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Earthquakes are happening every day and as we speak, that's why it's very important to be prepared for earthquakes. Los Angeles and San Francisco really need to be careful, because earthquakes occur many times there. If you want to find out more information, read on.
Causes
There are many causes of earthquakes, but almost all of them are caused by changes in the earth's structure. Many of the earthquakes happen where there are faults in the earth's surface. A fracture occurs, and there is a release of energy in the form of vibration. The main cause of an earthquake is usually a sudden break in rocks that have been changed by great pressure. Some are caused by the activity of a volcano.
Types or Categories
There are 4 types of seismic waves. They are, the P wave, S wave, Love wave and Rayleigh wave. The P wave stands for primary waves, and the S wave stands for secondary waves. The first wave that arrives during an earthquake is the P wave. P waves push together and pull apart the rocks in the ground. S waves move more slowly than P waves. As S waves go through the ground, they move the layers of rocks up and down and side to side. Love waves are also known as surface waves, and follow P waves and S waves. Surface waves only affect the Earth's surface. Love waves make the surface move side to side like a snake. There is a second type of surface wave, it is the Rayleigh waves. This wave causes the ground to rise and then fall like the surface of the ocean when large waves pass by.
Locations
There are two major areas where earthquakes occur. The first is the Circum-Pacific belt which goes all the way around the Pacific Ocean. The second goes through Europe and Asia and is called the Alpide belt. As you already know earthquakes occur many times in California.
Frequency
In California, there will be major earthquakes about every 130 years. This number is only an average. Earthquakes have happened in as few as 45 years or as many as 300 years. For all earthquakes, the frequency depends on the slipping rate of the plates. There may be as many as 1,000,000 earthquakes on our planet each year.
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