Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

Dedicated to Dr. Atsushi Miyazaki and the people lost their lives in this earthquake

THE CHARACTERISTICS OF THE TRIGGERED 2011
VAN-EDREMİT EARTHQUAKE AND INDUCEDDAMAGE
Ömer AYDAN1, Halil KUMSAR2, Reşat ULUSAY3, Onur KÖSE4 and Mehmet ÇELEBİ5
1

Professor, Ocean Research Institute, Tokai University, Shizuoka
aydan@scc.u-tokai.ac.jp
2
Professor, Department of Geological Engineering, Pamukkale University,Denizli, hkumsar@pamukkale.edu.tr
3
Professor, Department of Geological Engineering, Hacettepe University,Ankara, Turkey, resat@hacettepe.edu.tr
4
Assıstant Professor, Department of Geological Engineering, Yüzüncü Yıl UniversityVan, Turkey, onurkosevan@gmail.com
5Senior Research Civil Engineer, USGS,
Menlo Park, USA, celebi@usgs.gov

ABSTRACT: The Mw=5.6 magnitude Van-Edremit earthquake occurred at 21:23 local
time on November 9, 2011(USGS (2011)), was caused by a fault having a strike-slip
mechanism. The earthquake was triggered by the effect of the stress state of the Mw 7.1
Van-Erciş earthquake on October 23, 2011 and it caused heavy damage and collapse ofadditional 30 buildings and 38 additional fatalities particularly in the city of Van, which
was severely shaken by the earlier earthquake. . This paper outlines various aspects of thetriggered earthquake.. Following a brief outline of geology, seismo-tectonics andgeotechnical conditions in Van City, an evaluation of strong ground motion
characteristics and structural and geotechnical damage are described and the findings andlessons learned from this earthquake are presented.
Key Words: Van-Edremit earthquake, geology, strike-slip faulting, high ground motions,structural damage, liquefaction

INTRODUCTION
Van- Edremit earthquake occurred at 21:23 local time on November 9, 2011. Although the moment
magnitude (Mw) of this earthquake was only 5.6, it caused heavy damage in the city of Van and added
to the distress caused by the earlier Mw 7.1 Van-Erciş earthquake on October 23, 2011. The epicenterof this earthquake (38.4288N, 43.229E) is located near Edremit, a town on the eastern shore of Van
Lake about 16 km to the south of Van city center. This earthquake is considered to have been triggeredby the effect of the crustal stress state of the October 23, 2011 event.
Van-Edremit earthquake caused very high ground accelerations in the City of Van, and resulted incollapse of 30 additional reinforced concrete buildings, most of which had suffered substantial damage
during the 23 October 2011 earthquake. Fortunately, 23 of the collapsed buildings had been evacuated1914

due to the damage caused by the October 23, 2011 earthquake. However, two hotel buildings wereopen during this second earthquake and some of the people staying there lost their lives. The total
casualties and injured people caused by this earthquake are 38 and 30, respectively.
This earthquake also caused some ground liquefaction along the Van lakeshore and the groundliquefaction again occurred at the Van port, where the ground liquefaction was also observed following
the 23 October 2011 earthquake.
This paper outlines various aspects of the Van-Edremit earthquake of November 9, 2011. In thefirst part of the paper, brief outlines of geology, seismo-tectonics and geotechnical conditions in Van
City and its close vicinity are given. The second part involves seismic characteristics of the earthquakeand evaluation of strong ground motion characteristics. The third part describes both structural andgeotechnical damages, and the effect of non-appropriate repair of the buildings is also discussed. In thefinal part, the findings and lessons learned from this earthquake are summarized.

GEOLOGY AND GEOTECHNICAL CONDITIONS
Fig. 1 shows the geological conditions of the City of Van and its close proximity. Van is mainly locatedover a mainly alluvial fan (Qey), and the area along the lakeshore and in the vicinity of Karasu Riveris mainly composed of recent alluvial deposits (Qa). The shear wave velocity of alluvial deposits ofrecent alluvial deposits (Qa) is estimated to be ranging between 250-300 m/s while the shear wave
velocity of alluvial deposits (Qey) is about 350 m/s. The town of Edremit, close to the epicenter, islocated over travertine deposits (Qpltr).
There are several types of faults in the epicentral area. Besides main thrust faults trending E-W,
there are conjugate strike-slip faults with some normal components. Özkaymak et al. (2004)
recognized NW-SE and NE-SW trending strike-slip faults. Alabayır fault is one of such faults.

Fig. 1 Geology of Van and its close vicinity and faulting mechanisms for the Van-Edremit earthquake
estimated by different institutes (base map from Özkaymak et al., 2004)

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FOCAL MECHANISM AND SEISMICITY
Fig. 1 also shows the focal mechanisms obtained by USGS (2011), ERD (2011), KOERI (2011) andHARVARD (2011). All focal mechanisms solutions indicated that the faulting mechanism of thisearthquake was due to strike-slip faulting. Although the solutions yield two fault planes, NW-SEtrending fault may be the causative fault. In view of the seismicity since November 09, 2011 shown in
Fig. 2 and recognized fault traces in the field, a sinistral NW-SE tending steeply dipping fault shouldbe the causative fault. This fault probably is located to the east of Edremit.

