Earthquakes

Warm-up

What are earthquakes in your

words?

Why Earthquakes Happen

Earthquakes are the vibrations of energy (called seismic waves) produced from the breaking rocks.

Caused by the movements of the plates and where rocks cannot undergo any greater stress.

Stress Stress is a force that makes rocks

change their shape or volumes.

Squeezes rocks together

Stretches rocks apart

Pushes rocks in different directions

Rocks will bend until their elastic limit is met and then they break at faults.

Faults vs. Folds

Faults – places where rocks break

Folds – rocks bend but do not break

Three Types of Faults

Normal – rocks get stretched apart

Reverse – when rocks get compressed

Strike-Slip – when rocks slide past each other with no up or down movement

Seismic Waves

Waves produced by an earthquake.Focus – place in the Earth where

the Earthquakes startEpicenter – place on the Earth

surface directly above the focus

Earthquake Waves• travel out in all

directions from the focus

• Epicenter: point on Earth’s surface directly above the focus

3 Types of Waves

Primary (P-waves) – front to back. Fastest type

Secondary (S-waves) – up and down. Second fastest

Surface waves (L- waves) – backwards rolling and side to side swaying. Slowest but cause the most damage.

http://www.pbs.org/wnet/savageearth/earthquakes/index.html

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization

Structure of Earth

Primary waves travel through solids and liquids so they pass through to the other side of the Earth

Secondary waves only travel through solids NOT liquids so they stop at the outer core This is how we know the outer core is liquid

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1009/es1009page01.cfm?chapter_no=visualization

Changes in Speeds

Waves speed up from crust to the upper mantle at the Mohorovic Discontinuity

Slow in the Asthenosphere

Speed up once waves reach the lower mantle

S-waves stop at the outer core but P-waves continue then speed up in the inner core

Measuring Magnitude

Magnitude – measure of the energy released Richter scale – for every 1.0 higher on scale

the earthquake is 32 times stronger Modified Mercalli – based on structural

damage done by the earthquake

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1005/es1005page01.cfm?chapter_no=visualization

Tsunamis

Giant waves of water produced after earthquakes occur

Warning Signs: Recent earthquakes

Water on the shore is sucked back into the ocean exposing the land underneath

http://www.pbs.org/wgbh/nova/tsunami/anatomy.html