The 2002 Tbilisi earthquake occurred on April 25 in the

Caucasus The Caucasus () or Caucasia (), is a region between the Black Sea and the Caspian Sea, mainly comprising Armenia, Azerbaijan, Georgia, and parts of Southern Russia. The Caucasus Mountains, including the Greater Caucasus range, have historically ...

country of Georgia. The United States' National Earthquake Information Center (NEIC) placed the magnitude at 4.3 and 4.8 . This moderate magnitude event resulted in a maximum MSK intensity of VII (''Very strong'') to VIII (''Damaging''). An independent investigation estimated the total losses at $160 million (US) while the

Centre for Research on the Epidemiology of Disasters The Centre for Research on the Epidemiology of Disasters (CRED) is a research unit of the University of Louvain (UCLouvain). It is part of the School of Public Health located on the UCLouvain Brussels Woluwe campus, in Brussels, Belgium. CRED has ...

estimated the total losses at 350 million. Between five and seven were killed, 52–70 were injured, and more than 1,000 were left homeless.

Tectonic setting

Tbilisi lies near the northern boundary of the complex zone of deformation associated with the continuing collision between the Arabian Plate and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

. To the north, the mountains of the Greater Caucasus are a result of active

thrust tectonics Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, ...

, linking eastwards to the

Apsheron sill The Apsheron Sill, Absheron Sill, Apsheron Ridge or Apsheron Threshold is a major northwest–southeast trending bathymetric high that runs for about 250 km across the whole of the Caspian Sea from Baku in Azerbaijan to the Cheleken Peninsula in Tu ...

. To the south, the Lesser Caucasus mountains are also a result of active thrust tectonics. The whole Caucasus region is affected by earthquakes, with the largest known being associated with the active front of the Greater Caucasus thrust belt, such as the

1991 Racha earthquake The 1991 Racha earthquake occurred in the province of Racha, Georgia, at 9:12 UTC on 29 April. Centered on the districts of Oni and Ambrolauri on the southern foothills of the Greater Caucasus mountains, it killed 270, left approximately 100, ...

. Tbilisi itself has relatively low seismicity, although there are historical records of damaging earthquakes, such as the event in 1896, which had an estimated intensity of VII ( MSK), the strongest known earthquake to have affected Tbilisi during historical times.

Earthquake

The earthquake was preceded by a series of

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

s, of which the largest was M 3.5 on April 11. The mainshock had an estimated magnitude of 4.7 (ISC), 4.8 (ANSS), 4.5 , with an estimate hypocentral depth of 13.6 km (ISC), 10.0 km (ANSS), 5.0 km and 3.0 km. The mainshock produced higher intensity shaking than would normally be expected for an earthquake of that magnitude. The frequency was also unusually high (maximum 5 Hz) and the duration was short. The epicenter was located centrally within the city of Tbilisi, something that had not been considered in earlier studies of potential seismic source zones.

Damage

The unusually high frequency of the shaking, combined with the short duration, meant that there was little damage to larger buildings or those built using

reinforced concrete Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...

. The most affected buildings were, in contrast, low-rise brick or stone built, which were concentrated in the older part of the city. Buildings affected during the mainshock were further damaged by some of the aftershocks. A total of 18,000 households were badly affected, leaving 69,000 people homeless. There was also significant damage to some schools and hospitals. Between five and seven people died as a result of the earthquake and a further 52–70 were injured.

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