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Macroseismic analysis of epicentral zone of  Dec, 14  2000 earthquake in Georgia  

V.Zaalishvili, A.Odisharia, I.Timchenko, M.Otinashvili, S.Gogmachadze, Z.Zaalishvili   

On Dec, 14 2000 an earthquake occurred in Georgia with a magnitude М=3.5-3.6. The epicenter location was 12 km to the South from Tbilisi; coordinates: j=41.62⁰, l=44.70⁰. The depth of the event was 10 km. The instrumental epicenter was calculated in the Department of Regional Seismology of Institute of Geophysics of Georgian Academy of sciences according the data, recorded in seismic stations. Unfortunately, for some reasons (rather low level of seismic effect, financial difficulties of the state scientific institutes etc.) macroseismic investigations of the consequences of this earthquake were not carried out immediately after the earthquake. At the same time this information has scientific and practical importance. For, as a rule, an instrumental epicenter, often does not coincide with the seismic effect. Besides, each earthquake should be estimated by its manifestation etc. And at last, the detail examination of consequences of even weak earthquake gives the new data of engineering-seismological conditions, allows to adjust zones of active faults etc.

In this connection, during fulfillment of the present project a special expedition of the Institute of Structural Mechanics and Earthquake Engineering of Georgian Academy of sciences has been organized and consisting of V.Zaalishvili (Head of Department of Engineering Seismology); A.Odisharia (Head of  Sector of Seismic Microzonation  of  Department of Engineering Seismology); S.Gogmachadze (Head of  Sector of Engineering-Geological Investigations of Department of Engineering Seismology);  I.Timchenko (Senior scientific researcher of Laboratory of Earthquake Resistant Structures); M.Otinashvili (Scientific researcher of Department of Engineering Seismology); I.Javrishvili  (post-graduate student of the Department of Engineering Seismology); Z.Zaalishvili (post-graduate student of the Institute of Economics of Georgian Academy of sciences). This structure of expedition (geophysicists, geologists, structural engineer, mathematics, economist) supposed the complex examination of the earthquake consequences. Before the expedition the macroseismic examination of territory of. Tbilisi was carried out. In addition to engineering examination of the territory, the method of questionnaire zonation was used. Such questionnaire zonation allowed to take into account sensations of the population for an estimation of the earthquake intensity in conditions of rather weak effect. The main results are presented below.

Brief information about the territory.

Relief and soils. Mountains occupy almost 70 % of the territory; broad river valleys and mountain plateaus occupy the remaining territory. The absolute altitudes change from 300 m up to 2203 m (Trialeti mountain ridge). The left bank of the Kura river represents a series of  mountain ridges, separated by rivers, plains, and vast hollows. Prevailing absolute altitudes 600-1200 m (maximum 1733 m).

The mountain ridges have width of 100-300 m, with spherical top; steep slope  is 15-35⁰ (up to 45⁰). The river and stream valleys are of trapezoidal and canyon form, prevailing steep slope is 30-60⁰ (breakaways have the depth of 3-8 m).

Mountain ridges on the right bank of the Kura river have prevailing absolute altitudes of 800-2000 m. Ridges are of 50-500 m in width (sometimes 30 m), steep slope  is of 10-45⁰ (up to 55⁰).  River valleys have canyon form, with a depth of 40-100 m. Steep slope is up to 60⁰. There are (here and there) rocky breaks and cornices with altitude of 4-20 m.

 The mountain plateaus are situated at the altitudes of 1200-1750 m. The surface of a plateau predominantly is flat or slightly corrugated; relative altitudes are up to 100 m.

The river valleys  have slopes with  height  up to 60 m,  steepness is 20-60⁰, breaks 5-20 m. Their overcoming is possible only on existing paths. Large plains and  river valleys have absolute altitudes of 300-650 m.

