Файл: Диссертация тема работы Прогнозирование и способы защиты населения и объектов.docx

well and install a deformograph. A deformograph is a sensitive device which reacts even the deformation caused by earth tides. Earth tides are mass movements of the crust.

Some data can be obtained even from rocks. These data are called seismic waves. The speed of seismic waves before the earthquake is significantly reduced, but before the earthquake it returnes to normal value.

Geomagnetism, terrestrial electricity, radon content in groundwater, the water level in wells, changes of temperature, changes in the chemical composition of water and gas, and of course, the behavior of domestic and wild animals - all of these, especially in a complex, allow to predict the time and place of the next tragedy quit accurately.

Nowadays, Russia has developed more than 20 techniques and technologies for earthquake prediction. A network of seismic stations is created, but the huge size of the country requires a lot of material costs for monitoring many kilometers of earth surface, modernization and equipping with modern measurement and diagnostic equipment, the creation of new fixed and mobile ground-based, airborne and space-based monitoring systems.

Organization of continuous control over seismic situation includes seismic monitoring and forecasting of possible earthquakes.

There exist long-term, medium-term and short-term forecasts. Less controversial is the long-term one, which smoothly merges with the objectives of zoning. Observations of these processes can predict an earthquake for a period from several months up to several years.

The medium-term outlook, which gives an opportunity to get a warning about a seismic event weeks or months before, has practical concreteness. Formalized criteria for assessing the statistical significance for the precursors and complex are used. On the basis of mainly established practical relations between parameters and precursors of earthquakes, place and magnitude of the expected earthquake is estimated.

Advances in research of medium-term outlook are not big. As well as in case of the long-term forecast, experts can be proud of the concrete results, but this is rather an exception of the general rule.

The short-term outlook is a forecast with a lead time of several hours or

days.

Reliability of short-term outlook due to its great social significance must

be presented to the most stringent requirements. Particularly high is responsibility of scientists and officials at the announcement of "seismic alarm". To understand the complexity of the situation, let’s recall to the famous Chinese seismologists

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forecast. In 1975, Chinese scientists repeatedly announced alarm in the area of a relatively small city Haicheng and even carried out the evacuation of the population. Multiple alarms were false but they happened in the agricultural area and did not lead to significant economic losses. But one of the evacuations was carried out 2 hours before the 9 - magnitude earthquake and had helped to save thousands of lives. However, in the next year scientists decided not to announce the alarm in Tanshaneb fatalities.

The forecast includes both seismic zoning and identification of earthquake precursors.



Figure 2 - seismic zoning of Russia

Seismic zoning is the selection of areas in which we could expect an earthquake of a certain magnitude. Seismic zoning of different scales is carried out on the basis of considering such parameters, as geological, tectonic and others. Seismic zoning maps give information about the distribution of earthquakes in a

certain area. In the USSR, a seismic zoning map was first drawn by G.P. Gorshkov in 1936. Since then, this card has been refined and reprinted several times.

For the territory of Russia a set of new general seismic zoning maps for the Russian Federation (Ulomov VI, 2004) - SIR-97 A, B, C, is drafted. It was created by the Institute of Earth Physics with the participation of many other organizations of geological-geophysical and seismological profile. General seismic zoning in the scale (1: 8 000000) was first implemented for the entire territory of the Russian Federation, including the territory of the platform and shelves of marginal seas. This set of maps is included in the Building regulations - SNIP II-7-81 *

«Construction in seismic areas" and adopted in 2000 by the Russian State Construction Committee as regulations, the implementation is mandatory for all design and construction companies engaged into work on territory of the country [13]. The map shows the intensity of the seismic activity in points (6-10 points) for the average geological conditions, and the earthquake location. Maps characterize varying degrees of seismic hazard at three levels of probability - 90% (Map A), 95% (Map B), 99% (Map C): the probability of a possible excess of intensity for 50 years (SIR-97-A

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- 10%; SIR-97-B - 5%; SIR-97-C - 1%). Time is not expected.

New maps SRF-97 for the first time made it possible to quantify the degree of seismic risk for specific construction projects. Map of SIR-97-A, corresponding to the 500-year period of the seismic impacts, is recommended for use in large- scale construction (this risk is acceptable in most countries). Maps SIR-97 SIR-B and 97-C, corresponding to 1000- and 5000-year return period concussions, are intended for use in the design and construction of the increased responsibility of objects and especially important objects.

