Unit 3: The Dynamic Earth

Earthquakes, Earth’s Interior and Geologic Hazards

What is an earthquake?

•Shaking of the earth’s crust due to a release of energy/pressure along a fault line

•Fault: crack in the earth’s crust where there is movement

What do earthquakes result from?

•Movement along a plate boundary•Volcanic eruptions

•Plate: section of the earth’s crust or lithosphere which moves-includes oceanic and continental crust (either, or both)

Elastic rebound theory

•Explains movement•Says: strain builds up between 2 sections

of crust, deforms them. When the stress overcomes friction, crust shifts and goes back to its original shape ( in new place).

Earthquake Anatomy

focus

Focus: point of originOf EQ underground

Epicenter: where the EQOriginates on the surface

Seismic waves: how energy travels through theEarth from the EQ

How do we measure Earthquake strength or magnitude?•Richter Scale- based on powers of ten (log

scale), calculated from amplitude of highest S-Wave on seismogram

•Measures from 1-10•1=1•2=10x more powerful•3=100x more powerfulHow powerful would a magnitude 5

earthquake be then a magnitude 1? Then a 4?

Answer: 10,000 and 10x

How do we measure Earthquake Intensity?•Modified Mercalli Scale- based upon

peoples observations, ranges from 1-12

Seismic Waves:

•Three types: P,S,L•P wave: primary, compress ional, body

wave, travels through solid, liquids, and gases

•S-Wave: Secondary, Shear, Transverse, body wave, travels through Solids only

•L-wave: Longitudinal, surface wave, (p/s wave converts to this when reaches the surface), two types-Love and Rayleigh Wave

Diagram of Body Waves:

Diagram of a Surface Wave:

Earth’s InteriorDo Now: Copy diagram and label

What is it like inside the Earth?•Dense•Hot•Solid or liquid depending on the layer•SEE ESRT page 10•Outer core is a liquid,• Inner core is a solid

How do we know about the earth’s interior?•From earthquake data•From meteorites•Remember- P waves can travel through everything,

S-waves can travel through solids only•Creates a Shadow Zone- 102° to 143° away from the

epicenter•The speed of the seismic waves depends on the

density of the material- more dense, faster waves•The Moho was discovered this way…

http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Shadow+Zone+Flash+Animation&flash_file=shadowzone&flash_width=220&flash_height=300

Why is there a Shadow Zone?•Earth’s outer core is a liquid and seismic waves

cannot travel through this zone.•P-waves are refracted and S-waves cannot travel

through this at all.

Ring of Fire

Ring of Fire

•Earthquakes and volcanoes are not distributed randomly- they occur in specific regions- usually along a zone where plate boundaries meet

•Ring of Fire-zone along the Pacific Ocean that rings it, where earthquakes and volcanoes are the most common/active

Seismic hazards

•Tsunamis: giant wave generated by a slip in the earth’s surface and thus an earthquake http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072402466/30425/16_19.swf::Fig.%2016.19%20-%20Formation%20of%20a%20Tsunami

•Building collapse, fires, water main breaks, gas main breaks result

•Liquifaction-occurs when ground saturated with water actually flows like a liquid with intense shaking, occurs with loose sediment

Volcanic Hazards

•Lava, ash is deadly•Mudflows or larhars are deadly•Toxic gases•Pyroclastic bombs, explosions are deadly•Cause acid rain•Landslides•Even though violent, lead to fertile soil

Seismic Risk Map (USA)