Earthquakes!

Think! What are important characteristics to have in building an earthquake safe building?

What are the focus & epicenter?

Types of Faults

How can earthquakes change Earth’s surface?

San Andreas Fault

• 1300km (807mi) through CA and into the Pacific Ocean

• 1906 San Francisco EarthquakeLand on the western side of the fault moved 4.7 meters relative to land on eastern side

Causes of Earthquakes• Elastic Rebound—rapid release of energy stored in rock that has been subjected to great force

•Energy is released as seismic waves

• deformed rock along fault springs back

•Think about what happens to elastic rubber band

Aftershocks & Foreshocks•What is an aftershock?• Occur after major earthquake• Can be hours to weeks after• Usually much smaller but can still damage

•What is a foreshock?• Small earthquakes that come before major earthquake• Can happen days or years before

Think! What might cause aftershocks & foreshocks?

Math & Earthquakes Think!

In 25 years, how much movement will result from a fault that slowly slips 1.5cm/year?

Answer: 37.5cm

Types of Seismic Waves•Body waves travel through Earth’s interior—P & S waves

•Surface waves produced when body waves reach surface—Love & Rayleigh • Most destructive• Larger than body waves

•P waves=push-pull waves

•S waves=shake waves

Recording Seismic Waves•Seismographs—record seismic waves• https://www.youtube.com/watch?v=Gbd1FcuLJLQ

•Seismogram—time record of ground motion• Shows all 3 types of waves• Stronger the earthquake=larger the wave on the seismogram

Measuring Earthquakes•Richter Scale & Moment Magnitude measure earthquake magnitude • Magnitude=measure of size of seismic wave or the amount of energy released

at the source of the earthquake

•Modified Mercalli Scale• Earthquake’s intensity

Difference Between Magnitude & Intensity?•Intensity—severity of shaking & damage

•Magnitude—amount of energy released

Intensity

Magnitude

How to Find Epicenter• Look at data from 3 different stations

• At each station look at:• A. What time the first P wave came• B. What time the first S wave came• C. Determine how many minutes were between the two waves• D. Look at graph and figure out how far away the epicenter is from that station

•Compare data from the 3 stations• A. For station 1 draw a circle around the station with a radius the distance from the station• B. Repeat for station 2 & 3• C. The location where the 3 intersect is the epicenter

• What is the difference in arrival times between P waves & S waves for a seismic station that is 2000km from an epicenter?

• How far away is the epicenter of an earthquake when there is a 2 minute time lapse between P & S waves?

• Determine the distance between an earthquake and seismic station if the first S wave arrives 4 minutes after the first P wave.

• THINK! Write your own word problem using the graph.

Causes of Earthquake Damage•Seismic Shaking—ground vibrations

•Liquefaction—soil & rock saturated with water becomes weaker

•Landslides & mudflows

•Tsunamis https://www.youtube.com/watch?v=w3AdFjklR50

Reducing Earthquake Damage•Assessing earthquake risk• Does California have a high or low risk? Why?

•Seismic gap—area along fault where there has not been any earthquake activity for long period of time

•Seismic-safe designs

•Earthquake safety

Earth’s Layered Structure

Crust• Oceanic• 7km thick• Basalt and gabbro• 3.0g/cm3 density• 180million years old or less

•Continental• 8-75km thick• Granitic rock called granodiorite • 2.7g/cm3 density• 4billion years old

Mantle• 82% of Earth’s volume

• solid, rocky shell

•Peridotite

•Density about 3.4g/cm3

Core• iron-nickel alloy

• 13g/cm3

•Outer core—liquid layer, generates earth’s magnetic field

•Inner core—compressed into a solid by great pressure

Lithosphere, Athenosphere, & Lower Mantle• Lithosphere—crust & uppermost mantle, 100km thick

•Athenosphere—beneath lithosphere

•Lithosphere & Athenosphere are both part of the upper mantle, weaker layer

•Lower Mantle—660km down to the base of the mantle, rigid layer