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EARTHQUAKES & SEISMIC WAVESPowerPoint Presentation

EARTHQUAKES & SEISMIC WAVES

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### EARTHQUAKES & SEISMIC WAVES

CHAPTER 6.2

What is an earthquake?

- The shaking and trembling that results from the movement of rock beneath Earth’s surface
- Caused by plate movement

Where does an earthquake start?

- Focus: area beneath Earth’s surface where rock that is under stress breaks, triggering an earthquake
- Epicenter: point on the surface directly above the focus

How does an earthquake move?

- Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

p waves

- First waves to arrive
- Compress and expand the ground like an accordion
- Crust vibrates forward and back along the path of the wave
- Can damage buildings
- Travels through solids and liquids

S WAVES

- Secondary waves
- Seismic waves that vibrate from side to side as well as up and down
- Cannot travel through liquids
- Shakes structures violently

Moves like ‘the wave’ at a football game

SURFACE WAVES

- Move more slowly than P waves and S waves, but can produce severe ground movements
- Can make the ground roll like ocean waves or shake buildings from side to side

How are seismic waves measured?

With a SEISMOGRAPH

What are the 3 ways to measure an earthquake?

- 1. Mercalli scale: rates the earthquakes according to level of damage at a given place (pg 191)

Mercalli Scale XII in La Paz, Bolivia

- 2. Richter Scale: rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves
- Magnitude of an
Earthquake: a # that

geologist assign to

an earthquake based

on the earthquake’s size

- 3 based on the size of the earthquake’s seismic waves. Moment Magnitude Scale: rating system that estimates the total energy released by an earthquake

Geologists use the seismic waves to locate based on the size of the earthquake’s seismic wavesan earthquake….

EPICENTER

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