Good morning everyone, I am Jialin Yin. Today, I want to talk about the earthquake. In 2008 May 12th, it was the first time that I felt the earthquake which was a 7.8-magnitude earthquake happened in Wenchuan China. At that time, I was a 7th grade student and sit in class room, then, I noticed that the light on the ceiling began to shake slightly. Then, the broadcast news reminds me, that was an earthquake and approximately 70000 people died in this severe natural disaster.
During the speech, I will explain the earthquake in geographic view to you. Firstly, for what reason caused the earthquake? Generally, when rocks experience brittle failure, a kind of energy called seismic waves are released from the point of breakage. The seismic waves generated cause the ground shake, creating an earthquake. That point of breakage is called the focus, or hypocenter of the earthquake. A term people might be generally familiar with is epicenter which is the point on the surface of Earth directly above the focus, and the focus is the true center of an earthquake.
Secondly, I want to talk about where are earthquake located, the first picture is the plate boundary. You can observe that there are many red dots on the second picture. These red dots represent epicenter of earthquakes that have occurred over the past 50 year. Actually, what you can notice right away is that most of these earthquakes occurred along with the plate boundaries. Moreover, we can also notice is that there are a few earthquakes that occur far away from plate boundaries, these kinds of earthquakes named intra-plate earthquakes. About only five percent of earthquakes that occur each year are intra-plate earthquakes.
Look at this chart, here are five columns, they are magnitudes, frequency, description, example and energy release. In fact, from earthquake magnitude 2 to 6, the energy release and damage is not huge. The classes of seismic measure for the modern buildings are 5 to 6. However, if the earthquake magnitude is bigger than 6, the energy release can be destructive even billions dollar loss of life. Let us specify the damage of magnitude 8 and 9. The difference of energy from one magnitude to another is approximately 31 times.