 Relative altitudes are of 5-25 m (up to 40 m). A surface is flat, terraced (altitude of terraces is from 3 up to 200 m), split by the rivers, ravines, gorges and girders and irrigation ditches.  Soils crushed-stone-loamy, clayey and loamy. The level of groundwater table is from 0 up to 80 m.

Hydrography. The Kura river flows in broad valley (width 1 - 3 km, maximum – 7.5 km) with well developed flood-plain (width of 0.2- 3 km). Width of the river is 20-160 m, depth of 0.3- 3.0 m (maximum 8 m), prevailing flow rate is of 0.8-2.5 m/s. A bottom is sandy-pebble, less often stony. River-bed is sinuous. The banks have altitude of 1-4 m and (in few places up to 20 m). Lakes Kumisi and Lisi have a depth of 1-5 m. A bottom is flat, banks are slimy in some places. Water is fresh (in Kumisi is bitter-salted).

Geographic map of the Tbilisi  region is shown in Fig. 1. Epicentral zone of the earthquake is shown in Fig. 2.

 

Fig. 1. Geographic map of the Tbilisi  region

Fig. 2. Epicentral zone of the earthquake

  

Village Kvemo Teleti (Fig. 3). In a village there is a small manifestation of the earthquake in buildings (damage grade - 1).

Buildings are new constructed, in general 2-storey, erected of brick or small-sized blocks. Roofs are of tin-plate. There is a small amount of old buildings of brick masonry. The village is on clayey soils. A ground-water level is of 8-13 m. At the earthquake the vertical shock was felt. The inhabitant of village B.Kitiashvili has notified that before the earthquake the animals were frightened. The ware rung, the chandeliers oscillated. The population were frightened .

 

Fig. 3. Kvemo Teleti. General view.

Fig. 4. Kvemo Teleti. View from the Shavnabad monastery.

 

Monastery Shavnabad (Fig. 5).  Actual appearance has  from a beginning of the 19th century. It was erected without antiseismic measures of a good quality brick masonry. Has not symmetrical shape in plan. Is situated on the top of a mountain. The inhabitants of a monastery – monks, have told, that felt vertical shock at a prayer. There was a roar before the earthquake. One brick has failed from the top of the masonry bell tower. There were no other visible damages. 

 

Fig. 5. The Shavnabad monastery.

   

Fig. 6. The Shavnabad monastery. General view from the main road.

 

Village Tsalaskuri. Manifestation of the earthquake is the same like in Kvemo Teleti. Foundation soils are of diluvium.

Village Kumisi (700 houses). Before the earthquake the noise was felt. At the earthquake the chandeliers oscillated, the structures scratched. The ware rung (but did not fail). The frightened people ran outdoors and stayed in the street some time. Some buildings of brick masonry without ASD (vulnerability type A) received damages of 3-4 grade. The masonry on clay mortar is widespread in the village. In  Fig. 7 the house of Vano Mdivnishvili is shown. In addition to failed masonry it received cracks in walls and in wall intersections in corners; crack width is up to 2 cm.  Most of buildings suffer damages of  grade 1.

 

  Fig. 7. Kumisi village. Failed stone  masonry.

 

The house of Otari Mazmishvili  (Fig. 9) of brick masonry on weak mortar, without ASD, was built on a slope of 15⁰; suffered damages of grade 3. The aged construction, situated nearby, of stone masonry with very poor quality was damaged before the earthquake (Fig. 10).

   

Fig. 8. Kumisi village. Cracks in wall corner – the same building.

 

  Fig. 9. Kumisi village. Inclined crack in the wall partition.

Fig.10. Kumisi village. Crack in the wall partition, increased after the earthquake. Effect of the landslide.

   

A new-constructed two-story building (Fig.11, 12) of brick and stone masonry  without  antiseismic belts received a vertical crack of width up to 1 cm.  

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Fig. 11.  Kumisi village. Crack in the wall partition, increased after the earthquake, failed bricks.  

