Earthquakes and natural disasters

Risks of natural hazards caused by natural disaster are closely related to the development process of society. Disasters pose hazard to sustainable development of the country. 75 percent of the world populations live on the territory that suffer from such different disasters such as: earthquakes, floods, hurricane, drought and etc. The effects induced by the natural disasters have caused more than 180 of deaths and 3000 of human losses everyday in the different parts of the world. (EM-DAT, www.em-dat.net).

Upward trend of disaster’s intensity and frequency are observed worldwide (Fig. 1). It is the result of the urbanization and rapid increase of the density of the population, global climate change and economical globalization, environmental deterioration and etc. The natural disasters risk is occurred when the hazardous hydrometeorological, geological and other phenomena interact with physical, social, economical and ecological factors of vulnerable social and environmental infrastructure.

Georgia is prone to the catastrophes . In the last two decades, there have occurred   the following natural disasters: Avalanches in Svaneti and Khevsureti, landslides in a mountainous Achara, floods, hurricane and drought in the West and East Georgia, Racha earthquake of 1991 and Tbilisi Earthquake of 2002. These phenomena are very special both from ecological and from social-economical points of view. By the index of disaster risk obtained by UNDP, Georgia relates to the countries with medium and high level risk. So the natural disasters in Georgia have to be considered as a standing negative factor in the development process of the country. Such approach implies necessity of more active actions by all possible means to reduce the risk of natural disasters at each level and maintain the sustainable economic development of the country.

Recent geodynamics of Georgia and adjacent territories of the Black Sea-Caspian Sea region, as a whole, are determined by the still-converging Eurasian and Africa-Arabian plates. Related tectonic activities caused moderate seismicity in the region. According to geodetic data, the rate of convergence is *20–30 mm/y, of which some 2/3 are likely to be taken up south of the Lesser Caucasian (Sevan-Akera) ophiolitic suture, mainly in south Armenia, Nakhchivan, northwest Iran and Eastern Turkey. The rest of the S/N directed relative plate motion has been accommodated in the South Caucasus chiefly by crustal shortening (DeMets et al. 1990; Jackson and Ambraseys 1997; Allen et al. 2004; Reilinger et al. 2006). Three principal directions of active faults compatible with the dominant near N–S compressional stress produced by northward displacement of the Arabian plate can be distinguished in the region—one longitudinal (WNW–ESE or W–E) and two transversal (NE–SW and NW–SE). The first group of structures having the so-called Caucasian strike is represented by compressional structures: reverse faults thrusts, nappes and strongly related deformed fault-propagation folds. In contrast to these faults, the transversal faults are also mainly compressional structures having somewhat considerable strike-slip components. The tensional nature of sub-meridian faults is evidenced by intensive Neogene–Quaternary volcanism related to these faults in some areas of Southern Georgia (Javakheti Highland) and the Greater Caucasian range. NE–SW left-lateral strike-slip faults are the main seismoactive structures in Northeastern Turkey, the Southern parts of Western Georgia and Armenia. Right-lateral strike-slip faults and fault zones are developed in Southeastern Georgia.

Natural Disasters in Georgia

Current geodynamics and orographic properties of Georgia play an important role for the occurrence of geological (earthquake), geomorphological (landslides, debris flows, snow avalanches), hydrological (flash floods) and meteorological (droughts, hurricanes, lightning, hail, fog, frost, freezing) hazards.

Geological Hazards: Seismicity —over the historical period, the observed seismicity in Georgia is characterized as moderate. All historical and instrumental earthquakes observed (4.5 \ MS \ 7.0) were located along the fault systems of the Greater and Lesser Caucasus

and the intermountain depressions. The maximum magnitude of observed earthquakes is MS = 7.0. The moderate earthquakes reflect the regional tectonics that are largely determined by the position of the Caucasus range between the still-converging Eurasian and Africa-Arabian lithosphere plates. By this classification, the southern slopes of Greater Caucasus are characterized by thrust and thrust strike slips, while the Javakheti upland is mostly characterized by strike-slip faults. The Kura depression is characterized by thrust and trust-right-lateral strike slips. Earthquakes in Georgia are associated with secondary events such as landslides, debris flows and rock falls, as such, to provide an example, Racha earthquake in 1991 caused about 20,000 landslides (Tatashidze et al. 2000).