Fig. 2 Seismicity of epicentral areas of Nov. 09, 2011 and Oct. 23, 2011 since Nov. 09, 2011CHARACTERISTICS OF STRONG MOTIONS
During this earthquake, strong ground motions were recorded by National Strong Motion Network ofTurkey operated by the Earthquake Research Department (ERD) and temporarily installed network byKandilli Observatory and Earthquake Research Institute (KOERI) following the October 23, 2011
Van-Erciş earthquake. KOERI also installed strong motion stations on both soil (VNKEA) and rock(VNS). The maximum ground acceleration recorded by the ERD (VBIM) and KOERI (VNKEA) attwo soil ground sites in the City of Van are 0.27 g and 0.29 g, respectively (Fig. 3). Fig. 4 compares
the acceleration records and acceleration response spectra of motions recorded at soil stations while
Figure 5 compares recorded motions and corresponding spectra at soil (VNKEA) and rock stations

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(VNS). Although the amplitudes of waves are slightly different, the records are quite similar to eachother. Furthermore, the accelerations are amplifed for periods of 0.1-0.15s and 0.35-0.4s.

Fig. 3 Locations of strong motion stations (base map from Google earth)Fig. 4 Comparison of (a) acceleration records and (b) their acceleration response spectra ofVBIM-ERD and VNKEA-KOERI stations in Van

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Fig. 5 Comparison of the acceleration records and their acceleration response spectra on soil(VNKEA) and rock (VNS) stations in Van
The comparison of raw acceleration records and their acceleration response spectra indicated thatthe amplifications were 2.4 and 3.6 times, respectively. Furthermore, the maximum spectral
accelerations roughly correspond to those of periods of 0.36-0.4 s, which generally corresponds to thenatural periods of 6-8 story reinforced concrete buildings.
Fig. 5 shows the attenuation of strong motions recorded by the ERD and KOERI with theempirical relations of Aydan (2001), Aydan and Ohta (2011a) and Ulusay et al. (2004). The maximum
ground acceleration on soil is well predicted by the attenuation relation proposed by Aydan (2001)
while the relations by Aydan and Ohta (2011a) using the shear velocity of Van strong motion stationand Ulusay et al. (2004) underestimated the maximum ground accelerations by 30-40% less.
One of important observations in Fig. 5 is the effect of the fault orientation. While Edremitstation is on the stationary or footwall, Van station is on the mobile or hanging wall side. Themaximum ground accelerations are almost same, the distances of the Edremit and Van strong motion
stations to the fault are 4 and 12 km, respectively. This fact also illustrates the fundamental reason forseemingly scattering of observed data when spherical and cylindrical attenuation relations areemployed.
Aydan and Ohta (2011a) improved the attenuation relations of Aydan (2007) by considering the dip
angle and fault length also. The attenuation relations of Aydan and Ohta (2011a) for maximum ground
velocity are compared in Fig. 5. The computed maximum ground velocity values at Edremit, Muradiyeand Bitlis are well estimated by the attenuation relations of Aydan and Ohta (2011a). However, theobserved value of Van strong motion station is somewhat higher than the estimations when the shear
wave velocity (Vs30) of 363 m/s is used. Therefore, the concept of using the shear wave velocity for top
30 m ground as the representative value of site conditions is very questionable. Similar conclusion isvalid for the records taken in Japan.

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(a)(b)Fig. 5 Comparison of some empirical attenuation relations for maximum ground acceleration andmaximum ground velocity with observations
Aydan and Ohta (2011b) modified slightly their original method called EPS method (Ohta andAydan, 2007) to estimate the behavious of ground during earthquake and to compute the permanent
ground deformation from strong motion records. This method wass applied to near field stations,specifically VBIM-ERD, EDR-ERD, VNS-KOERI and VNKEA-KOERI, around the epicentral area
Fig. 6(a) compares the responses for three different directions in the City of Van, which is located on
the mobile side of the fault. It is interesting to note that the top soil may even move opposite direction
compared to that of rock base. This further implies that ground shaking may cause the plastic
deformation of top soil layer.

Fig. 6 Displacement responses of strong motion stations computed from EPS method (a) The City ofVan), (b) Rock ground at Edremit and Van

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Next the deformation responses of stations (EDR-ERD and VNS-KOERI) located over rock arecompared as shown in Fig. 6(b). If the mobile side of the N-S trending fault is the east block, the strike
slip faulting implies that there should be considerable permanent ground displacement at VNS-KOERIstation as compared with that at EDR-ERD station. The net permanent displacement of theVNS-KOERI is about 37 mm northward while that of the EDR-ERD is almost nill. This conclusion
may also be of great value to explain why there was huge damage in the City of Van as compared tothe light damage in Edremit.

