresented.
Key Words: Van-Erciş earthquake, geology, thrust faulting, high ground motions,directivity effect, structural damage

INTRODUCTION

An earthquake with a moment magnitude (Mw) of 7.1 occurred at 13:41 local time on October 23,2011
in the Van province of Turkey (USGS (2011).). The major energy release occurred within 20 seconds
although the total duration of the rupture was about 50 seconds. Kandilli Observatory and Earthquake
Research Institute (KOERI) estimated that the epicenter of the earthquake was near Tabanlı village(38.628N, 43.486E). The earthquake originated at a depth of 20 km and it was resulted from the
movement of a 50 km long and 20 km wide thrust fault trending about E-W direction from Erçek Lake

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into Van Lake.
The earthquake was felt over a large area in the eastern and southeastern parts of Turkey,
particularly in the province of Van, which had a total population of 1,035,418 as of 2010 (The City of
Van and the town of Erciş had populations of 539,619 and 145,229, respectively). The earthquake
resulted in heavy damage to buildings and significant casualties in this province, particularly in the
town of Erciş, the City of Van and a number of villages in the province. The number of fatalities is 604
and the number of injured people is 2608, both caused by collapsed or damaged residential andcommercial buildings.
In the first part of the paper, a brief outline of geology, seismo-tectonics and geotechnicalconditions of the town of Erciş and its close vicinity is given. The second part involves seismic
characteristics of the earthquake and evaluation of strong ground motion characteristics. The third partdescribes structural damages. In the final part, the findings and lessons learned from this earthquake
are presented.
GEOLOGICAL AND GEOTECHNICAL CONDITIONSThe Van Lake Basin is located in the East Anatolian Plateau, which has resulted from the collision
between the Eurasian an Arabian Plates in Late Miocene (Şengör and Kidd, 1979; Şengör and Yılmaz,
1983). The basin, formed in Late Pliocene (Şaroğlu and Yılmaz, 1986), is underlined by a basement
consisting of Bitlis Metamorphics, Upper Cretaceous ophiolites and Tertiary aged marine sediments.
In the region surrounding Van Lake, different rock units and alluvial deposits formed between
Paleozoic and Holocene are observed. As seen from the simplified geological map given in Fig. 1, theVan Lake region includes metamorphic rocks belonging to the Bitlis Massive at the south, volcanicand volcano-clastic rocks at the west and north originated from the old volcanoes called Nemrut
Süphan and Tendürek.

Fig. 1 Simplified geological map of the close vicinity of Van Lake (modified from Üner et al., 2010)
The Van formation, outcropping at the south of Van, west of Erciş and Adilcevaz towns at the north,mainly consists of alternations of loosely packaged sandstone, mudstone and turbitides including
pebble layers. This formation has thinly-to-moderately spaced beddings. The majority of these
deposits have formed depending on the variations in the water level of Van Lake occurred after the1903latest ice period and they unconformably overlie the old units (Altunkaynak et al., 2003).
The Holocene deposits in the region consist mainly of alluvial fan deposits, lacustrine andfluviatile deposits and debris material including loosely-to-moderately cemented gravel, sand, silt andunconsolidated clay horizons. Selçuk and Çiftçi (2007) interpreted these sediments as representing
four phases of deposition, such as lacustrine deposits, lacustrine-fluviatile deposits, shore sanddeposits and recent fluviatile deposits
Van Lake, situated at 1,648 m above sea level in the eastern Taurus Mountains of southeast Turkey
is the fourth largest terminal lake in the World (a body of water with streams discharging into without
any out-flow). Its surface area is about 3,600 km2 and mean depth is between 200 and 300 m withmaximum water depth measured as 451 m near Adilcevaz at north. The lake water elevation varies
between 1648 and 1650 m since 1969 and an increase of 2 m in water level was observed between
1987 and 1997, and then a drop in water level occurred until 2001 (Landmann and Reimer, 1998). In
this area, there are ten big rivers flowing into the lake following different paths. Among them, theKarasu River, flowing in NE-SW direction, is the longest river in the earthquake affected area andforms a large plain at the north of Van.
Similarly, Zilan Stream creates another plain in the vicinity of Erciş at the northern part of Van
Lake (Fig. 2). As the damage was quite heavy and extensive in Erciş due to the October 23, 2011
earthquake, a brief outline of hydro-geological and geotechnical conditions of Erciş region is
discussed herein.
Zilan and İrşat streams form the main drainage system of the Erciş Plain. The aquifer in this area
consists of Plio-Quaternary deposits with a thickness reaching up to 188 m (DSİ, 1977). The
measurements from 11 water wells indicated that depth of the static water level was between 0 and 12
m, and in some boreholes artesian pressures were also noted. Özvan et al. (2008) indicated shallow
depths of groundwater table ranging between 1 and 8 m in their geotechnical investigations in Erciş
town. The direction of groundwater flow is towards SE and SW and the depth of groundwater tablebecomes considerably shallower near to the lake (Fig. 2).