For the competent anti-seismic design of building in earthquake-prone areas, scientists create maps of a larger scale, which is called seismic microzoning. Their purpose is specification of seismic intensity area, taking into account particular geological conditions. It is necessary for competent designers to create anti-seismic construction, for the correct choice of the construction site, such as foundations, special design measures.

There are a large variety of earthquake precursors, starting from the actual geophysical and ending with hydrodynamic and geochemical methods.

Other harbingers of earthquakes could be the rapid growth rate of weak shocks (foreshocks), crustal deformation, caught by laser light sources from space satellites, the radon content of the water, changes in groundwater level variations, etc. Indirect signs of a strong earthquake should be known to everyone who lives in earthquake-prone areas:

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  sharp changes of water levels in reservoirs and wells;
  
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  changes of water temperature in reservoirs and its blurred;
  
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  bright flashes of light poles, glowing orbs, lightning, reddish glow in the clouds and the earth;
  
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  unusual odors (radon gas);
  
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  a few hours before the earthquake set the extraordinary silence;
  
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  irregularities in the radio, TV, electromagnetic devices, a compass;
  
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  spontaneous glow of fluorescent lamps;
  
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  unusual behavior of animals.
  

Recognization of these signs in time means guaranteed salvation. Residents of the earthquake-prone areas should always be prepared to unpleasant surprises of nature. The best defense against them are solid buildings, and strict observance of Earthquake Engineering.

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Earthquake precursors

Following the changes in the various Earth parameters, seismologists hope to establish a correlation between these changes and the occurrence of earthquakes. Those characteristics of the Earth whose values change regularly before earthquakes are called harbingers, and deviation from normal values are called abnormalities.

The main precursors of earthquakes which are currently studied are the following.

Seismicity. The position and the number of different earthquakes magnitudes can be an important indicator of impending a strong earthquake. For example, a strong earthquake is often preceded by a swarm of weak shocks. Detection and enumeration of earthquakes requires a large number of geophones and associated data processing devices.

Movement of the Earth's crust. Geophysical network using triangulation network on the surface of the Earth or the observations from space by satellites to detect a large-scale deformation (change in shape) of the Earth's surface.

Lowering and raising of the earth's crust. Vertical movement of the Earth's surface can be measured by precise leveling on land or sea-level gauges in the sea.

The slopes of the earth's surface. For the measurement of the earth's surface inclination an instrument called inclinometer was designed.

Warp. To measure the deformations of rocks, wellbores are drilled; the deformograph is installed inside, which registers the value of the relative displacement of two points.

Seismic velocity. The speed of seismic waves depends on the stress state of rock through which the waves travel.

Geomagnetism. The Earth's magnetic field may experience local changes due to rock deformation and crustal movements. In order to measure small variations in the magnetic field special magnetometers were developed .

Terrestrial electricity. Changes in the electrical resistance of rocks may be associated with the earthquake.

The concentration of radon in groundwater. Radon is a radioactive gas which can be found in the groundwater and in water wells. It is constantly released into the atmosphere of Earth.

The water level in wells and boreholes. Groundwater level before earthquakes often rises or falls as it was in Haicheng (China) due to changes in the stress state of rock.

Changing of the temperature of near-surface layers of the earth. Infrared shooting from outer space orbit allows to recognize a thermal blanket of our planet which is generated near the surface of its thermal radiation.

Animal behavior. For centuries, extraordinary animals behavior before the earthquake have been reported, although until recently

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this message always appeared after the earthquake, but not before it [13].

3. Earthquake Prediction Methods

Modern earthquake prediction models are built on the basis of a comparison of experience and the results of laboratory simulation against field seismic observations.

Model avalanche-unstable fracture (AUF)

The model was created by experts of the Institute "Physics of the Earth" [14]. The essence of the model is, that various stages of cracking are followed by changes in the deformation rate inside and outside the fault zonet, which inevitably leads to changes in the physical properties of the medium.

Dilatant - Diffusion (DD) model

Model DD is developed by American scientists. Recently, this model was supplemented with quantitative estimates. Considering the option of so-called soft switching, George Rice showed that the condition of dynamic (seismic) instability in the real rock mass is delayed because of changes of interstitial pressure and start of liquid filtering.

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