5. 12 blackboard newspaper for earthquake prevention and disaster reduction

5. 12 Selected photos of earthquake prevention and disaster reduction blackboard newspaper 0 1

5. 12 Selected photos of earthquake prevention and disaster reduction blackboard newspaper 02

5. 12 photo selection of earthquake prevention and disaster reduction blackboard newspaper 03 publicity knowledge of earthquake prevention and disaster reduction

Earthquake is a common natural phenomenon. According to statistics, there are about 5 million earthquakes on the earth every year, of which more than 50,000 are felt earthquakes and only a dozen are destructive earthquakes of magnitude 7 or above. How did the earthquake happen? This should start with the structure of the earth.

The earth is an elliptical sphere in motion. It is like a boiled egg, which can be roughly divided into shell, protein and yolk. The layer of the earth's surface equivalent to the eggshell is called the crust; The part below the earth's crust equivalent to the protein is called the mantle; The part below the mantle that is equivalent to the yolk is called the inner core. The crust is composed of rock layers, the upper layer is hard granite layer, and the lower layer is harder basalt layer. The average thickness of the earth's crust is about thirty or forty kilometers. The mantle is a molten material under high temperature and high pressure, with a thickness of about 2900 kilometers. The innermost part of the earth is a core with a radius of more than 3400 kilometers. It is estimated that the temperature is as high as 3000 to 5000 degrees Celsius, and the pressure inside the core is also amazing, which may reach several hundred thousand to two or three million atmospheres. While the earth is constantly moving, its internal substances are also moving slowly.

The rocks that make up the earth's crust are horizontal at first. The rotation of the earth itself, the constant movement of internal materials and the influence of celestial bodies have produced huge geostress in all layers of the crust, which has caused some strata to fold and deform. This change is long-term and slow, and people can't feel it. When the local stress is continuously accumulated and strengthened, and exceeds the strength of a certain stratum, the stratum there will suddenly rupture and move, and the long-term accumulated energy will be released sharply, and some of it will spread in all directions in the form of seismic waves. When it reaches the ground, the ground will shake. This is an earthquake. This kind of earthquake is called. Tectonic earthquake? It happens the most times and does the greatest harm. In addition, there are volcanic eruptions? Volcanic earthquake? Small area caused by cave or goaf collapse? Falling earthquake? Wait a minute.

Hengshan county is located on the south extension line of the road show fault zone, namely Liuyang? Hengyang? The geological structure of Yongzhou active fault zone is complex, and there is a geological structure background of destructive earthquake. According to historical records, there were three earthquakes in 1630 and 163 1 * *, which occurred in1February 9851June 3 17 and June 65438, 2008 respectively.