Varto Earthquake: 19 August 1966

Bulletin of the Seismological Society of America. Vol. 58, No. !, pp. 47-102. February, 1968

THE VARTO UST~KRAN (ANATOLIA) EARTHQUAKE OF 19 AUGUST

1966

SUMMARY OF A FIELD REPORT

BY N. N. AMBI~ASEYS AND A. ZATOPEK

ABSTRACT

The Varto-0stiJkran earthquake of August 19, 1966, occurred near the east end of the Anatolian fault system in Turkey, very near where an earlier, less intense earthquake had caused damage in 1946. The earthquake had a magnitude 6.8 and it was felt over an area of over 300,000 square kilometers. The epicentral intensity did not exceed IX (MM) and there were signs of faulting over a length of about 30 kilometers. The earthquake killed some 2,500 and wounded 1,300 people. Over 19,000 houses of poor construction were destroyed and 100,000 people were made homeless.

INTRODIYCTION

Following the earthquake of 19 August, 1966, in Eastern Anatolia (Turkey) UNESCO organized and dispatched a reconnaissance mission to the epieentral area. The main objective of the mission, which was composed of the Writers, was to make a preliminary study of the seismological and engineering aspects of the earthquake, and to draw up plans for an eventual study mission. The mission also aimed to assess the damage caused by the shock and to assist the authorities in planning research and training in the fields of seismology and earthquake engineering.

This paper is a summary of the field report submitted by the authors to Unesco (Ambraseys, Z£topek, 1966). It gives an account of the effects of the Varto- t~stiikran earthquake of 19 August, 1966, in the epicentral region which was visited by the writers.

Figure 1 shows the general trend of the North Anatolia system and the extent of faulting after 1938. Solid lines indicate the main course of the faults that were associated with particular earthquakes and for which undisputed evidence of relative movement can be established. Dashed lines show the trend of faulting deduced from secondary surface effects which in most cases were mixed with features that were difficult to separate from those caused by gravity, such as incipient slides on slopes with strikes trending along the axis of the established faults. I t is of interest to note from this figure the remarkable trend of the suc- cessive faulting along a length of over 800 kilometers having consistently right lateral strike-slip, with the downth ro~ side to the north.

I t is also of interest to notice the time sequence of the shocks associated with these fault movements which is shown in the same figure by the numbers attached to the epicenters. In fact, this sequence becomes more regular if shocks west of Edremit as far as the Ionian Islands in western Greece are included. Table 1 gives the main characteristics of earthquakes with M -> 6 that occurred since 1909 along the Anatolian fault system.

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VARTO "USTtTKRAN EARTHQUAKE OF 19 A V e V S T 1966 49

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From this table we notice that ~ t h the exception of the earthquake of 1909 which was not documented, and of the shock of October 1944 which had its epicenter at sea, every other earthquake along the Anatolian fault system of magnitude equal to or greater than 6} has been associated with faulting.

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A: M >- 7½ or I = X B: 7{ > M > 6} or I X ~ I < X

C : 6} > M > 5½ or V I I ~ I < I X D:5½ > M > 4 or V < I < V I I F: E v e n t s pr ior to 1901 (Historical)

For these earthquakes we found that the relation between magnitude and length of faulting L can be expressed by

M = 5.62 + 0.88 log L (1)

and that the seismic energy released by these shocks can be expressed in terms of the length of faulting either by

E = 2.1 X 1020 L '~6 (2)

VARTO "USTUKRAN EARTHQUAKE OF 19 A V G V S T 1966 51

or by

E = 1.7 X 1020 L 1'82 (3)

depending on whether we chose B£th's or Gutenberg's magnitude-energy rela- tionship (B&th, 1958) to eliminate M from (1). For all practical purposes, however, this choice is immaterial as (2) and (3) are almost identical.

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FIG, 3. Damage distribution; earthquake of 7 March 1966• A: 90%-100% of adobe houses destroyed or damaged beyond repair B: 50%-89% of adobe houses destroyed or damaged beyond repair C: 11%-49% of adobe houses destroyed or damaged beyond repair D: 5%-10% of adobe houses destroyed or damaged beyond repair E: Villages without serious damage•

It is of interest to notice that the constants in (1) are practically identical to those derived by Toeher for California (Tocher, 1958) and that the difference of (2) or (3) in their constants from the corresponding relation that Tocher derived is because he chose to eliminate M from (1) using De Noyer's energy relation. The exponent of L either in (2) or (3) is now noticeably closer to one rather than to two, a value found by Tocher. This suggests that the linear dimensions of the

52 BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA

focal volume do not increase in the same proportion with increasing energy con- tent, but that the volume of the strained upper crust tends to e]ongate in the direction of faulting with increasing length of the rupture• This is more plausible

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FIG. 4. Damage distribution; earthquake 12 July 1966. Full dots show villages seriously damaged. Open circles: small damage. Dots show localities damaged by the earthquake of 7 March 1966.

than Tocher's suggestion that the volume of the strained rock is not thicker for the largest shocks than for the smallest shocks that produce a fault trace.

In the report (Ambraseys and ZKtopek, 1966), we concerned ourselves also with the study of the seismicity of the extreme east part of the Anatolian fault system which is comprised between 38 ° to 40 ° Nor th and 39 ° to 42.5 ° East (insert in Figure 1). The purpose of the study was mainly t o see whether any particular trend of

VARTO USTUKRAN EARTHQUAKE OF 19 AUGUST 1966 53

seismic activity in the Varto region could be established. The results are shown in Figure 2.

From this figure it appears that the epicenters of the strongest shocks follow an east-southeast axis from Ercincan to Karhova and from Varto to the Lake Van, cutting obliquely the Taurides between KiWi and Mu~, extending towards the Mu~-Van depression. This axis coincides with a zone of remarkable offsets of the rivers Firat and Murat (ABCD). There seems to be no indication, at least within the region studied, of a southwest trending concentration of epicenters that may

TABLE 2

Epicenter Date Time I0 M References

Micro- Macro-

1966 Aug. 19 1222 39°.2-41°.6 39°.20-41°.35 IX 6.8 BCS, CGS, P R 1315 39.2-41.1 39.20-41.15 VII 5.1 CGS, BCS, P R 1354 38.9-41.7 38.95-41.65 VII 5.3 CGS, BCS, P R 1403 39.2-41.3 - - 4.6 BCS, CGS 1417 39.3-41.1 39.15-41.12 VI 5.0 CGS, BCS, P R 1841 39.1-41.4 39.10--41.35 VII 4.7 BCS, CGS, P R

20 1 1 5 9 39.5-40.9 39.30-41.00 6.2 BCS, P R 1201 39.0-40.9 - - 5.4 CGS 1517 39.6--40.3 - - BCS 1754 39.3-41.2 - - 4.4 CGS

21 0015 39.2-41.8 39.24-41.75 VII 4.8 BCS, CGS, P R 0225 39.3-41.9 - - 4.7 CGS 1517 39.3-41.7 - - BCS 2236 39.3-41.4 - - BCS

23 0135 39.2-41.0 - - 4.6 CGS, BCS, MOSC Sep. 10 1009 39.2-41.4 39.25-41.75 VI 4.5 CGS, P R

13 2 0 2 3 38.9-40.6 - - 4.5 CGS 17 1 9 4 2 39.3-41.9 39.20-41.30 V 4.0 CGS, BCS, P R 19 0 2 0 3 38.4--42.7 - - 4.9 CGS 29 1459 - - 39.10-41.30 V P R

Oct. 1 0015 - - 39.30-41.70 VI P R 6 0748 39.3-41.9 - - 4.6 CGS

suggest a connection between this part of the Anatolian fault and the Jordan rift system. Nor is there any indication of high seismieity in the Irandides or to the South.

The earthquake of 19 August, 1966, occurred near the extreme east end of the Anatolian fault system, not far from where an earlier but less intense shock occurred in 1946, Figure 1. It is not certain whether this segment, west of Lake Van, is the point where the north Anatolian fault ioins the Jordan rift system or whether the former continues to the east, branching off not before reaching the Zagros-Elburz abutment in Iran (Allen, 1966; Pavoni, 1961). This is an important question but we need not enter into it here; we clearly need more data on what is happening between Erzurum and MMatyla-Maras.