Fig. 2. Geology and hydrogeology of Erciş Plain (re-arranged from Özvan et al., 2008)

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TECTONICS, FAULTING MECHANISM AND AFTERSHOCK ACTIVITY
Keskin (2003) proposed a general tectonic model for Eastern Anatolia to explain the uplift of the crustand main driving forces of crustal deformation and associated earthquakes. The tectonics of the region
is influenced by the northward moving and subducting Arabian plate beneath the Anadolu plate. The
Anadolu plate squeezed between the Arabian plate in the south and Euro-Asian plate in the north. As aresult of these crustal movements, there are EW trending thrust faults and major fold axis and NW-SE
and NE-SW trending strike-slip faults. Şaroğlu and Yılmaz (1986) studied the neotectonics of theEastern Anadolu in a broad sense and recognized some major folding axes in the epicentral area andsome faults in the north and north-east of Van Lake.
The major active faults of the region are shown in Fig. 1. Regarding the active fault map ofTurkey prepared by Maden Tetkik Arama (MTA, 1992), it is interesting to note that no active fault isrecognized in the epicentral area. Ketin (1977) was first person studying the tectonics of the epicentral
region following the 1976 Çaldıran earthquake. He pointed out the possible traces of faults, which areactivated during this earthquake and indicated the necessity for further investigations. Besides themain thrust faults trending E-W, there are conjugate strike-slip faults with some normal components.
Özkaymak et al. (2004) recognized thrust and NW-SE and NE-SW trending strike-slip faults. One ofthem is a thrust fault observed near the campus area of Yüzüncü Yıl University (YYU) located at the
NW of the Van city center. This fault is a reverse fault trending N70E and dipping 45NW. It isobserved to cut across the recent lacustrine deposits of Van Lake. The fault offset changes from about
90 cm in the older deposits to about 20 cm in the youngest sediments just below the soil horizon,suggesting that the fault surface was reactivated several times. A more detailed tectonic map of theepicentral area has been released by Koçyiğit et al. (2011) following the earthquake as shown in Fig. 3.
He also attempted to relate the faults drawn in his map with the focal mechanism solutions of mainand major aftershocks. However, his attempt is quite disputable in many aspects.
The major earthquakes in the close vicinity of Van Lake are 1941 Erciş (Ms 5.9), 1966 Varto (Ms6.8), 1975 Lice (Ms 6.6) and 1976 Çaldıran (Ms 7.3) earthquakes. While Varto and Lice earthquakes
are of thrust type, Çaldıran (Ms 7.3) earthquake has a strike-slip character. The 1976 Çaldıran (Ms 7.3)
earthquake also induced some discussion on the continuity of North Anadolu Fault Zone (NAFZ) tothe east of Van Lake extending towards Iran. Two intermediate earthquakes having moment
magnitudes of 5.4 on 1988 June 14 and 5.7 on 2000 Nov. 15 recently occurred in the eastern part of
Van Lake. The faulting mechanism of these earthquakes were of thrust type.
Kandilli Observatory and Earthquake Research Institute (KOERI) estimated that the earthquake
was centered about 30 km north of the Van city center near Tabanlı village. The rupture mechanisms
released by different institutes (USGS, 2011; HARVARD, 2011; KOERI, 2011; ERD, 2011; GFZ,
2011) implied that the rupture was due to thrust type faulting together with an inference from fault
striation in Topraktaş village as shown in Fig. 3. If the seismicity shown in Figure 4 is considered, theNW dipping faults may be assumed to be the causative fault with a slight sinistral component. The
average inclination of the NW dipping fault may be about 40 degrees. Although the estimated averagerelative displacement of the fault is more than 2 m according to the empirical relation proposed by
Aydan (2007), there was no clear fault scarp on the ground surface (Photo 1). The earthquake
originated at a depth of ranging between 5-19 kilometers depending upon the institutes and it was
resulted from the movement of a 50 km long and 20 km wide thrust fault trending about E-W direction
from Erçek Lake into Van Lake. The major energy release occurred within 20 seconds although thetotal duration of the rupture was about 50 seconds.

