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 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 3 Types: Primary (P) waves Secondary (S) waves Seismic Waves—A type of vibration that travels through the Earth 3 Types: Primary (P) waves Secondary (S) waves 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

Average occurring annually 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