54 :BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA_

FORESHOCKS

Six months before the earthquake of August 19th, the area between ttmls and Mu~, was shaken by an earthquake which was strong enough to cause general concern. This earthquake was followed by numerous aftershocks which five months later culminated in another strong earthquake that caused a4ditional damage, killing a number of people around TepekSy.

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FIG. 5. Map showing aftershocks in the epicentral area. Numbers refer to Table 2.

The first of these earthquakes occurred on the 7th of March, 1966, at about 0316 local time (0116 GMT) and Caused considerable damage along the I-Imts- TepekSy road. According to press-reports and from information collected locally about 15 people were killed and 30 wounded. Out of 13,000 houses affected over 4,000 were completely destroyed and 3,600 were damaged. Figure 3 shows the distribution of damage cafised by this shock. This information about the effects of the earthquake is, however, incomplete as at the time many villages in the stricken area were completely cut off by snow and never reported fully their actual condi-

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tion. In Figure 3, full dots represent villages that suffered most; open circles show villages that were damaged. The shock which lasted about 3 seconds, was felt within an area of about 60,000 square kilometers. Two strong aftershoeks at 0357 and 0415 local time caused some additional damage near Tepek6y. The instrumental epicenter as determined by the USCGS lies just south of A~gelin.

The seismic activity then moved slowly to the southeast with numerous shocks southeast of Bitlis. The largest of these occurred on 2nd May at 2313 hours GMT and caused considerable damage at Hizan, 35 kilometers southeast of Bitlis.

Then, on the 12th of July, a large shock occurred at the southern end of the area that was damaged by the shocks of March. I t caused considerable damage around ~arbuhur (Ba~i~i) where 12 people were killed and 20 wounded. Figure 4

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FIG. 7. P lan of Hmls Regional School. A: Cracks in the plas ter ; B: Cracks in the ground.

shows the distribution of damage caused by this earthquake. Dots on this figure show localities damaged by the March earthquake. The shock was a sharp jolt, lasting only 2 seconds, and it was not felt very far. I t caused, however, a long fracture in the ground which, starting just north of TepekSy, extended for about one kilometer crossing the ~arbuhur River in a N 60°-E direction, as indicated by the dashed line in Figure 4. A farmhouse straddling this crack, on the east side of the river, was destroyed. The instrumental epicenter determined by Strasbourg (BCIS) is situated just north of Tepek6y.

These two shocks were most probably premonitories of the main earthquake and occurred to the east of the area that was affected by the shock of August 19th. At the same time as these earthquakes it appears from press-reports that a number of damaging shocks occurred 50 kilometers northeast of A~gelin and two others around Bitlis. These were too small to be registered by the regional network.


THE VARTO-~STOKRAN EARTHQUAKE OF 1966

On August 19th, 1966, at about 14 hours 22 minutes local t ime (1222 GMT) , eastern Anatolia was shaken by a severe earthquake. The epicenter of the shock

FIG. 8. Hmls Regional School. Distortion of column (arrow).

was computed by a number of seismological centers with the following results:

USCGS Strasbourg* Moscow

39.2°N-41.7°E 39.2 ° 4- 0.06 N-41.6 ° 4- 0.05E 39.1°N-41.6°E.

The earthquake was felt with an intensity equal to or greater than I I I (NIM) over an area of about 300,000 square kilometers, and showed a maximum intensity which did not exceed I X (MM).

* Private communication by Prof. J. P. Roth4, Strasbourg.

58 :BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA

The magnitude of the shock calculated by various stations varied between 6.4 and 7.7, with an average value of about 7.0. A special study of the magnitude carried out at the Charles University in Prague showed that the most probable value is M = 6.8.

The focal depth of the earthquake was computed by the USCGS at about 26 kilometers, and by the BCIS at about 50 kilometers. From macroseismic data, (Sponheuer, 1965) however, the value of the focal depth calculated by the writers suggests only about 10 kilometers.

FIG. 9. Hmls Regional Hospital after the earthquake of August 19. Long axis bearing N 60°E. Arrow shows view in Figure 10.

The seismic activity of August, 1966 was associated with ground displacements Mong the Varto-Ustiikran axis which appeared in the form of secondary ground effects. Preliminary results from a fault plane solution indicate right-lateral strike slip movement and a dip of 83 ° towards N 35°-E.

In the days following the main shock, numerous aftershocks were felt; some of them causing additional damage, and quite a few being registered by seismic stations of the international network.

The main shock and its aftershocks affected an area with a total population of 217,000 and 34,000 houses. The earthquake killed 2,520 and wounded 1,370 people destroying or damaging beyond repair about 19,000 houses mainly of adobe construction, and made over 100,000 people homeless.*

* The statistics are based on data supplied by the authorities in Erzurum and in Ankara shortly after the earthquake.

VARTO ti-ST'UKRAN EARTHQUAKE OF 19 AUGUST 1966 59

AFTERSHOCKS

At the time of writing (November, 1966) it is premature to attempt a synthesi s of the aftershock characteristics because the data are, at this stage, incomplete. We do, however, have some material which allows some general observations to be made concerning the general pattern of aftershock sequence.

The nearest station is over 400 kilometers from Varto and only a small number of the aftershoeks has been registered by the international network. The coordinates of the shocks determined either by the USCGS or the BCIS in Strasbourg are listed

FIG. 10. HlnlS Regional Hospital. Ring beams and floor beam cast short of supporting corner brick pier.

in Table 2 and their location with respect to the position of the main shock is shown in Figure 5. Although a proper study of their sequence is at this stage unwarranted, it is of interest to notice that these shocks showed a marked tendency not to report from the same epicenter. The numerals in Figure 5 represent their time sequence during the first seven weeks after the main shock. From this figure it can be seen that aftershocks have been alternating between the extreme positions of the Varto- ~stiikran-Karhova axis, the largest shocks occurring to the northwest, away from the area of the foreshock activity, but also along a northeast trending axis in the Mus-Hlms direction. At the moment the aftershock area is about 4 X 1013cm. 2 and aftershocks have released over 40 per cent of the strain released by the main shock.

60 B U L L E T I N OF T H E S E I S M O L O G I C A L SOCIETY OF A M E R I C A

DAMAGE

Starting from Erzurum on the way to Kars, some damage to the poorest type of houses was noticeable. In Erzurum, about 90 kilometers from the epicenter, 20 adobe houses collapsed and another 190 of the same type were damaged. The city had been shaken a number of times with some damage prior to the 19th of August. That damage was further aggravated by heavy rains and lack of repairs and many adobe houses are known to have collapsed without the assistance of an earthquake. Better built houses in Erzurum suffered minor cracks while reinforced concrete buildings withstood the shock without any damage. No chimneys were thrown

FIG. 11. ttmls. Damage to reinforced concrete framed house.

down and with the exception of two cases where the ornaments at the top of a minaret were dislodged, no minarets were damaged.

Villages along the 60 kilometer-long road to Kars as far as K6prSkSy (~obandede)* suffered similar damage. Occasional slides on steep slopes were noticed but these were soon found to be common features of the physiography of the marls in east Anatolia.

From I~SprSkSy we turned south on the road to Hmls, following the course of the river Aras. For the next 60 kilometers the road crosses a sparsely populated country, climbing up over passes at an altitude of just under 1,800 meters. The damage observed in villages as far south as Asay SSylemez was small but as we approached the plateau of HaclSmer it slowly increased. Along this route it was not possible to find vibrational effects suggesting intensities greater than V (IVan).

* Most places in the region of Varto have two names, one in Turkish and a different name in Kurdish.

VARTO iJSTrJKRAN EARTHQUAKE OF 19 AUGUST 1966 61

In a number of cases, enormous columns of weathered rocks were still standing, delicately poised at the base.