 

 Fig. 12. Kumisi village. Vertical crack in the wall.

 

Fig. 13. Typical relief.

  Village Vashlovani. Is situated on a mountain slope. Three times in XVII century were completely destroyed by plundering raids of leki people. There is a high fortress-tower at present as a church. The level of underground water is approximately of 6 m. The inhabitant of village M.Menteshashvili has notified, that they have felt a strong  vertical shock and before -  a noise, bay of dogs and roar of cattle;  panic of the population. The population ran outside in the street.

The house of Murad Menteshashvili was built in 1965; constructed of brick and stone masonry without ASD.  The door and window lintels were damaged (Fig. 14 ). In a back wall the bricks were dropped out from window lintels as well (Fig. 15).  A vertical crack was appeared between external and middle internal wall with the width of 1 cm (below) and 5 cm (above) because of a poor brick bond (Fig. 16).  The brick chimney was not damaged. In many buildings there are damages of 1-2 degree.

 

  Fig.14. Vashlovani village. Stone-brick building without ASD.

Fig. 15  The same building. Damage of  window and door lintels.

 

Fig. 16. The same building. Damage of the wall intersection.  

Village Ertsisi. The village Ertsisi borders with Vashlovani. The population felt vertical impact. The same manifestation of the earthquake, as in Vashlovani. The wall of a cow-house has fallen.

Village Borbalo  (approximately 120 houses), founded in XVII century. 36 houses are closed because of absence of their hosts. All buildings are without antiseismic measures. Typical damages - cracks in stone masonry. Some cracks appeared at the Spitak (1988) earthquake in Armenia, like in the house of Karlo Iremashvili, built in 1975. At the earthquake in December the cracks enlarged, the cracks in the ceiling contour appeared. The cracks between wall and attached RC balcony slab with a stairs appeared. The building has  damage grade 2.

Village Goubani (200 houses). Buildings, situated on a hill, received more severe damages. Most of buildings have damage of 1-2 grade, some buildings have damage of grade 3. All buildings are without antiseismic measures. Foundation soils -  clay up to 4-5 m, then layers of argillites, no underground water. In the bottom  part of the village the shock was vertical, the duration of the earthquake was shorter then at the Spitak earthquake. The inhabitants heard a noise before the earthquake. The population ran in the street. The inhabitant of the village L.Giorgashvili told, that at the earthquake the horizontal oscillations dominated. The vertical cracks in intersection of walls, in the opening corners appeared. The inhabitants heard a noise before the earthquake.

Other inhabitant of village O.Sultanishvili notified, that there was a panic, ware and glasses failed.

 

  Fig 17. Goubani village. Damage of the wall.

 

  Fig. 18. Goubani village. Damage of the silicate brick wall.

   

Fig .19. Goubani village. Vertical failure in the brick wall with low ASD level.  

Some buildings have received damage of grade 4. The 2-story biulding of Nodari Sulhkanishvili was built without antiseismic measures. Newer addition on a concrete foundation borders to the house. The back wall failed (Fig. 20). Mortar is of very poor quality. The wooden beams of a roof slab pushed a wall out of its plane. Bonding of masonry in intersection of walls was missing. A front part of building with wooden gallery and brick masonry is without damage (Fig. 21).

 

Fig. 20.  Goubani village.

   

Fig. 21  Goubani village. Front view of the same building.

 

In adjacent buildings the horizontal contour cracks appeared in the ceiling and in a top level of window openings, width 2-4 mm. According to suggestions of the inhabitants, the fail of ware from a case took place. Cracks in the corners of openings and in window-sill masonry correspond to grade 2-3 (Fig. 22).

 

Fig. 22. Failures in the wall. Goubani village.

In Fig.   23. The house of Suliko Matarashvili, is shown. The fence was deformed before the earthquake.

 

Fig 23. Goubani village.  Damage grade 4. Fence deformation.