Geomorphological hazards: landslide, debris flow, snow avalanche —Georgia belongs to one of the most complex hazardous mountain regions in terms of heterogeneity of formation of landslides, debris flows and snow avalanches, and damage resulting from these geomorphological hazards to territories is considerably high due to the frequency of

occurrence (Gobechia et al. 2009). Hence, the risk to the population and to economic and engineering facilities is remarkable.

Hydrological hazards: Flash floods and flooding  cause increased water levels in the rivers of Georgia. Flooding is often characterized by a river water regime phase influenced by melting of snow accumulated in rivers during cold seasons, as well as melting of glaciers in high Caucasus mountains. The increase in river water levels caused by melting of snow only has a short duration but the disposition lasts for about 3 months. In some river basins (such as Kodori, Enguri, Rioni and Tergi), which are additionally fed from glaciers, the spring flooding lasts for up to 6 months. Usually, the flooding is not associated with a disastrous increase in water level and flow velocity is very slow. In contrast, flash floods result in an irregular transitory increase of water levels in rivers. Flash floods are caused by intensive precipitation in the watersheds, and flow velocities are comparatively high (Dolidze et al. 2009).

Western Georgia is characterized by high atmospheric precipitation during almost the entire year. However, less rainy periods are observed in spring time (Elizbarashvili 2007). During this period, the soil and air are relatively warm, but the sea surface and the air temperature around are still low. This leads to the formation of a stable vertical stratification in the lower atmosphere layers that prevents the upward flow of humid air into the higher atmosphere and hence the formation of rain. Therefore, extensive flooding and disastrous flash floods caused by heavy rain are relatively uncommon in Western Georgian river watersheds during April and May. As a matter of fact, in the section near Chaladidi village (near the Black Sea), the Rioni river—the most water-abounding river of Georgia—has reached its maximum rate of discharge not during a warm season but on 01 February1987 when the discharge rate was 4,850 m3/s. In the Eastern part of the country, rains are most intensive during May and June. However, other summer months and rarely Sep-tember are also characterized by very heavy local precipitation intensities. Mtkvari (Kura) river and most of its feeders are characterized by dangerous flash floods during April and May. However, sometimes some feeders of the Mtkvari River experience dangerous flash floods in summer, as well as rarely in September.

Meteorological hazards:

Drought – Drought is a frequent phenomenon in Eastern Georgia. The drought frequency exceeded 40 % in the 1980s in some areas by certain early estimates. As a result of frequent droughts accompanying the global warming in past decades, a transformation of many types of natural landscapes has been observed. The desertification probability of steppes and semidesert landscapes in Eastern Georgia has reached 25–30 % by the end of the twentieth century. According to official figures, an area of approximately 200,000 ha is strongly affected (Elizbarashvili and Elizbarashvili 2012). Property damage caused by drought is significantly high (Elizbarashvili et al. 2009). On the territory of Georgia, the following six main types of atmospheric processes determine weather conditions: Siberian anticyclone, Mediterranean cyclone, Azores anticyclone, polar basin anticyclone, wave disturbance in the south and local anticyclone. Repeatability of each type of processes varies depending on the season. Drought in Georgia occurs in polar, the Azores and mixed types of synoptic processes, frequency of which increases in the warm season. Long dry periods are formed in 70 % polar, 15 and 30 % of Azorean mixed types of synoptic processes (Elizbarashvili 2007). The main meteorological factors for drought formation are dry weather, high temperature and a lack of soil moisture. While the average time of periods with precipitation <5 mm is not more than

10–15 days per year, the mean rainfall does not exceed 200–300 mm during the vegetation period in the lowlands, which repeatedly causes severe threats to the agriculture. At the same time, air temperatures sums C10 C during the vegetation period exceed 4,000 C, and the mean duration of continuous high temperatures C30 C is exceeding 4 h per day.

Hurricanes—a wind storm is considered as hurricane if the velocity is exceeding 30 m/s. These winds cause considerable damage to the economy and population: they damage buildings, communication and power lines, cause traffic delay, roughness in the sea and reservoirs, dust storms, displacement of snow, soil erosion and other adverse effects. On the territory of Georgia, hurricanes have mostly westerly or easterly direction. The former occurs during cyclone passages of Mediterranean origin or if a low pressure associated with Atlantic cyclones over the South Caucasus occurs. In this case, the pressure gradient is directed from west to east, which leads to a strengthening of the western and north-western winds. Eastern winds occur when over the central and Eastern regions of the Caucasus, an area of high pressure has been formed, and from the west, a cyclone extends over the Black Sea. In this case, which is mostly observed in Western Georgia, the pressure gradient is directed from east to west and easterly winds grow stronger.