Before reaching HlnlS, about 10 kilometers west, off the main road, there was some indication of high local intensity, perhaps reaching VII. Also near Tapu (Tapikomu), a village about 13 kilometers north-northwest of Hmls rockfalls and shattered outcropping rocks showed a zone of intense ground movements. The village of Tapu, Figure 6, which is situated at the base of an exposed wall of columnar basalt, was obliterated, not so much by the actual shaking of the ground as by the rockfalls.

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FIO. 12. A~gelin. Collapsed school; two houses of similar construction (arrows) shattered but still standing; brick chimneys undamaged.

At HnHs, a town of about 5,000 inhabitants, the damage was considerable but very erratic. Of the total 950 houses of all types, 347 collapsed or were damaged beyond repair and 450 were damaged. Adobe constructions and dry rubble or masonry suffered most. What was so erratic, not only in IImls but also in the rest of the region, was the widely different resistance that various types of local construction could offer. This was perhaps influenced by the previous shocks of l~{arch and April.

Forty newly-built, mostly brick building of the Hmls Regional S3hg~l (IImls B61ge Okulu) showed no signs of serious damage; cracks in the plaster in sgm~ of the brick structures and hair-cracks in a number of reinforced concrete fram~ sbruc- tures was all that could be found. Figure 7 shows a plan of the s3hool which is situated in the north entrance to the town on a flat plain of soft alluvium. B~cause of the soft ground and high water table, some of the structures were built on rein-

62 BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERIC2~

forced concrete mats. A close inspection revealed some cracks in the plaster of buildings 3, 4, 6, 8, and 9 which followed the mortar joints of the panels between the windows. Buildings 2 and 3 suffered minor cracks and many open fissures were found in the ground adjacent to the south and east side of their foundations. Building No. 14, the recreation hall, a reinforced concrete structure with ten frames spanning 16 meters, was found to be more damaged than any other of the buildings. Numerous hair-cracks were found at the base of the columns and also at girder joints. Where such groups of cracks were found it appeared as if the concrete had increased in volume locally, bulging slightly. A 26 meter-high elevated watertank supported by a steel frame was empty at the time of the earthquake but

FIG. 13. Varto. General damage in old village. Slightly damaged modern brick bungalows, (arrow).

it showed some distortion which may be due to faulty construction rather than overstressing.

On the left, entering the old town, the Regional Hospital was destroyed. I t was a two-story wall-bearing construction with a masonry basement. Slender reinforced concrete columns supported the heavy tie-beams between every second window opening, the other support in between being a brick panel. The floors were cast in situ reinforced concrete slabs supported by heavy beams which were resting on thick brick walls. Figure 9 shows the two-thirds of the hospital which was still standing but unsafe to enter. The rest of the structure was thro~nl out by the earthquake and was totally destroyed. The interior walls were shattered to the verge of collapse. An inspection revealed that the structure contained many bad details and that the materials used were of very low quality. Brick walls 45 to 50 centimeters thick were built of massive lime-cement bricks which were too


heavy and of very low strength. The mortar was thick and contained very coarse aggregates and the brickwork was unbounded. As Figure 10 shows, the wall beams were cast short of their supporting corner brick columns. In contrast to the superstructure, the basement suffered practically no damage. Nor was there any sig- nificant damage to the neighbouring one-story brick houses, which remained in use.

Nearby, a one story reinforced concrete frame construction, shown in Figure 11, suffered some damage to the filling walls, which were detached from the frames and part of a panel collapsed.

FIG. 14. Varto. Adobe construction; diagonal cracks between doorway and windows start where timber ring-beam is improperly spliced.

A few hewn-stone masonry constructions in the old part of Hams crumbled. These were of a very old type of construction already weakened through ageing and insufficient repairs

The damage to the few properly built houses in Hires, as in the case of the Ilegional School, was small and was mostly confined to the exterior plaster of the walls of ground tic ors. In thins few chimneys collapsed, and terraced ground with small retaining walls did not show any signs of sliding. The ornaments at the top of a minaret fell but neither the minaret itself nor the mosque suffered any damage.

As we approached Varto (Gtimgtim), to the southwest and southeast of Hmls the villages that we visited showed an increasing intensity though not uniformly with distance from the epicentral area. Here we were in the region damaged by the earthquake of March 7th, and its effects had produced a distortion in the distribution of damage caused later by the Varto earthquake. Between Hmls and Varto there are no man-made structures other than those of adobe and, therefore,


there was little evidence which could serve as a measure for assessing intensities. The cumulative effects of the foreshocks and of the main shock were very serious. In some cases the damage was so heavy that no distribution could be made between total destruction arid heavy damage.

A~gelin (Akgelin), for instance, a small village 18 kilometers south-southeast of Hmls and 25 kilometers from Varto, was completely wiped out. During the shock of March 7th, it was heavily damaged, and according to local information and press-reports, two people were killed and many of its adobe houses were made unsafe to enter. Now the village, with its 75 houses destroyed and 21 people killed, was a heap of rubble. The site where the village is built is on a knoll of weathered

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FIG. 15. Var to . H o l l o w - b r i c k c o n s t r u c t i o n .

basalt, on the southwest side of which there were three stone masonry constructions, the local school and two small houses. Figure 12 shows the ruins of the former; the masonry walls which supported a heavy reinforced concrete tie-beam were laid in a cement mortar in which it seems that soil had been used in lieu of sand. At the first shock of the August 19th earthquake the two portals sunk in the middle forcing the longitudinal wails to spread out. A few meters away, another house was shattered but did not collapse. The masonry came apart and the interior walls disintegrated along their mortar joints. Nevertheless, the two brick chimneys were left undamaged. A series of discontinuous fissures in the ground crossing the ruins of the village were found to merge on the other side and terminate in a suc- cession of small shallow slides.

Approaching Varto from the north-east, villages near A~gelin that also suffered from the March 7th shock, such as Zolokmu (Ko~yata~l) and Divanhiiseym, were

VAI~TO USTUKRAN EARTHQUAKE OF 19 AUGUST 1966 65

found to be less damaged and many abode houses were left standing but damaged beyond repair. Rock falls, mostly from outcropping basalts, had strewn gentle slopes with boulders of different size.

Varto is the administrative center of the region and has about 2,500 inhabitants. The town is situated mostly on an alluvial plain at the foothills of the mountain Bing61, with a small tributary of the ~arbuhur river flowing through it. Nearly 98 per cent of the houses in Varto, M1 of them adobe construction like those shown

VA~TO REGIONAL SCHOOL

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in Figures 13 and 14, were destroyed. The shock killed 18 per cent and wounded 24 per cent of its inhabitants.

Figure 15 shows one of the few modern structures in Varto that was heavily damaged. It is a two-story brick house situated at the entrance to Varto, on the Hmls road. The house, which was still under construction at the time the earthquake occurred, is founded on very soft ground with high water table and is situated next to a spring which is shown on the right corner of Figure 15. The masonry of the first floor was heavily fractured and it was dislodged with much of the interior walls having been damaged beyond repair. In contrast, the basement suffered very little damage. A close inspection of the interior walls showed that the damage was caused by large horizontal displacements of the heavy tie-beams and

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reinforced concrete flat roof with respect to the hollow cement brick walls. Some of the partition walls had disintegrated and unbonded corners had opened up. The hollow bricks were very heavy. They were made with a very poor cement paste and had cavities which varied in shape and size.

VARTO REGIONAL SCHOOL

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FIG. 18. Recreation Hall. Mode of collapse of reinforced concrete frames.

FIG. 19. Varto Regional School. Recreation Hall destroyed.

A regional school, similar to that inspected in Hires is situated on the north-east edge of the town. A plan is shown in Figure 16. The guest-house, the rest rooms, class-rooms, the ten bungalows, the pump house, and part of the restaurant were one-story brick structures with lightly reinforced concrete tie-beams and roof slabs covered with corrugated iron pitched roots. The two dormitories, the resi-

68 BULLET1N OF THE SEISMOLOGICAL SOCIETY OF AMERICA

dence halls and the hospital were two-story brick structures. Some of t h e m had a masonry basement covered with reinforced concrete slabs cast in situ and supported by wall beams. The recreation hall and the pump house were reinforced concrete frame structures; the former of eleven frames spanning a hall 13 meters wide.