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Fig. 3 Faults mapped by Koçyiğit et al. (2011) and focal mechanism solutions by various institutes

Fig. 4 Aftershock activity following the main shock (aftershock data from ERD)

1906

38.579067, 43.269401

38.578987, 43.270034

38.582694,43.300295

Photo 1 Views of surface rupture along the fault trace (base map from Emre et al., 2011)38.996624,43.398625

38.996632,43.402616

38.791523,43.291798

38.760375, 43.226309

38.560952,43.277893

Photo 2 Views of uplift of shoreline at several localities along Van Lake

1907

One of the typical effects of this earthquake is a change in the shoreline of Van Lake as seen in
Photo 2. Similar observations were also reported for Erçek Lake (ERD, 2011). The measurements at
certain locations on the lakeshore at the northern and eastern parts of the earthquake region by theauthors during reconnaissance indicated that uplift of the recent shoreline ranging between 15 and 35
cm has occurred.
CHARACTERISTICS OF STRONG MOTIONS
The distances from the earthquake epicenter to Van and Erciş were approximately the same. However,the damage was quite heavy in Erciş as it was on the hanging-wall side of the causative fault while thedamage in Van city was relatively less probably because it was on the footwall side of the causative
fault. Unfortunately, no strong motion was recorded in neither Van nor in Erciş although Van and Erciş
are equipped with strong motion devices. It seems that it did not record any strong motion data due toa technical malfunctioning.
The nearest strong motion station to the epicenter of the main shock was located in Muradiye(38.99011N-43.76302E) and the maximum ground acceleration at this station with a shear velocity of
293 m/s was about 0.2 g (ERD, 2011). The distance of Muradiye station to the epicenter is almost thesame as that of Erciş. Fig. 5 shows the acceleration records taken at Muradiye and Bitlis(38.46600N-42.15000E). The acceleration response of these strong motion stations together with thoseof Malazgirt and Muş strong motion stations are shown in Fig. 6. Maximum spectral acceleration are
observed for a natural period of 0.4 seconds for Muradiye record. In view of natural periods common
to reinforced concrete (RC) structures in Turkey, the acceleration response of 6 and 8 story RC
buildings should have been very higher. This result can explain why 6–8 story RC buildings collapsed
or heavily damaged during this earthquake. As for the acceleration of strong motion stations such asMuş, Malazgirt and Bitlis away from the epicenter, the effect of long period components appear as
expected. For example, the collapse of minarets in Muş and Malazgirt can be explained by long period
components for strong motion records.

Fig. 5 Acceleration records taken at Muradiye and Bitlis strong motion stations

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Fig. 6 Acceleration response spectra at selected strong motion stations
Fig. 7 compares estimations by several attenuation relations for maximum ground acceleration andmaximum ground velocity with observations. The observed data are within the bounds proposed by
Aydan (2001) and Aydan and Ohta (2011).