 

Village Djordjiashvili is situated on the terrace of a hill. The inhabitant of village Valiko Okuashvili notified, that the population felt a strong roar (similar to explosion), the ware rattled. The people frightened, ran outdoors. The oscillations of a soil were horizontal.

Some buildings of class A received degree of damage 4. In Fig. 24-27 the house of V.Okuashvili is shown. The wall failed, it was damaged before the earthquake.  In the photo of the back site the cracks have width up to 5 cm (Fig. 27).

   

Fig. 24. Djоrdjiashvili  village. Damage grade 4.

 

Fig. 25. Djоrdjiashvili  village. Damage grade 4.

 

Fig. 26. Djоrdjiashvili  village. Damage grade 4.

 

 Fig. 27. Djordjiashvili village. The same building. Vertical crack in the wall.

 

Fig. 28. Djordjiashvili village. Damage of the wall without ASD.

At the boundary of the village the phenomenon of landslide (Fig. 29) was observed.

Fig.29. Phenomenon of  landslide at the boundary of v. Djordjiashvili.

 

Fig. 30.  Djordjiashvili village. Building without ASD. Damage grade 4.

Village Asureti is situated on the opposite terrace of a hill - on the another bank of a gorge (Fig. 31). The village is large. The inhabitants felt a small, then large shock, then continuous horizontal oscillations. There was no roar. Many buildings have damage of  grade 1.  

Fig. 31. Influence of relief on intensity of the earthquake

  Village Enageti is mostly situated in a hollow of a foothills. Inhabitant of the village L.Mestvarishvili notified, that the earthquake was not felt by him. The most part of inhabitants felt horizontal oscillations and a roar.

Village Mukhati is situated in a valley. Few buildings received damages of grade 1.

Village Tabakhmela. Inhabitants of the village felt horizontal oscillations, heard racking of ware. In few houses the damage grade is 1. In few houses fall of small pieces of plaster, hair-line cracks appeared. Existing cracks increased.

Village Shindisi is situated below Tabakhmela. Inhabitants felt vertical shock. In few houses damage of  grade 1.

Village Tskhneti. Few buildings have grade of damage 1. Inhabitants felt vertical shock.

Villages Kodjori, Kiketi  Inhabitants felt vertical shock. Few buildings have of damage grade 1.

 

Tbilisi city (12 km from the epicentre). The earthquake was felt as a vertical shock and subsequent gentle horizontal shocks. Many inhabitants felt a fright. Few buildings have received damages. Examples of damaged buildings are shown in Fig. 32-37. All these buildings are without ASD. .

 

Fig. 32. 5, Lermontov str. Cracks in the building increased, the fence was damaged before the EQ.

Fig. 33. 8, Michael Zichi str. Collapsed building.

 

Fig. 34. Child, saved at the EQ by her mother before the collapse of building.

Fig. 35. Increased cracks in the adjacent building. M.Zichi str.

 

Fig. 36. Increased damages in the brick building. Chaikovski str.

 

Fig. 37. 10, Peritsvalebis str. Vertical cracks in the brick wall appeared.

The record of the earthquake was made in seismic station of geophysical observatory of the Institute of Geophysics of Georgian Academy of sciences, situated in Saburtalo district, Tbillisi. Foundation soil is sandstone. The record was kindly presented to us for processing by our colleagu es from the Institute of Geophysics. The record and its Fourier spectrum are shown in Fig. 38, 39.

  Fig. 38. Record of the Dec, 14, 2000 earthquake

 

Fig. 39. Fourier spectrum of the record of the Dec, 14, 2000 earthquake

 

The map of isoseisms of the Earthquake is shown in Fig. 40. Macroseismic intensity of the epicentral region is given in Tab. 1.

   

Fig. 40. Map of isoseisms.

1

Macroseismic intensity of the epicentral region

 

Photos: Igor Timchenko

GIS: Maya Otinashvili

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