The site is comparatively flat and the various buildings were constructed on thick alluvium. The plant and the south end of the residence halls were founded on terraced ground made of recent fill material. The class rooms and the restaurant were built on natural terrace cut at its west and south ends. Other structures

FIG. 20. Var to Regional School. Remains of Recrea t ion Hal l viewed from N.E. Detai l A shown in Figure 21; B in 22; C mezzanine.

(Bungalows No. 1 to 10) were founded on natural terrace, four to five meters above the low-lying ground on which the two dormitories, the hospital and the recreation hall were built, where the water table is very near the ground surface. At the time of our visit it had risen above the 1.5 meter contour and had flooded most of the site. The effects of the earthquake on these structures were most dra- matic and are shown in Figure 17.

The recreation hall was a one-story reinforced concrete frame structure having moment resistant joints. The entire structure was separated into two parts by a structural joint. The southern part is 30.5 meters by 13.5 meters in plan and the northern part 30.5 meters by 5.5 meters in plan. The northern part was composed of eleven frames spanning 13 meters across the hall, and 6.8 meters high in the middle, and of three roof beams extending its full length supporting a reinforced con-

VARTO iTSTI)KRAI~I EARTHQUAKE OF 19 AUGUST 1966 69

crete pitched roof. The southern part of the structure was a hybrid construction which was supported partly by reinforced concrete columns and partly by a brick wall with a heavy longitudinal beam supporting the roof slab (see Figure 18). The columns extended through a perimetric beam, cast at floor level, running the whole length of the structure. According to information obtained locally, this structure had been designed to resist lateral earthquake forces.

FIG. 21. Varto Regional School. Detail A of Figure 20.

The total collapse of this structure is evident from the remains shown in Fig- ures 17 and 19. Some indications of the basic structural and construction weak- nesses which led to this collapse may be noted in other views of the remains of this hall. From Figure 19 it can be seen that the northern part of the hall collapsed to the north and the frames collapsed to the south. Figure 20 shews the separation of the two parts of the structure along their joint. This exposed a number of interesting details which by themselves are sufficient to explain the behaviour of the structure. The eleven columns of the frames facing north collapsed yielding systematically


in three points along their height; i.e., points A, B, and C of Figure 18 which are shown in Figures 21, 22 and 23 respectively. These points corresponded to the base of the columns, where they supported a cantilevering mezzanine and at their connection with the cross-beam at the top. At points A, B and C very little concrete got through the closely spaced reinforcing bars to bond them (Figures 22

FIG. 22. Varto Regional School. Detail B of Figure 20; joint partially filled with poorly cemented aggregates.

and 24). Some of these points were found to contain aggregate up to 8 centimeters in diameter with practically no cement paste, as shown in Figures 24 and 25. The southern side of the frame collapsed by folding up as shown in Figures 18 and 26. I t seems that the shock caused some instability in the frame which forced its footing H to move inwards to a position H'. As a result of this movement, which had very little resistance from the frame, the rest of the structure folded up in a position as shown in Figure 18, i.e., H ' - G ' - F ' - E ' - C ' - B ' - A . * Due to the inward

* Moinfar (1967) suggests that the cause of collapse was due to insufficient tie beams in the longitudinal direction.

VARTO "0STUKRAN EARTHQUAKE OF 19 AUGUST 1966 71

thrust of the footing H, the floor of the hall had heaved up to 50 centimeters in the middle (H'-E'-A) throwing up the parquet floor with its concrete base, which was shattered. A long fissure in the ground running two meters south of point G' was found to extend along the full length of the structure. This should be a tension crack formed by the movement.

FIG. 23. Varto Regional School. Recreation Hall viewed fromW; details A and B shown in Figures 24 and 25 respectively.

Another reinforced concrete skeleton structure was the heating plant, the remains of which are shown in Figure 27. The main framing consisted of transverse reinforced concrete frames each with four columns except in the stairwell where the frames were interrupted and the ends of the beams were supported by hollow brick walls. A 21-meter high chimney of reinforced brick work was attached to the foundations of the structure but it was separated by a structural joint from the main construction. The plant collapsed completely but the chimney was left standing with absolutely no damage. Some indications of the structural weakness

72 B U L L E T I N OF T H E S E I S M O L O G I C A L S O C I E T Y O F A M E R I C A

which led to this collapse may be noted in the shattered remains. The beams of the first floor with the combined action of the wMls which they supported were far stronger than the supporting columns. The columns, on the other hand, having been designed to resist lateral forces, had such a large ratio of area of steel reinforcement to area of concrete that where they joined the beams there was no space

FIG. 24. Close-up of detail A of previous plate; large aggregates poorly cemented.

for the coarse aggregate of the concrete to go through and bond the reinforcement; most of the joints between colurmls and beams were very poorly bonded. Close inspection of the contact surface between the chimney and the plant showed no signs of pounding, nor was there any damage to the chimney. Although the ground on the west side of the plant was soaked with ground water, no cracks or fissures were observed in the vicinity of the plant.

One of the most spectacular failures was that of the two residence haJls which were located at the entrance of the school. They were identical wall bearing two- story structures founded on strip footings, with ~ large number of openings and a

VARTO TJ-STiJKRAN :EARTHQUAKE OF 19 AUGUST 1966 73

heavy external tie-beam supported by the brick panels between the windows. Figure 28 shows the ruins of the two halls with the standing portion of the refectory on the right. Figure 29 shows a close-up of the stacked floor slabs of hM1 No. 2. With the exception of a relative settlement of the foundations with respect to the concrete sidewalk, no ground deformations or cracks in the ground were found near the ruins.

]:IG. 25. Detail B Figure 23; closely spaced reinforcing bars unbonded to the rest of column.

7 4 BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA

The dormitory No. 1 was a two-story wall bearing structure of irregular plan, divided into two parts by structural joints. The external walls were tied together with a lightly reinforced heavy concrete beam (0.5 X 0.5 m.) on which the floor slabs are cast. The tie-beams and spreaders of the internal walls formed a massive construction which rested on hollow brick walls of very low quality laid in lime mortar. The beams of the external walls were supported by brick columns or brick panels between windows and the stairwell by four slender concrete columns. Figure 30 shows this structure after the earthquake. The north wing collapsed while the

. . . . . . . . . . . i//i/¸:¸/ 41 i i!! i i iiil

FIG. 26. Varto Regional School; folded columns of recreation hall viewed from the southeast; arrows show improper reinforcing.

rest of the structure is left standing on the verge of collapse. Figure 31 shows a closer view of the part which is still standing, showing the masonry walls of the ground floor which suffered little damage and the hollow brick walls of the first floor which spread out. Of particular interest in this view is the lack of bonding of the brick-work at the corners of the walls. The interior of the ground floor of the south wing was badly damaged.

Dormitory No. 2, of similar construction, collapsed completely leaving the floor slabs piled on one another. The details of the failure of this structure were some- what different, in that the east wing settled about 30 centimeters into its foundation, but the basic mechanism was similar. This settlement is shown in Figure 32 and it might have extended diagonally through the foundation if the fissures in the ground found in the southwest side of the building are at all connected with ground deformations that have been observed in this part of the site. The shear failure of the basement wall along the window panels is of interest. As the sguth east corner

VARTO ~.JSTUKRAN :EARTHQUAKE OF 19 AUGUST 1966 75

of the structure settled into the ground, the internal walls carried all the load of the upper-structure. The crushing of the brick walls in the basement and the punch- ing of the foundations into the ground suggest this. At the far end of the south wing of this building the foundation slab was bent and fractured with a heave in

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FIG. 27. Varto Regional School; collapsed central heating plant.

FIG. 28. Varto Regional School viewed from W; collapsed residence halls, floor slabs piled one on another; chimney and pump-house, Figure 33 standing (right). Note boggy foreground.

76 B U L L E T I N O F T H E S E I S M O L O G I C A L S O C I E T Y OF A M E R I C A

F I G . 29. V a r t o R e g i o n a l S c h o o l ; r u i n s o f R e s i d e n c e H a l l 2.