CASUALTIES AND STRUCTURAL DAMAGE
This earthquake resulted in the loss of 38 lives as it happened at 21:23 in the evening. On the otherhand, the 23 October 2011 Van-Erciş earthquake resulted in the loss of 604 people and occurred at
13:41 on Sunday. Fig. 7 shows the relations between local magnitude and casualties. The estimations
for upper (UL), mean (ML) and lower (LL) limits are computed from the following function proposedin this article using the data from various catalogues for Turkey (i.e. Ergin et al. 1967; Soysal et al.
1981; Eyidoğan et al. 1991).

N = A( M L − B) c(1)The values of constants A and c are 2 and 7, while the values of constant B are 3.5, 4.5 and 5.5 for UL,
ML and LL, respectively. The main reason for such large ranges may be related to the time ofearthquake, quality of buildings and ground conditions.

Fig. 7 Relation between local magnitude of earthquakes and casualties
This earthquake caused the collapse of the 30 reinforced concrete buildings, most of which had
already suffered substantial damage during the 23 October 2011 earthquake (Photos 1, 2 and 3).
Fortunately, 23 of the collapsed buildings had been evacuated due to the damage caused by the earlier

1920earthquake. However, two hotel buildings were open during this second earthquake and some of thepeople staying there lost their lives. This earthquake also caused additional damage to some buildings.
The collapsed hotels had cracks following the October 23, 2011 earthquake and they werecosmetically repaired. The authors noticed such non-structural repairs in the City of Van during theirreconnaissance for the October 23, 2011 earthquake (Photo 4).

Photo 1 Views of Bayram Otel before and after the Van-Edremit earthquake (Anadolu Ajansı, 2011)

Photo 2 Views of a collapsed reinforced concrete building in Van (Anadolu Ajansı, 2011)1921

Photo 3 Views of heavily damaged reinforced concrete buildings of DSI in Van

Photo 4. Cosmetic repairs applied to a damaged RC building in Van on November 5, 2011 after theVan-Erciş earthquake

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The major causes of the heavy damage to reinforced concrete buildings were basically similar to theprevious observations during previous earthquakes in Turkey:(a) Quality of construction materials,(b) Lack of implementation of design codes (bars, stir-ups, proper column-beam connections, tie-beams,
good foundation etc.),(c) Existence of soft-floor (weak-floor),(d) Pounding,(e) Lack of ductility,(f) Poor integrity of RC frame with in-fill walls,(g) Quality of workmanship.
(h) Poor ground conditions.
Furthermore, cosmetic non-structural by re-plastering of cracked beams, columns, infill-walls and beamcolumn connections had disastrous effects. Similar problem was observed in buildings damaged by the1999 Kocaeli earthquake in Düzce during the 1999 Düzce earthquake (Aydan et al., 2000a and 2000b).

GEOTECHNICAL DAMAGE
This earthquake also caused some ground liquefaction along the Van lakeshore (Photo 5) and theground liquefaction again occurred at the Port of Van, where the ground liquefaction was also
observed following the 23 October 2011 earthquake. This is probably the smallest magnitude
earthquake to cause liquefaction in Turkey so far. Fig. 7 shows the grain size distribution of the boiled
sand, which is within the most liquefiable bounds with high percentage of fine content.
Fig. 8 shows the empirical relations proposed between earthquake magnitude (Mw) andhypocentral distance of liquefaction location proposed by Aydan et al. (1998) and Aydan (2007) withthe observation in this earthquake. The observation is within the proposed empirical limits.

Photo 5 Views of boiled sand in Van port due to the M5.6 earthquake

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Fig. 8 Grain size distribution of boiled sand sample obtained from Port of Van immediately after theM5.6 earthquake

Fig. 9 Comparison of empirical relations with observationCONCLUSIONS
The following conclusions may be drawn from the previous sections:(a) This earthquake is not an aftershock of the October 23, 2011 Van-Erciş earthquake. It has
different faulting mechanism. However, there is no doubt that it was triggered due to the variationof crustal stresses induced by the October 23, 2011 earthquake.
(b) Although the magnitude of this earthquake was small, high ground motions with a strong
directivity effect were recorded. The maximum ground accelerations on soil ground were
amplified up to 3.6 times that on rocky ground.
(c) The main causes of heavy damage or collapse of reinforced concrete buildings are similar to thoseobserved in previous earthquakes. This earthquake also showed that the cosmetic non-structural
repairs of buildings are disastrous and must be avoided.

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(d) Van-Edremit is probably the smallest magnitude earthquake to cause liquefaction in Turkey so far.
Furthermore, this earthquake caused ground liquefaction in the same location again.

ACKNOWLEDGMENTS
The authors sincerely acknowledge the information and pictures provided by Mr. Ayhan Koçbay
from DSI on damage to their buildings in Van.

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