Natural emergency situations

Here the characteristic for some natural catastrophes is given.

The earthquake is the force shacking of the earth's crust induced by tectonic or volcanic cause that results in ruin of structures, fires and people victims.

Main earthquake characteristics are size of hit site, magnitude, intensity of energy on the earth surface. Earthquake’s size of hit site can be of 10..30 km, sometimes it is much more.

Magnitude characterizes general energy of earthquake and represents a common logarithm of ratio of maximum ground oscillation amplitude measured in the investigated place by seismograph in microns to maximum amplitude of ground oscillation defined on the distance of 100 km from the epicenter.

Magnitude (M) by Richter scale is measured from 0 up to 9 (last number corresponds to the most powerful earthquake).

The intensity of energy on the surface of the ground is measured in numbers. It depends on hit site size, magnitude, distance from epicenter, geological structure of the ground. For earthquake energy intensity measurement in our country 12-numbers Richter scale is accepted.

Table 5

Earthquake characteristic

Magnitude by Richter scale	World annual average rate of earthquakes	Earthquake duration, sec	Radius of hit site, km
8,0..8,9		30..90	80..160
7,0..7,9		20..50	50..120
6,0..6,9		10..30	20..80
5,0..5,9		2..15	5..30
4,0..4,9		0..5	0..15

The earthquakes bring large material losses and kill thousands people. For example, on June 21,1990 during earthquake having intensity of 8 numbers by the Richter scale at northern Ural in the province of Shlyan more than 50,000 people perished and about 1,000,000 people were injured and left out of living places.

Table 6

The largest earthquakes of XX century

Year	Place	Victims (thousands)
	Ganyasu (China)
	Fokto (Japan)	over 100
	Agadir (Morocco)
	Chimbote (Peru)
	Tanshan (China)
	Iran
	Armenia

Protection from earthquakes implies beforehand detecting of seismic dangerous zones in various regions of country, that is seismic zoning. On maps of seismic zones where earthquakes of intensity above 7..8 numbers by Richter scale are possible are marked. In such regions they carry out various protective measures, chemical factories and nuclear power stations are not admitted to build in.

Flood is a significant water filling of district after increasing of water level in river, lake caused by various reasons (rain, ice jam on the rivers, dam destruction and other). Floods result in material losses and human victims.

At the beginning of July, 1990 heavy showers in Zabaykallia caused the flood which destroyed 400 bridges and brought the losses of 400,000,000 in national currency. Thousands people remained without living place or perished.

Floods can cause fires as the result of short-circuit of power cable, and also destruction of pipes, electrical, television and telegraphic networks.

The main direction in flood struggle is decreasing of maximum water gain in a river by the redistribution of the flow in time (preservation of plants near water, planting of forest shelter belts etc). For the protection from flood the system of dams is used.

Land-slide is shifting of mountain masses down the slope, that appears because of equilibrium breaking caused by many reasons (ground undermining, unreasonable economic activity etc).

Land-slides can take place in all hills with slope 200 and more in any season. They differ both in speed of mass moving (slow, middle and fast), and in scale. The slow slides speed makes tens centimeters per one year, middle - some meters per hour or 24 hours, fast - tens kilometers per hour and even more. Only fast slides can get the cause of catastrophes with people victims. For example, in 1911 in the Pamirs the powerful earthquake induced large land-slide. Near 2,500,000,000 m³ of loose masses moved down. Village Usoi with 54 residents was dumped. The land-slide has parted off the valley of the river Murgay and created the dump lake which has flooded the village of Saraz. The height of that natural dam reached 300 m, depth of the lake - 284 m and length - 53 km.

Precaution measures are transformation of ground relief, fixing of a slope by piles, construction of supports.

Snow avalanches are also referred to land-slides and appear as sliding displacements. Gravity makes displacement of snow masses down the slope. Snow avalanche is a compound of snow crystals and air. Large avalanches arise on 25..600 slopes. For example, on July 13, 1990 in the Pamirs the earthquake and snow avalanche demolished camp of the climbers, which was located on the height of 5300 m, 40 men perished.

The protection from avalanches can be passive and active. In passive protection protecting shields are applied. In active protection avalanche-dangerous slopes shooting is carried out.

Mudflow is a flood with a very large concentration of mineral particles, stones, fragments of mountain rock (what makes from 10..15 up to 75 % of total flow volume), which occurs in pools of small mountain rivers and is caused by rain, sometimes by intensive snow thawing. Danger of mudflow consists not only in its destroying force, but also in suddenness of its origin. Mudflow can be of mud structure (mixture of water and melkozem), mud-stone structure (mixture of water, rubble, gravel, small stone), water-stone structure (mixture of water and large stone). The mudflow speed reaches 2,5.. 4,0 mps, and sometimes up to 8..10 mps. Mudflow consequences are sometimes disastrous. On July 8, 1921 Alma-Ata was hit by the mass of the ground, stone, snow, sand accelerated by the water flow. That flow demolished structures, people, animals. The buildings were taken off the foundation and together with people taken by a rough flow.

One mudflow was caused by the showers in the pool of the river Mala Almaatinka. The total volume of mud-stone masses made near 2,000,000 m³. The flow intersected city by 200-meter band.

Methods for mudflow struggling are various. These are structure of various dams, cascade of jams, supports, ditch etc.

Hurricane is a wind having force of 12 numbers by the Bofft scale, that is the wind blowing over 32,6 mps (117,3 kmph). Hurricanes are also tropical cyclones which arise in the Pacific ocean near Central America; on the Far East and the Indian ocean hurricanes are named as typhoons. In hurricanes the velocity of the air reaches more than 50 mps. They are followed by heavy showers.

In December, 1944 near the Philippines the ships of the 3rd USA Navy turned out to be near the center of the typhoon. Three destroyers drowned, other 28 ships received damages, 146 planes and 19 hydroplanes were broken and got out of the board, more than 800 people perished.

Hurricanes and storm wind (20,8 up to 32,6 mps by the Bofft scale) in winter can rise plenty of snow in the air making a snowstorm. From hurricane wind and large waves in East Pakistan about 10,000,000 people suffered and approximately 500,000 perished on November 13, 1970.

Modern methods of the weather forecast allow a couple of hours or even a day before to warn people about hurricane coming up. The most reliable protection from hurricanes is using of protective structures (subway, cellars of houses, underground transitions etc can be applied as).