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F I G . 30. V a r t o R e g i o n a l S c h o o l ; r u i n s o f h o s p i t a l (A) a n d D o r m i t o r y 1. N o t e t h e s t a c k of s u c c e s s i v e f l o o r s l a b s .


the middle about 40 centimeters. This heaving of the foundation was similar to that observed in the recreation hall.

The ultimate cause of the total collapse of the hospital building was not possible to establish. Some indication of a differential vertical movement of the foundations was found and numerous fissures clustered around the south corner of the building.

The refectory was a one-story brick structure built in two parts which were connected by a brick-walled corridor. The east wing had on either side a large number of openings and part of it was founded on a fill about 80 centimeters high. Because of the large number of openings, an excessively thick tie-beam was used

FIG. 31. Close up of Dormitory 1 showing unbonded corner (arrow).

running on the external wall supported by brick columns. The south part of the east wing collapsed, according to an eye-witness, a few minutes after the earthquake, pulling down the rest of the wing. The west part of this structure suffered very little damage. As can be seen in Figure 17 even the brick chimney was left standing. There was no indication of pounding between the two wings, but fissures in the ground near the edge of the ramp shown in Figure 16 were found.

At the edge of the school grounds, a small structure, which housed the electric plant and a pump, was found to be severely damaged. Figure 33 shows this structure, with its walls spreading out but still standing. I t was built of badly baked kiln bricks laid in lime mortar, resting on a mat foundation (?) on soft ground. The walls were tied together with a heavy beam running along the external walls. An inspection of this structure showed that the horizontal movements during the earthquake should have been rather small. The exhaust of the diesel engine with


FIG. 32. Var to Regional School; ruins of Dormi tory No. 2; note se t t l ement in the middle [ ] _ ~ _ ~ _ ~ ~ ~ and sheared window panels of ground floor.

FIG. 33. Var to Regional School; electric p lan t ; note heavy ring beam and unbonded brickwork of r ight corner (arrow).

VARTO UST'UKRAN :EARTHQUAKE OF 19 AUGUST 1966 79

FIG. 34. Varto Regional School; class-rooms slightly damaged.

FIG. 35. Interior of class rooms.

its silencer emerging from a window of the structure was left standing. The ground around this house was very wet, but no cracks in the ground were noticed.

The class rooms were housed in a long one-story construction built with hollow bricks. The tie-beams and cast in situ concrete roof slab were supported by the


walls and by slender concrete and brick columns. This structure shown in Figure 34 performed rather well. There was little damage to be seen from the outside, but irregular cracks in the plaster of the partition walls and the fracture of some columns inside showed some signs of distress (Figure 35). Most of the window panes were not broken and the doors and windows functioned properly.

The ten bungalows shown in Figure 36 with the class rooms in the foreground performed very well. These are wall bearing constructions with comparatively light~ tie-beams and concrete false ceilings covered with corrugated iron sheets. This group of houses is situated on the highest ground of the site (see Figure 16) and is founded on unreinforced concrete mats (?). The damage consisted mainly of minor cracks in the plaster of the walls along the contact of the tie-beams. Bunga-

H / / ~ :-~ :/H::"~::H :,i

FI~. 36. Var to Regional School; view of class rooms and bungalows. Only Bungalow No. 1 (A) damaged.

low No. 1, however, was an exception; one of its walls collapsed together with its brick chimneys. The only difference between this and the other bungalows is that No. 1 had a rather complicated plan and that its tie-beams did not completely encircle the outside walls.

Neighbouring the Varto School to the west was a compound of five houses, recently built of brick with heavy ring-beams and cast in situ roof slabs. One of them was built of stone masonry and it was founded on a concrete mat. The site was a low-lying field, about one meter below the zero contour shown in Figure 16, and at time of our visit most of it was saturated. The ground water had risen above the surface of the ground (see foreground, Figure 28). Figure 37 shows the remains of one of these houses; four more collapsed in a similar manner. A series of small noncontinuous ground cracks passed in a north-northwest direction about one meter from the ruins sho~m in Figure 37. A common feature of the collapse of these


FIG. 37. Varto. Ruins of masonry cons t ruc t ion on boggy ground next to Var to Regional School; arrows show ground crack.

FIG. 38. I4arkarut . Ruins of the regional infirmary.


five houses was that their outside walls had been thrown outwards and no direction of collapse could be established.

There is a remarkable correlation here as well as in the Varto School between the location of the structures tha t collapsed and the area that was saturated by the ground water table, which from Figure 16 was just above the contour of -~-2 meters. This area was seasonally flooded and some of the structures built there were founded on artificially raised ground. The southern part of the paved courtyard between the class-rooms and the dormitory (No. 2), which was built on slightly raised ground, was found to have sunk irregularly in places. Although the cause of this is not known, it is probably associated with the high-water table.

The part of Varto that is built on comparatively high ground, such as north of the bazaar, on the ma'm road, was little damaged. From a group of brick houses with pitched corrugated iron roofs, about a dozen of them suffered only some cracks in their plaster. The roofs of two of these houses can be seen on the back- ground of Figure 13. This lack of serious damage is rather surprising as these houses are only one hundred meters from Varto's center and less from the bank, a reinforced concrete skeleton building that was damaged beyond repair. Quite a few lightly damaged houses were also found on the road to ~stiikran (~aylar). East of Varto, on the way to Karhova via t~stiikran, the village of Karkarut (Sazlica) was totally destroyed. This village had over 50 per cent of its houses destroyed or damaged beyond repair by the earthquake of March 7th.The regional health center however, was built after that earthquake on the hill overlooking the village. Figure 38 shows the ruins of this construction. Part of it sank into the ground. Numerous fissures in the ground indicated that the east portion of the structure was on a small incipient shde.

Further west, at Leylek, the destruction was also complete. The village was severely damaged by the March earthquake, losing 25 out of its 59 houses, and the August shock completed the destruction. Here many of the houses were built of river boulders and gravel, which was laid in clay mortar.

Near Sofian (Do~anca), more houses could be seen standing. Some were of dry rubble construction with heavy earth roofs.

At Ustiikran, a village of about 500 inhabitants, the damage to the local houses was heavy. This village had already lost 50 per cent of its houses by the March earthquake. The shock of August 19th killed about 12 per cent of its inhabitants and destroyed or damaged beyond repair all the houses including the local school which was of similar construction to that in Karkarut. Four one-story brick houses built at the entrance of the village, similar in size and in construction to the bungalows of the Varto school, had their chimneys thrown down but otherwise were not excessively damaged.

To the south and west of tJstiikran the villages of Cahlek, I-Iamtik (Kii~iiktcpe), and up to Kaslman (K6priiciik) on the north flanks of the Kar-bo~an mountain, were totally destroyed. On the southwest slopes of the Kanbo~an the damage seems to have been serious but definitely less severe. The villages of Bazikan (Kayanarca), Dodan (Ilbey), I~ale~ik (Aydmpmar) and Zorabet were heavily damaged but no distinction could be made between destruction and heavy damage.

South of ¥arto, on the way to Mus, the damage was found to decrease rapidly with distance from Varto, but rather erratically. This was mainly due to the fact

VARTO t~STt~KRAN EARTHQUAKE OF 19 AVGVST 1966 83

that this part of the epicentral region had already been damaged by the shocks of March 7th and July 12th. The village of Harabeyyakup (Tasdibek) and the twin settlements of Alag6z were totally destroyed. Tepek6y, the center of the July 12th earthquake, was a large village on the west bank of the ~arbuhur I~iver, and was also destroyed, with the exception of a few brick houses at the south end of the new part of the village which were heavily damaged but did not collapse. At this place, a large slide triggered by the August earthquake had blocked the main road and ruined a few repaired houses.

About 30 kilometers south of Varto, Mercimekkale (Sakavi), a village of about 900 inhabitants on the south bank of the Murat River, was severely damaged and

:FIG. 39. Mereimekkale . Ruins of local school. Note heavy ring beam arrows.

about one quarter of its adobe houses collapsed killing 15 persons. The damage here was definitely less than in the northern parts of Sakavi. In the village the local school, a field-stone construction with an enormous tie-beam of reinforced concrete, 50 by 60 centimeters thick, collapsed. Figure 39 shouts that these tie- beams were not connected at the four corners of the structure; and that they were thrown out by the shock and carried the masonry walls with them.

