1. Earthquakes

2. What is an Earthquake?
Earthquakes are a natural hazard caused by the sudden and rapid movement of a large volume of rock.
The shaking and destruction cause by earthquakes are the result of slippage along fracture’s in Earth’s crust called faults.

3. Continued The origin of an earthquake occurs at the focus.
The point at the surface directly above the focus is called the epicenter.
During earthquakes, a large amount of energy is released as heat and seismic waves- a form of elastic energy that causes vibrations.

5. What causes Earthquakes?
4 layers (inner, outer, mantle, crust)
Crust and top of mantle (puzzle like) slowly slide past one another- tectonic plates
Edges are plate boundaries
Made up of faults (Earthquakes occur at faults)
Edges get stuck while plates keep moving
Once plates move far enough apart, the edges unstick on one of the faults….

6. BAM! EARTHQUAKE!!

7. Measuring the strength of an earthquake
Every earthquake is given a number. This number describes the magnitude (strength) of the earthquake.
The Richter scale of magnitude is used to calculate the strength of an earthquake.

9. Measuring cont.
Seismographs are instruments that record the vibrations of the earth during an earthquake.
Seismographs are also important for locating an earthquake.

11. Why does the Earth Shake?
Faults are stuck, blocks keep moving
The energy that would normally cause blocks to slide past one another is being stored up
Once they unstick, all the energy stored up is released
Energy radiates in all directions creating seismic waves
Seismic waves shake the earth as they travel through it (like ripples in a pond)

12. Seismic Waves There are two main groups of seismic waves:
Surface waves- travel along the outer part of Earth.
Body waves- travel through Earth’s interior. They are divided into two types called P waves and S waves.

13. P Waves
Primary (P waves) are “push-pull” waves. They push and pull rocks in the direction the wave is traveling.
Fastest waves
Go through solids and liquids

14. S Waves
Secondary (S waves) “shake” the particles at right angles to their direction of travel.
Move in a side-to-side motion.
Slower than P waves.
(Slinky Demonstration)

15. Safety during an earthquake
DROP, COVER, AND HOLD ON!
-Drop under something sturdy, hold on, and protect your eyes by pressing your face against your arm.
-Stay indoors until the shaking stops.
-Stay away from windows.

16. Built strong
Instruments are installed in buildings, bridges and other large structures in earthquake-prone areas to measure their response to earthquakes.