Perhaps there is no place on earth where people do not face the threat of this or that natural disaster. Every year hurricanes, whirlwinds, avalanches, landslides and creeps mow off tens and hundreds of thousands of lives. However, mankind has learnt how to stand up to these calamities in the aquatic or air environment or quickly respond to them; expert forecasts allow to minimize the aftermath. However, there are many disasters which we are unable to forecast, even though their consequences are really frightening. Like those of earthquakes and tsunamis.

Catastrophes occurring due to tectonic movements of the earth crust are discussed by Yuri Golubchikov in an article published in the Energiya (Energy) journal. The author points out that magnitude of an earthquake and its destructive force are two different things. The most violent earthquakes (up to 11 points on the seismic scale) on the territory of our country took place in sparsely populated regions of the Baikal Rift Zone, and no one remembers them. But the earthquake that hit Ashkhabad in 1948 (8 - 9 points, the most violent earthquake on the USSR territory in the number of victims - 110 thous. people), and one in Tashkent (1966, 8 points) will be remembered forever, through the authorities tried to hush up or understate the toll in dead and destructions - even natural disasters were supposed to spare the country of victorious socialism... Everyone remembers the Spitak earthquake of 1988 in Armenia (25 thous. people killed*) - that time on the wave of "the policy of openness" Soviet citizens came to understand: apart from the verbal husks about working-class solidarity, there were also a compassion, grief and charity.

The author speaks not only about the social aftereffects of tectonic catastrophes, but also about economic losses-actual and potential. In particular, he tells about the project of laying a Taishet-Vladivostok oil pipeline through the northernmost part of the Baikal Rift, i.e. in the most seismically dangerous region of Russia. Although the designers realized the danger, their technical precautions were not adequate to the threat of an ecological catastrophe, inevitable in case of a strong earthquake, the author says. According to the project the pipeline was to be laid in 80 - 90 km from Lake Baikal, the deepest in the world, in its catch basin. Mountain relief of the region is another danger: the pipeline can be destroyed by a large seismic landslide or creep which can be touched off even by a moderate earthquake. In this case oil will leak out to Baikal in less than two days which, by the way, contains more than 99 percent of this country's fresh water.

No matter now dangerous the inland earthquakes may be, they are local in scope, and even the most violent and destructive ones affect an area of tens of square kilometers, which facilitates rescue operations and rehabilitation. In this respect tsunamis pose more danger: they occur due to seabed subsidence in the process of seaquakes.

* See: "Disaster in Armenia: Forecasts and Reality", Science in the USSR, No. 4, 1989. - Ed.

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The tsunami problem moved to the fore after a disaster in Southeast Asia at the end of December 2004*. However, coastal regions located in the area of high seismic activity had often suffered from this calamity before, too.

The most terrible thing about tsunami is this: a giant tidal wave breaks all of a sudden upon vast coastal areas. Approaching dry land, it slows down fast, grows in height, and hits the shore. Although usually the height of waves in plainlands does not exceed 5 - 6 m, in narrow bays and gulfs it can be more than 20 m high. The most destructive tsunami on the USSR territory occurred on

* See: "Technology of Prevention of Seismic Strikes", Science in Russia, No. 4, 2005. - Ed.

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November 4, 1952, when it hit the town of Severo-Kurilsk located on the Paramushir island. The first wave was 19 m high, the others were a bit lower. The part of the town which was located 50 m above the sea level was wiped out.

Another danger of tsunami is that a strong earthquake sends a wave that can reach regions of low seismic activity where the population does not know how to meet such disasters. It is clear that such catastrophes happen very rarely but they cause huge destruction.

The earthquake that occurred on December 26, 2004, under the seabed of the Indian Ocean near Sumatra triggered such kind of disaster. A series of 47 shocks (the strongest-8.9 points) sent giant tidal waves of about 20 m high which devastated coastal areas of eight countries-Indonesia, Thailand, Malaysia, Sri Lanka, India, the Maldives, Bangladesh, and Myanma. After the first shocks came weaker ones ("aftershocks"). The people who survived after the tragedy of December 26, 2004 panicked and thus aggravated chaos in the disaster zones.

In-water measurements carried out soon after the earthquake showed that in the hypocenter the sea-floor relief changed beyond recognition-blocks of earth material of more than 1.5 km long moved on as far as 11 km, and the total mass of displaced material is estimated at billions of tons.

As mentioned above, seismic forecasts are still unreliable. However, even in antiquity people noted that before earthquakes old water sources disappeared and new ones came up; domestic and wild animals behaved in a strange way, too. But this is not observed everywhere and besides, these observations do not apply in conurbations where one can hardly find water springs or wild animals.

Retrospective analysis is not reliable for forecasting either. Of course, ancient records and chronicles are full of materials about earthquakes and tsunamis of the past. But chroniclers who lived in seismically stable regions, for example, the Russian Plain, accurately recorded any acts of God, including minor seismic tremors. But only large-scale phenomena, i.e. something extraordinary, were recorded in the seismically active countries.

In the situation when earthquake forecasting and prevention is still impossible, people have to screw up their courage and patience to learn to live in seismically dangerous regions. Besides, the number of victims and volume of wreckage increase as mankind keeps destroying natural safeguards, weak as they are. Thus, Yuri Golubchikov believes that the tsunami of December 26, 2004, would not have claimed so many victims, had man spared mangrove thickets and coral reefs-they would have cushioned the tidal wave impact. The conclusion is obvious.

Yuri Golubchikov, "Tectonic Catastrophes of Yesterday and Today", Energiya, No. 8, 2005

Prepared by Andrey BIRYUKOV

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