South of Mereimekkale, the damage decreased very rapidly. At Klrevi (Senova) and near Akgan (Tasoluk) more than 60 per cent of the adobe houses were not damaged, and after crossing the River Murat on the way to 3/Iu~, very little seri- ouse damage could be seen.

The Agricultural School at Arparslan, a modern complex of brick houses, one- to three-story high, showed practically no damage. Hair cracks in the plaster and a few minor cracks between partition walls and columns was all that could be seen.

The damage in Mu~, the capital of the province, was negligible. Cracks in the

84 BULLET1N OF THE SEISMOLOGICAL SOCIETY OF AMERICA

plaster and some dislodged partition walls in three-story reinforced concrete structures was noticed. Some very old local type of construction did collapse, but these were few and rather ruined already by lack of repairs.

North of the Murat River, in the district of Ziyaret (Mid,i) the villages of the plains around Ahino (Karde~sler) and Evran (Ya~eflar) were seriously damaged. From local information, however, it seems that this damage represents the cumula-

Fig. 40. Bridge on the River Murat, looking south, towards Mus.

rive effects of the shocks prior to August, which was augmented by the Varto earthquake.

ENGINEERING STRUCTURES

There are no important engineering structures in the region. The bridge of the River BingS1, a reinforced concrete structure about 15 kilometers south of Varto, suffered absolutely no damage. The BingS1 Cayi bridge slid bodily on its pedestals a few centimeters to the east allowing its expansion joints to open up.

Figure 40 shows the bridge on the River Murat. Local information suggests that this bridge had its superstructure rebuilt a number of times in the past. This ap-

VARTO "U-STUKRAN EARTHQUAKE OF 19 AUGUST 1966 85

pears to be true when one looks at the axis of the bridge from a distance, as shown in Figure 40. There is no evidence that this bridge suffered any damage by the August shock.

A regional school, similar to those in Hmls and Varto, was built at Solhan, about 50 kilometers southeast of Varto. According to reports it suffered no damage.

THE EFFECT OF THE BUILDING CONDITIONS ON DAMAGE

Houses in the epicentral area can be divided according to their type of construction into four broad categories: traditional Anatolian adobe houses with or without timber bracing, hewn masonry houses, hollow cement or kiln-brick houses, and houses of reinforced concrete construction.

In structures of the first and second category the roof is usually supported by timber beams and it is covered with a thick layer of tamped earth. Brick constructions usually have heavy reinforced concrete tie-beams running on the exterior walls, on which the roof slab is cast in situ in lightly reinforced concrete. This is then covered by a pitched roof of corrugated iron sheets supported by wooden frames.

In a few modern houses in the Varto region the standards of planning and the accommodation provided is good. The construction details, such as wall thickness and reinforced concrete members are heavy, but nevertheless comply with accepta- ble requirements for seismic regions, for which most modern public buildings are designed.

The quality of the brick work varies tremendously from site to site and from one part of a structure to another. The mortar is made mostly of lime and is of very poor quality. The joint between bricks is usually not completely filled. Where hollow cement bricks are used the mortar does not adhere to the bricks, nor is the brickwork bonded at the corners.

The standard of workmanship with non-traditional building materials such as concrete and reinforced brick-work is far below the standard of design. In reinforced concrete work the aggregates are very dirty and badly graded. Figures 22, 24, and 25 show samples of the quality of concrete found in skeleton structures that collapsed. Aggregates up to 10 centimeters in diameter were found in beams and columns. The concrete is usually excessively porous and contains embedded debris and loose or uncemented aggregates. The latter case is common in column-girder junctions were the space between reinforcing bars is too small to allow the coarse aggregates and cement paste to pass through and bond the bars.

Loose aggregates and embedded debris in structural reinforced concrete members was found to be due to improper mixing and also due to the mixing of the concrete with shovels directly on the ground, in reinforced concrete work the steel was too near the surface, and there were not enough stirrups or cross-binding. Insufficient or badly positioned continuity bars at joints are common features. As a result the reinforced concrete frames were weaker than they need be.

GROUND MOVEMENTS

From interviews with the local people it appears that the main shock was of a very brief duration. In Varto the shock seems to have lasted between 3 and 5


seconds. I t was preceded by a thundering noise resembling artillery, coming from no specific direction. The ground movements were initially horizontal, directed to the southeast, followed by a series of strong vertical joJts. An employee at the Varto Regional School was in the basement of the plant at the time. He felt the horizontal movement which nearly threw him off balance and immediately the vertical shocks which brought down the plant on top of him. On the road between Varto and Tepek6y a loaded truck overturned as the driver lost control of his vehicle and many parked cars and lorries in Varto moved on locked wheels. Many people found it difficult to walk but we did not hear of anyone thrown down. Pack animals panicked but did not fall down. Observers agree that throughout the epicentr~l region it was the second shock, that of the vertical movement, that caused the greatest damage.

The duration and character of the shock varied with the distance from Varto. At Hmls it lasted about 5 seconds but the horizontal movement seems to have been predominant over the vertical. Similarly in Mug, the horizontal movements were felt very strongly, while information about the importance of the vertical motion of the ground is conflicting.

INTENSITY DISTaIBVTION

In an economically developing rural area such as East Anatolia the assessment of the intensity after an earthquake poses special problems since many of the criteri~ needed for the grading of the intensity are partly or totally lacking. The are~ affected by the Varto-t)sttikran earthquake is sparsely populated and with very few exceptions all houses are of adobe brick or mud-wall construction. There are very few well built houses and even fewer types of other construction that could serve as a measure in assessing intensities. Moreover, many of the villages in the epieentral area had been already damaged or partly destroyed by the earthquakes of March 6th and July 12th. Thus, it was not possible to assess what effects the earthquake of August 19th alone had on more than 50 per cent of the settlements, except by interviewing the local people. Another difficulty was posed by the pe- culiar circumstances of modern reinforced concrete constructions which were designed to resist earthquake forces and which were so poorly built that they suffered more damage than the local adobe construction.

If we had in the epicentral region a variety of damaged structures built according to some standards, the assessment of intensity, using one of the available intensity scales, would be straightforward. Here the only structure which could serve as guide to the intensity was the village cistern; a brick masonry structure, clad with hewn stone. One of them is shown in Figure 41. In some cases, standard brick one- story bungalows built by the ministries of Education and Public Works, such as those shown in Plate 28, were also used.

As in the case of the Buyin-Zahra earthquake of September, 1962 in Iran (Am- braseys, 1963) where properly built or standard structures were found side by side with adobe constructions damaged by the earthquake, it was possible to see that an intensity not greater than VII (MM) was sul~.cient to damage beyond repair, while an intensity V I I + caused total collapse of the typical adobe houses.

Thus, from the behaviour of the local houses ~lone we could not determine


intensities greater than VII-~ (MiVI). There were very few other types of construction whose damage due to vibrational effects would help to assess intensities greater than VI I+ . Moreover, the weakening of many of these structures by the shocks of March and July made our determination of the intensities even more doubtful. The value of fissures and of landslides as items that help to determine higher intensities were found to be questionable, and such effects were dismissed as evidence of high intensity.

Therefore, the assessment of intensity distribution in the Varto area from per- sonal observations led to subjective interpretations. As in the Buyin-Zahra earth-

FIG. 41. ~stiikran. Village cistern undamaged.

quake of September, 1962 in Iran, and more recently with the earthquakes of March 31st and July 6th, 1965, (Ambraseys, 1967) in Greece, the Modified Mercalli scale was found to be inadequate, it allows, however, enough flexibility for the observer to use his own judgment and arrive at homogeneous assessments of the intensity. In contrast, the use of the proposed Medvedev-Sponheuer-Karnik scale (Medvedev et al., 1965) was found to be impracticable. This scale makes an effort to distinguish the effects of earthquakes between structures of different resistance. Its ratings are so rigidly defined for test material which is in reality so variable that the very basis of this scale becomes untenable.

