Earthquakes Where do Earthquakes occur 28Lithosphere What causes

Earthquakes

Where do Earthquakes occur? • 28)Lithosphere

What causes Earthquakes? • Earthquakes occur where tectonic plates are moving. • They can move towards each other, away from each other, or horizontally beside each other.

#29 Geologists analyze earthquake waves (seismic waves) to determine the composition of the layers within Earth.

Transform – San Andreas Fault

What would you do? • 39) If you were inside a building, the best thing to do when an earthquake occurs is immediately hide under a desk or chair. • Something strong to cover your body.

What would you do? • If you are outside when an earthquake begins, you should? Run away from buildings!!!!!

• A seismograph is a machine that measures earthquakes.

• A seismogram is a tracing of earthquake motion created by a seismograph.

Earthquake: Epicenter & Focus - The location where the earthquake begins and rocks being moving. The ground ruptures at this spot, then seismic waves radiate outward in all directions. Epicenter - The point on the Earth's surface located directly above the focus of an earthquake.

Epicenter & Focus

Waves and Energy Seismic Waves—A type of vibration that travels through the Earth 3 Types: 1. Primary (P) waves 2. Secondary (S) waves 3. Surface waves

Primary (P) waves • Fastest waves!!! • Travel through solids, liquids, and gases • A type of seismic wave that compresses and expands the ground. • The first wave to arrive at an earthquake. • Least Destructive

Surface waves • Move along Earth’s surface, not inside! • Travel slowest! • Most destructive

Secondary (S) waves • Slower than P waves • Pass through solids only (can’t move through liquid outer core) • A type of seismic wave that moves the ground up and down or side to side

Comparing P & S Waves

Remember difference between waves? • P wave is the fastest wave and least destructive! • The Surface wave is the slowest wave and the most destructive. • S wave is not the fastest or slowest, it is in the middle!

Shadow zone • 36)A shadow zone is formed on the opposite side of the Earth from where the earthquake occurred because S waves are blocked by liquid.

Tsunami

How often does an earthquake occur measuring 7. 2 on the Richter scale, based on the information below? How often does an earthquake measuring 3. 3 occur on the Richter scale? Descriptor Magnitude Average occurring annually Great 8. 0 and higher 1 Major 7. 0– 7. 9 18 Strong 6. 0– 6. 9 120 Moderate 5. 0– 5. 9 800 Light 4. 0– 4. 9 about 6, 200 Minor 3. 0– 3. 9 about 49, 000 Very minor 2. 0– 2. 9 about 365, 000

Why do Scientists KNOW the Earth has a liquid layer? #35 S waves are blocked by liquid. Since seismographs on the opposite side of the Earth do not receive any S waves after an earth quake so scientists have concluded that the Earth has a liquid layer

Earthquake Magnitude using Richter Scale Measures earthquakes using a scale of 1 -10. Moves up 1 number = an increase of almost 32 times more energy • Example: magnitude 5 earthquake = almost 32 times more energy than a magnitude 4

How are Earthquakes Measured? Richter Scale