Fig. 7 Comparison of estimations by several attenuation relations with observations

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STRUCTURAL DAMAGE
The earthquake resulted in heavy damage to buildings and significant casualties in this province,
particularly in Erciş. A number of 6-8 stories RC buildings collapsed particularly in Erciş and Van(Photo 3). The major causes of the heavy damage to reinforced concrete buildings were basicallysimilar to the observations in previous earthquakes such as poor quality of construction materials, lackof implementation of design codes, existence of soft-floor (weak-floor), pounding, lack of ductility,
poor integrity of RC frame with in-fill walls, poor quality of workmanship and poor ground conditions.
It should be added that site effects most likely contributed to alteration of frequency characteristics ofthe ground motions to adversely affect the buildings. There are available borehole logs but the depthsof the logs are shallow and the depth to bedrock is not known.
Buildings in rural areas and villages are of brick masonry or stone masonry type (Photo 4). Whenthese buildings are constructed with the consideration of having a mat concrete or firm base, light roof,
hatıl (timber or conrete confining beams) at certain intervals, lime (cement)-based bonding, utilizationof saman (straws) in kerpiç (adobe) bricks and plastered walls, the damage was none or slight. Suchbuildings performed very well even some permanent ground deformation occurred beneath theirfoundations. The bridges are generally constructed using cast-in place technique. The earthquake
caused very little damage to bridges. The damage was due to the settlement of piers and settlement andlateral deformation of approach embankments (Photo 5).
Some ground liquefaction occurred at Van port and there were some slight cracking to RC
components and deformation of railways (Photo 6). Nevertheless, the port was functional.
There are several rock-fill dams up to 65 m high and earth-fill water reservoirs in the epicentral area.
The earthquake did not cause any damage to the dams even some of them were very close to theearthquake epicenter.

39.026627, 43.364292

39.026627, 43.364292

Photo 3 Views of collapsed RC buildings and detailing of RC elements

1910

38.597252, 43.249016

38 674739 43 243389

38.740503, 43.312805

Photo 4 Views of heavily damage brick masonry buildings

38.657834, 43.30626

Photo 5 Views of slightly damaged Tirleşin bridge over Karasu on Van-Ağrı Highway

1911

Photo 6 Views of slightly damaged Van port (all photos at around 38.516441, 43.308368)

CONCLUSIONS
The following conclusions may be drawn from the previous sections:(a) This earthquake was caused by thrust type faulting, which is generally rare for Turkey, but it istypical of faulting mechanism for this tectonic province of Turkey.
(b) The strong motions induced by this earthquake has a strong directivity effect and Erciş town witha population of 100,000 people suffered heavy damage and casualties as it was on the hanging
wall side of the fault.
(c) The main causes of heavy damage or collapse of reinforced concrete buildings are similar to thoseobserved in previous earthquakes occurred in Turkey. This earthquake also showed that thenon-structural repairs of buildings are disastrous and must be avoided.
(d) Except buildings, the damage to common civil engineering structures such as roadways, bridges,
tunnels and dams was almost none or slight.
As a result of the observations, it is strongly suggested that the construction practices in earthquake
prone areas of Turkey be changed from that of reinforced concrete moment framed system toreinforced concrete shear-wall system. Such a change would reduce drift ratios and prevent collapse ofbuildings, thus averting loss of lives and property.

ACKNOWLEDGMENTS
The authors sincerely acknowledge the information and guidance given by Ş. Öztürk (Van 100. Yıl
University and Chairman of Van Branch of the Chamber of Architectures of Turkey) duringreconnaisance visit to the earthquake affected region. The most findings described here are theoutcomes of the survey by the Turkish and Japanese experts dispatched by the Japan Society of Civil
Engineers (JSCE). In organizing the team, the Disaster-Information Network among JSCE, AIJ and
JAEE (Chairman, Prof. K. Kawashima of the Tokyo Institute of Technology) took the initiative.

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