Using our own observations and the information supplied to us by the local


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VARTO "USTUKRA:N" EARTHQUAKE OF 19 AUGUST 1966 89

authorities ~-e concluded that the maximum intensity in the epicentral region, based on purely vibrational or shock effects, should have not exceeded IX (MM).* We can only assume that if it did, we must have missed its effects. Effects which have been used by some observers to assess maximum intensities of X or even XI (MM), solely on the fact that the concrete structures of the Varto Regional School had collapsed so dramatically, or on the huge landslide at TepekSy, we con- sider to be misinterpretation of the scale.

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There can be no doubt that the intensity in the town of Varto was not the maximum. i t did vary within short distances by as much as one to two degrees, but on the average it was comparatively lower than in other places further northwest. In ¥arto, only one of the three cisterns was slightly damaged. Many well built brick houses withstood the shock despite their being weakened by the previous shocks and in spite of the bad foundation conditions. Nowhere in the north and northwest part of Varto was total collapse noticed, and as mentioned previously north of the bazaar road quite a few adobe houses with timber bracing were damaged, but far from seriously.

* 0zocak (1966) gives a maximum intensity of VIII (MM).

90 :BULLETIN OF TI-IE S EIS M OLOGICAL SOCIETY OF AMERICA

Figure 42 shows the distribution of damage within the epicentral region. This, of course, includes the damage caused by the two shocks prior to August 19th, and it includes also the effects of the stronger aftershocks. Dots or circles show the location of all villages and settlements in the region; hence their distribution shows the density of habitation of the region. For instance, north of the Karhova-Varto axis the blank space represents the Bing61 mountains which are totally uninhabited, while the blank space between G6nyk-Solhan and Karhova-Varto shows the Serafettin mountains which rise up to 2,500 meters.

Figure 43 shows the intensity distribution in the detail warranted by the available data. Within the central contour, intensities should have been greater than VlII but should not have exceeded IX (MM). Within this zone it was neither possible to isolate specific regions of the same intensity nor to assess beyond doubt the maximum intensity based on vibrational effects. Localities that showed intensities approaching IX are shown, together with the locations where ground effects were found.

The map shown in Figure 43 was prepared from a variety of sources of information and the intensity was assessed in a way similar to that used for the Buyin- Zahra earthquake in iran (Ambraseys, 1963, p. 734). First, we studied reports from investigators of the Ministry of Rehabilitation who visited the areas of damage after the earthquake. These reports were supplemented by detailed lists of damage for over 500 villages which are kept at the Resident Engineers' Office in Erzurum and Mus. These lists give for each village the number of houses and the number of inhabitants and also the number of houses that were destroyed, damaged beyond repair, or damaged by the shock, together with the number of people killed or injured by the earthquake. Other lists refer to the damage or lack of damage to special types of construction such as schools, health centers, and other public buildings. Newspaper clippings from the local and the national press were also consulted. From these sources, the percentage of damaged and destroyed houses to the total number of houses (damage ratio) for each village was calculated. Then, the authors visited about 25 per cent of the villages in the area of greatest damage and assessed independently local intensities using the (MM) scale. These intensities were then correlated with the corresponding damage ratio whose characteristics and distribution are given in Figure 42.

Maximum intensities were found along the Varto-~sttikran axis on the foothills of the Bing61 mountain. The general trend of the epicentral zone was northwest- southeast with a marked decrease in intensity southwest of this axis. To the northeast, the intensity zoning is uncertain because of the lack of villages and the inac- cessibility of the Bing61 mountains.

Towards the south-east end of the Karhova-Varto axis, a few kilometers from Varto, the intensity distribution of the August 19, 1966 shock becomes confused in regions that had been affected by previous shocks. An unmodified use of the cumulative effects of the seismic activity since March 1966 will result in producing isoseismals which will widen in a north-northeast and south-southwest direction giving a "pear-shaped" isoseismal configuration with its widest zone stretching between Hires and Tepek5y.

The isoseismal map shown in Figure 43 was necessarily constructed on the basis of the cumulative effects of the earthquakes of March, July and August,

VARTO i~STUKRAN EARTHQUAKE OF 19 AUGUST 1966 91

1966 and it should, therefore, be interpreted as a rough approximation to the real intensity distribution due to the earthquake of August 19th alone. This difficulty of the assessment of intensity of earthquakes from their cumulative effects lies obviously on the structure of the intensity scale itself which is not based on instrumental data. Intensity ratings in the epicentral area of a strong earthquake are deduced mainly from the damage caused to variot~s structures. But with cumulative effects, this damage is the result of more than one earthquake and since it is not known how much or how little previous earthquakes have weakened these structures, the assessment of intensity becomes practically impossible.

FIo. 44. Dirik. Trail of boulder dislodged from outcrop.

GROUND EFFECTS

Ground ruptures, distortions and fractures in the ground were developed very widely in the region, while few features were found to be associated with a fault zone. Ground ruptures, in general, appear with greater frequency and prominence within the epicentral region, but incipient and fully developed landslides, though of different size, appear throughout the whole region between Mus, and BingS1, Hmls and Erzurum. Rockfalls and shattering of exposed volcanic columnar forma- tions, such as shown in Figures 6 and 44, occurred during the March 6th earthquake and also during the main shock of August 19th.

Having practically no idea of the ground effects caused by the shocks prior to August 19th, it was difficult to assess ground effects that can be safely attributed solely to the Varto-Ustiikran earthquake and to its aftershocks. Nor was it possible to distinguish between those: slides that have been causing considerable concern in the past years and those that should be associated specifically with the main shock. According to the Highway Department, prior to the main shock the epicentral regions and also more distant regions in marls showed many incipient slides


of various sizes that were causing some damage every year to the main and secondary roads in the district. Figure 45 shows a slide that has been going on for a long time, over 80 kilometers away from the epicentral area.

Our observations, therefore, contain such features that may very well have existed before the earthquake and which were only aggravated and augmented in size by the earthquake. Consequently, their existence at a particular place should not necessarily be interpreted to mean high intensities.

RockfMls of various dimensions were found mostly along the road from IIarabeyakkup to TepekSy and south of this place. They were also found in the valley of Leylak and northwest of ~stiikran and south and west of Hmls. Boulders up to two meters in diameter were dislodged from steep slopes. Some hopped and

FIG. 45. L o c a t i o n 78 K i l o m e t e r s f r o m V a r t o on t h e w a y to E r z u r u m . Slide on w e a t h e r e d m a r l s .

skipped down slope for several hundreds of meters, gouging the ground surface and leaving a very characteristic trail. Figure 44 shows an outcropping mass of volcanic rocks a few kilometers south of Dirik (Yficetepe) which was shuttered by the main shock and a boulder which rolled down the slope.

Many minor slides in the epicentral region were connected with springs, pre- existing or associated with the earthquake. Figure 46 shows one of the new springs near Zilokomu, presumably associated with the earthquake of March. On steep slopes, such as those of the Leylek valley shown in Figure 47 shallow slides extending over large areas were common. The most damaging landslide was that triggered by the shock near TepekSy. Figures 48 and 49 show the central part of this half million cubic-meters landslide with the ruins of old TepekSy and the river ~arbuhur at the back. The slide blocked the ~[us-Erzurum road along a length of about 160 meters shifting the highway pavement many tens of meters and lifting it up about 4 meters.

SURFACE EVIDENCE OF FAULTING

A careful, but not exhaustive, search within the epicentrM region did not disclose any clear-cut trace of recent continuous faulting, but suggestive evidence of discontinuous faulting was found Mong a length of over 30 kilometers.


FIG. 46. A~gelin. Incipient slide NW of A~gelin and spring caused by the earthquake of August 19.

FIG. 47. Leylek. Scarps of slides on Turtle's ravine; some of these scarps merged with secondary fault features (arrows).

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FIG. 49. TepekSy. Part of the slide at TepekSy looking north.

FIG. 50. North of Varto. Secondary fault trace bearing N 35°E (dextral).

