Earthquake book

Written by Seyoung Choi

Index

• What causes earthquakes?--------3• Where do earthquakes occur?---------4• Pictures about slide 4---------------5• What are faults?-------------------------6• Pictures about slide 6------------------7• What are seismic waves?--------------8• Pictures about slide 8--------------------9• How are earthquakes measured?-------10• Pictures about slide 10----------------11• What are some of largest ever earthquakes

recorded in history?----------------------12

What causes earthquakes?

Why do you think earthquakes happen? There should be a reason why the earth’s surface moves. I’ll explain why earthquake happens in this page.

What causes earthquakes? Earthquake happens because of the plate’s movement. The earth’s litho-

sphere is divided into many plates and they move. The convection currents from the mantle and outer core makes the earth’s plates move. There are three types of the plates’ movement called stress, and they are tension, compression and shearing.

What is tension? Tension is the type of movement that two plates pulls apart. What is compression?Compression is another type of movement that two plates pushes together.What is shearing?It is the type of movement that two plates slip apart and it can change earth’s

surface.

Where do earthquakes oc-cur?

Where do earthquakes occur? Think about California or Japan. Earthquakes frequently happen in some countries, but there are the countries that there are almost no earth-quakes. Why do you think that happens? It is because of the place where that country is. If you think about Japan, Japan is in the middle of Eurasian plate, Phillippine plate and Pacific plate. The place between two plates is called plate boundaries, and the earthquake occurs in the plate boundary.

What are faults? What do you think fault is? Do you think it is responsibility for wrongful act? It’s not it for the

earthquake. The faults are the break of the earth’s surface where they slip past each other. After the stress builds up enough, the surface breaks and that is fault. The both sides of the surface can move up, down or sideways. There are three types of faults. They are normal faults, reverse faults, and strike-slip faults. Most of the faults occur along the plate bound-aries.

What are normal faults? Tension of the crust pulls the rocks apart, and that is called Normal faults. One block of rock

lies above the fault and the other block of rock lies below the fault in normal faults because the fault is at an angle. The block of rock that lies above the faults is called Hanging wall and the rock that lies below that fault is called Footwall.

What are reverse faults? Reverse fault is one of the fault that two parts of the rock pushes together. It is same struc-

ture as normal faults but the blocks move in the opposite direction. Hanging wall lies above the fault and the footwall lies below the faults like normal faults. Northern Rocky mountain is one of the example of reverse fault.

What are strike–slip faults? Sometimes, plates move past each other, and that is called strike-slip fault. In strike-slip

faults, both of the side of the fault slip past each other in side-ways and it moves little up or down. The transform boundary is the strike-slip fault that forms the boundary between two plates.

Click here to look at the figure.

Normal fault Reverse fault Strike-slip fault

What are seismic waves? Seismic waves are the vibrations of the earthquake that spread out from

the epicenter. There are three kinds of seismic waves which are P waves(primary waves), S waves(secondary waves), and surface waves.

• What are P waves? When earthquake happens, you can feel earth’s surface is shacking. It is

because of the seismic waves and P waves(primary waves) is one of the seismic waves. Like its name, P waves come first when earthquake hap-pens. P waves move like accordion, back and forth. It can damage build-ings.

• What are S waves? Next, S waves come. S waves draw S shapes when it moves thorough the

surface. It is stronger than P waves but it can’t move thorough liquids.• What are surface waves? Surface waves are slower than P and S waves but it can it can change the

shape of earth’s surface and it is strongest.• Slinky can be a good object to understand the seismic waves. You can

move it forward and back like accordion to make P waves and you can make S shape to make S waves.

Click here to look at the figure.

Surface waves change earth’s surface.

P waves damage buildings.

neophobic.ro

How are earthquakes measured? Many people wants to know how big was that earthquake after the earthquake happens.

Therefore scientists measure earthquakes. In this page I’ll explain you about how scien-tists measure earthquakes.

How many ways are there to measure earthquakes and what are they? There are a lot of ways to measure earthquakes, at least 20 ways. But, scientists com-

monly use three ways, and they are Mercalli scale, Richter scale, and Moment magnitude scale.

What is Mercalli scale? The Mercalli scale rates earthquake by how much damage it caused. There are levels 1 to

12. There is more damage in the place near by epicenter, and there’s less damage in the

place far away from epicenter. Epicenter is the focus where earthquake starts.

What is Richter scale? The Richter scale measures seismic waves with the seismograph. Seismograph can feel

really small movement that people can’t feel. It is more accurate for small and nearby earthquakes than far and big earthquakes. Scientists mostly use Richter scale.

What is moment magnitude scale? Scientists today mostly use moment magnitude scale to measure earthquake because it is

most accurate. It can measure either small or big, near or far earthquakes.

Click here to look at the figure.

This is how Mercalli scale works.There’s more damage in the place nearby epicenter and there’s less damage in the place far from epicenter.There are scales 1 to 12.

Richter scaleThis is seismograph, and it records movement.

What are some of the largest ever earthquakes recorded in history?

The largest ever earthquakerecorded in history

The largest earthquake recorded in history happened in 1960 in

Chile magnitude 9.5. The epicenter was about 100

miles off the coast of Chile under the pacific ocean. The towns nearby Chile were also suffered by the earthquake. After the earthquake happened in Chile and nearby towns, the earthquake moved thousands of mile thorough Pacific ocean and reached Hawaii, tsunami happened there.

Some of the big earthquakesIn September 7th, 1999, one of the big earthquakes happened in Athens, Greece. Almost 7,000 house destroyed and 100,000 people lost their house and lived in the tent.

In August 1st, 1999, magnitude 7.4 earthquake happened in Izmit, Turkey. Hundreds of buildings de-stroyed and at least 15,000 peo-ple died.

Resources

• Ms. Corfield’s website(helpful web-sites)

• Science CD(Science book)• Internet