An earthquake is caused by a sudden slip on a fault (断层). A fault is a fracture in the crust (地壳) of the earth along which rocks on one side have moved relative to those on the other side. Stresses in the earth’s outer layer push the sides of the fault together, build up, and then the rocks slips suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake.
Earthquakes tend to be concentrated in narrow zones. There are 7 major crystal plates on earth, about 80 km thick, all in constant motion relative to one another. They move at a rate of between 10 and 130 mm per year.
It is estimated that there are several million earthquakes in the world each year. Many of these earthquakes go undetected because they occur in remote areas or have very small magnitudes (震级). The USGS Earthquake Information Centre locates 12, 000 to 14,000 earthquakes each year (about 35 per day). On average, about 60 earthquakes p
A. how earthquakes are formed and classified
B. how earthquakes can be predicted and located
C. earthquakes do not so often occur on the earth
D. earthquakes are considered to be a threat to humans
An earthquake is caused by a sudden slip on a fault (断层). A fault is a fracture in the crust (地壳) of the earth along which rocks on one side have moved relative to those on the other side. Stresses in the earth’s outer layer push the sides of the fault together, build up, and then the rocks slips suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake.
Earthquakes tend to be concentrated in narrow zones. There are 7 major crystal plates on earth, about 80 km thick, all in constant motion relative to one another. They move at a rate of between 10 and 130 mm per year.
It is estimated that there are several million earthquakes in the world each year. Many of these earthquakes go undetected because they occur in remote areas or have very small magnitudes (震级). The USGS Earthquake Information Centre locates 12, 000 to 14,000 earthquakes each year (about 35 per day). On average, about 60 earthquakes p
A. Earthquakes of large magnitudes cause casualties.
B. Earthquakes often happen in narrow zones.
C. Earthquakes involve the release of energy.
D. Earthquakes can cause waves in the sea.
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