96 BIJLLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA

Secondary features suggest that there must have been a structural re-adjustment along the Karhova-TepekSy axis. Unlike the strike or dip-slip ruptures along other parts of the North Anatolian fault, the Varto earthquake produced a complex pattern of short ruptures within a zone about 5 kilometers wide and 30 kilometers long. The ruptures have quite different trends and the displacements that

FIO. 51. Nor th of Varto. Secondary fault trace bearing N 125°E (dextral).

they caused are in different directions. A number of long en echelon fissures, some- times merge with cracks produced by slides, making differentiation of the purely structural effects very difficult.

In what follows we describe a number of instances where the observed surface effects seem to be connected with features of secondary faulting. The types of rupturing that we observed vary greatly and there is always some doubt as to whether these all represent actual tectonic fault movements or gravitational movements which resulted from the earthquake.

About 3 kilometers from Varto on the main highway to Hmls the road surface

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98 B U L L E T I N OF T H E SEISMOLOGICAL SOCIETY OF A M E R I C A

is intersected by a transverse crack a few centimeters wide. The alignment of the tension and compression cracks on either side of the road shows dextral movements for a length of about 300 meters with the downthrown side to the east-northeast. Figure 50 shows part of the trace of the cracks arranged en echelon, bearing N 35°-E. Here the ground is comparatively flat, but the south end of the trace turns around to follow the strike of a small hill and develops into a minor slide with a spring situated beneath it. The northern portion of the trace dies out after it has traversed a mild slope at right angles to its strike. I t is probable that this trace is connected with one of the two marginal sides of a slide, the other side being too weak to notice.

FIQ. 53. East of Harabeyakkup. Ground deformation bearing N45°E caused by slumping.

A similar trace of en echelon cracks, about 200 meters long was found just off the main road, two kilometers north-northwest of Varto. Again the movement was dextral, with an axis bearing N 125°-E. Here the ground was absolutely fiat with a total absence of any indication of gravity movements. More evidence of a whole family of tension cracks and pressure ridges of comparatively shorter lengths, was found about 1.5 kilometers north-northeast of Varto, Figure 51. These fractures did not form scarplets except in irregular topography, in which the scarplets faced either direction depending on the direction of the slope, and always indicated dextral displacement; the axis of these fractures was bearing N 115°-E.

About one kilometer south-east of Dirik, an alignment of scarplets was found to trend roughly N 135°-E following a course at 45 ° to the strike of the hill, for a length of about 200 meters after which they formed a continuous scarp of small dextral displacement with a 'small throw to the southeast. Figure 52 shows part of the trace, which could not be followed for more than another 300 meters.


Past Harabeyakkup on the way to Mus, another series of cracks bearing N 45°-E was found on comparatively flat but soft alluvium, Figure 53. These cracks could be traced for about 250 meters. I t seems that they were produced by lurch- ing of the water-soaked alluvium.

Northwest and east-northeast of Varto there was a large number of fissures. Some of them were aligned en echelon for a few tens or hundreds of meters, particularly in the Leylek area and north of Ziyaret Tepe. They extended discontinuously all the way to Hamuk and Usttikran showing dextral displacements and on the average bearing N 290°-E. Most of these features, however, were connected with sloping ground with NW-SE strike suggesting cracks formed by landslides rather than by tectonic movements. Figure 54 shows a fracture trending N 10°-E for a

FIG. 54. Hamuk. Secondary fault trace bearing N 10°E (dextral).

few hundred meters up the hill and over it with compression ridges showing a dextral movement. This is perhaps one of the few cases where gravity effects can safely be excluded.

On the southern portion of the Bing61 mountain, near Mostan, large fractures developed along the base of the hills north of Saman and again at Rakasan in the foothills to the east. All these fractures were vertical or steep and produced south- facing scarplets shattering the basaltic rocks. North of Taseimany small east-west trending cracks formed in disintegrated volcanic rocks for about 300 meters. These appear to be fractures along jointing with no movement indicated.

Perhaps the information concerning long fractures supplied to the writers by the local authorities in places which were not visited should be added. Some fissuring along the line Kale~ik-Kainajha (Karahamza) seems to be relevant, with intense displacements between Bazikan and Kolan. Also a fracture through marls near Abdalankomii extending a few hundred meters was mentioned.


CONCLUSIONS

We may conclude with some general remarks: (1) The ¥arto-~sttikran earthquake of August 19th was preceded and followed

by considerable seismic activity with strong shocks and heavy damage within an area of 4,000 square kilometers. This area has been quiescent for over twenty years, but otherwise it is well known for its seismic activity.

(2) Once more it was found that adobe houses and other types of local construction have widely different resistance to earthquake forces, but that an intensity of about V I I + (MM) will cause such heavy damage to these types of construction that no distinction can be made between heavy damage and complete destruction. Consequently, from the behaviour of the local houses alone, intensities greater than V I I + (MM) cannot be assessed.

(3) The strong shocks that preceded the earthquake of August 19th made it practically impossible to assess the intensity distribution caused by this earthquake. This, once more, brings out the inadequacy of existing intensity scales and the intrinsic limitations of intensity assessment. Obviously more research is needed using strong motion recordings rather than improvement of the existing (MNI) scale. The fact that we are not yet in a position to be completely rigorous in our definitions of various intensity ratings makes any changes in a well-established, though palpably unsatisfactory, intensity scale unwarranted. The writers have come to the conclusion that the assessment of intensity in developing countries has systematically been over-estimated in the past. I t is not only that mud, adobe stone and similar heavy masonry cease to be a measure for assessing intensities greater than V I I + (MM), but also that ground effects such as slides and slumping of fills which occur under normal conditions are not necessarily indicators of high intensity. Moreover, the damage or lack of damage to engineering structures and to structurally complicated construction cannot be adequately described and interpreted by seismologists, geologists or geophysicists alone, regardless how com- petent they are in their respective fields.

(4) l~einforced concrete structures, some of which are reported to have been designed to resist earthquake forces, failed completely due to improper construe- tion and poor building materials, while nearby houses of local construction suffered only some damage. This illuminates the need for better methods of construction and the use of better materials rather than for advancements in design, particularly in developing countries. The behaviour of these structures points to the need for supervision during construction and for training of the local builder in the proper use of building materials rather than for more advanced codes and regulations.

(5) A careful but not exhaustive search in the epieentral region did not disclose any trace of continuous faulting. A complex pattern of ground ruptures within a zone about 5 kilometers wide and 30 kilometers long suggests a structural re- adjustment along the Karhova-Tepek6y axis.

(6) Finally, the Varto-~stiikran earthquake seems to have been a short duration sharp shock, probably of very high ground acceleration with a strong vertical com- ponent. The general impression of the writers is that the ground movements were associated with high frequencies.

VARTO USTUKRAN :EARTHQUAKE OF 19 AUGUST 1966 101

ACKNOWLEDGMENTS

During the greater part of the three-week mission the authors were accompanied by Mr. Fahri Ayda~, architect of the Ministry of Reconstruction, Ankara, whose assistance was invaluable. The authors would like to record their indebtedness to the Director of the Reha- bilitation Institute Mr. Fikret Ungan, to the Vali of Erzurum, Mr. All Akarsu and to the chief engineer, Mr. Lfitfi Yfirfir. Many engineers and geologists in Erzurum, Varto Hm~s and Mus gave freely of their time during the busy weeks that followed the earthquake. The authors would also like to thank the staff of the United Nations in Ankara and in particular Mr. E. Ward and Mr. G. Hutton for their generous cooperation. Thanks are expressed to the many Turk engineers and geologists; a mission of this nature under such conditions could not have been carried out without their aid. This paper is published by permission of UNESCO, Paris, and it should be considered as representing the authors' views only and not necessarily those of UNESCO.

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DEPARTMENT OF CIVIL ENGINEERING IMPERIAL COLLEGE OF SCIENCE LONDON, S.W.7.

INSTITUTE OF GEOPHYSICS, CH2 RLES UNIVERSITY, PRAHA 2

Manuscript received February 17, 1967

Technology

Varto Earthquake: 19 August 1966