Hail is a frequent phenomenon especially in Eastern Georgia. An economic loss from the hail is very significant every year (Amiranashvili et al. 2002, 2008).

Frost is understood as lowering the minimum air or soil surface temperature below 0 C on the background of positive daily mean temperatures. Frost starts earlier in the ground than in the air, even if air temperatures are around 1 C. Therefore, atmospheric frost always includes the freezing of soil. Frost is a dangerous phenomenon for agriculture, and crop damage is observable after plants have been grown accompanied by a rapid decline in their frost resistance. Therefore, frost is particularly dangerous during frost-free periods, that is, during the period between the mean dates of the onset of the last spring frosts and the first autumn frost. This kind of period is mainly characterized by advective–radiative frosts, which are formed as a result of the invasion of cold air and the subsequent cooling by nocturnal radiation. Such frosts occur frequently in late spring and early autumn, and in the mountains—even in summer— although they are rare compared to frost during the entire vegetative season, which have been properly studied both for Georgia and the Caucasus in general (Elizbarashvili et al. 2011). In significant parts of Colchis Lowland,Shida Kartli and the central part of the Great Caucasus frosts of moderate intensity are dominant when the minimum temperature during frosts decreases to -4 C. In such situation, plants with mean frost resistance will be damaged. On large territories of Eastern Georgia, especially in the region of Shida Kartli and in the inner zones of the Colchis lowlands, frost with strong intensity (minimum temperatures between -4 and -8 C) is common and severe damages to a significant portion of the cultivated plants are observed. In some mountainous zones of Guria, Adjara and Eastern Georgia, air temperature falls to -8C and below. This is a very strong frost intensity at which even frost super-resistant plants and grains, early dandelion, barley and other crops are damaged.

Fog is a frequent phenomenon on the territory of Georgia. Fog days exceed a sum of 150 day per year in some regions, and on the glacis of the Surami ridge at 1,243 m a.s.l. foggy weather conditions last approximately 260 days (Elizbarashvili 2007). Impairing visibility, fog firstly delays any traffic movement. The most dangerous phenomena are caused by fogs when the visibility is less than 50 m. In this case, a collapse of any kind of transport is possible. Especially in mountainous areas, this results in emergency situations and an increasing number of accidents leading to fatalities. Depending on the basic

physical processes of formation, on the territory of Georgia, the following kinds of fogs are observed: radiative, advective (including evaporative fogs), advective–radiative, frontal and orographic. Their distribution over the area is complex, due to a variety of physical and geographical conditions and peculiarities of atmospheric circulation. Nowadays, the geographical allocations of the number of days and the total duration of fog on the territory of Georgia have been studied in detail (Elizbarashvili et al. 2012). The probability of fog formation in a particular location and area, the empirical function of allocation of foggy days and the main areas of their distribution on the territory of Eastern Georgia have been subject to extensive research (Elizbarashvili 2007; Elizbarashvili ESh and Zubitashvili 2007). The share of dangerous mists in the total number of foggy days is more than 70 %. On a significant part of the territory, fogs of long duration exceeding 10 h are common. In addition, there are isolated centres, in particular along the Black Sea coast, in the Kvemo Kartli region and in Southern Georgia, where fogs with moderate (7–9 h) and mean duration (4–6 h) are dominant.

Freezing of wires has a negative effect on the production processes of many industries. Freezing disturbs the normal operation of communication air lines and power lines, causing damage to the transport sector, to agriculture and forestry. Freezing of wires is not uncommon in the mountainous regions of Georgia. Therefore, the study of this phenomenon has a long history (Elizbarashvili and Elizbarashvili 2012). However, the reliability of the previous studies is doubtful, and the resulting maps are considered to be rather sche-matic than analytic. Therefore, these earlier works on freezing requires editing and revising. Wire freezing takes place in some individual local areas of the country, as well as over larger regions. The most typical aspect for the formation of glare freezing in the whole Southern Caucasus is a cold front influencing the region mainly from the west, in particular, the Black Sea, and more rarely from the east, the Caspian Sea. This cold front breaks into a territory occupied before by warmer and more humid air masses. As a result, warm air masses rise along the inclined surface of the cold front, and consequently, nimbostratus clouds and precipitation necessary for icing are formed behind the front.

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