What is an Earthquake? Goal  Homework  Demonstrate the different motion of P and S-waves 1.Earthquake Vocab defined Warm-up Take out last night’s HW, Update TOC, copy down HW In your journal  Write a brief paragraph that explains in general terms what an earthquake really is. Include the words “plate boundary,” “fault,” and “elastic rebound” in your definition.

What are Earthquakes? The shaking or trembling caused by the sudden release of energy Usually associated with faulting or breaking of rocks Continuing adjustment of position results in aftershocks Near plate boundaries, there are many breaks in the rock called faults. Over time, as the plates gradually get pushed along, more and more pressure builds up at the faults. Elastic rebound occurs when a fault can’t take any more pressure and snaps. We experience this motion as an earthquake.

Earthquakes Seismology  Seismologist  study of earthquakes scientist who studies earthquakes and seismic waves Keep in mind: Seismologists don’t have to be right near an earthquake to study it. Why is this? Real-time Data: World Earthquake Map

Earthquake Vocabulary Fault  Deformation  a break in the crust along which plates shift and slip past each other rocks changing shape due to stress from tectonic motion Sometimes, rock layers just gradually crunch together and bend.

Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur near the Pacific Ocean (Ring of Fire) most of these result from convergent activity more than 150,000 quakes strong enough to be felt are recorded each year

BREAK Earthquake Vocabulary Elastic rebound  But if something can’t bend, then it will probably… BREAK Elastic rebound  stress builds up to the point where the rock breaks and snaps back

What is the Elastic Rebound? Explains how energy is stored in rocks Rocks bend until the strength of the rock is exceeded Rupture occurs and the rocks quickly rebound to an undeformed shape Energy is released in waves that radiate outward from the fault

Elastic Rebound Elastic Rebound To view this animation, click “View” and then “Slide Show” on the top navigation bar. Animation

At your table, take one minute to discuss the following: Seismic Waves At your table, take one minute to discuss the following: What are seismic waves? How do they tell us about the interior of the Earth?

Seismic Waves Seismic waves  Earthquake vibrations that travel through the Earth. Different types of seismic waves travel through the Earth’s layers at different speeds.

Seismic Waves When an earthquake occurs, seismic waves are shot out in all directions: Some travel across the Earth’s surface (surface waves) Some travel through the Earth (body waves) P-waves S-waves

What is a Seismograph? Seismographs To view this animation, click “View” and then “Slide Show” on the top navigation bar. Animation

What property determines the speed at which seismic waves travel? Surface wave Density of the rock

Seismic waves travel best through MORE / LESS dense rock layers. In other words, the vibrations unleashed by earthquakes travel best through… dense, solid rock. Surface wave

P and S-Waves Both can be easily demonstrated with a Slinky!

Is any domino actually traveling along with the wave? Seismic Waves motion of wave Is any domino actually traveling along with the wave? Picture the molecules within the rock to be like dominoes knocking into each other.

Seismic Wave Motion with Surface Effects Effects of Seismic Waves Seismic Wave Motion with Surface Effects To view this animation, click “View” and then “Slide Show” on the top navigation bar. Animation

Seismic Waves Seismic waves are like sound waves. They travel best through solids materials.

through the entire earth slowest, but most damaging Seismic Waves P-waves S-waves L-waves Full name Where they travel Relative speed Type of motion primary waves Secondary waves surface waves (lateral) through the entire earth only through solid on the earth’s surface slowest, but most damaging fastest slower up, down, and around in and out side to side

Earthquake Measurement Section 5.2: Earthquake Measurement Seismogram (printout of seismic waves) Seismograph (measuring instrument) P-waves first then S-waves How do scientists find an earthquake’s start time? By comparing the arrival times of P and S-waves.

Earthquake Epicenter: Focus  Epicenter  Actual point of the shift along the fault (usually miles underground) Closest point to the focus on the earth’s surface (always directly above the focus)

What is an Epicenter? A point on the surface of the Earth directly above the FOCUS of the earthquake. The point within the Earth from which earthquake waves originate.

Locating the Epicenter:

Earthquake Epicenter: What does the red line in the graph represent? What does the purple line represent? Which location is the farthest away from the earthquake’s epicenter? time/distance of S-waves time/distance of P-waves station C

Earthquake Epicenter: 4. What is the S-P time interval (ΔT) for location C? 5. Which location is the closest to the earthquake’s epicenter? 6. How far is station A from the epicenter? 23 – 12 = 11 minutes station A ~1,700 km

Earthquake Strength 10 10 10 100 4  5  6  7 x 10 x 10 x 10 = What is the measure of the strength of an earthquake called? Magnitude Richter scale  Based on a factor of _____ for each level. A magnitude 3 is ____ times as strong as a magnitude 2. A magnitude 4 is ____ times as strong as a magnitude 3. A magnitude 4 is _____ times as strong as a magnitude 2. How much stronger is a magnitude 7 than a magnitude 4? measures the strength of the ground motion 10 10 10 100 4  5  6  7 x 10 x 10 x 10 = 1,000 times stronger

Earthquake Strength and Intensity Haiti earthquake What is the difference between this scale and the Modified Mercalli Intensity Scale (MMIS)? List of greatest magnitude earthquakes

Earthquake Damage Tokyo, Japan: 1923

Earthquake Damage Japan: 2004 Magnitude = 6.6

Earthquake Damage New Zealand: 2010 Magnitude = 7.1

Earthquake Damage Mexico: 2010

Earthquake Damage Oakland, CA: 2007

Earthquake Damage Canterbury, England: 2010 Magnitude = 7.1

Earthquake Damage Anchorage, Alaska: 1964

Earthquake Damage Alaska: 1964

You and your partner are now going to practice locating an epicenter through this Power Point. First you will practice finding Lag Times (the time difference between when P-Waves and S-Waves arrive at recording stations). Second you will use your Lag Times to find the distance from the station to the epicenter

Use the data from the recording stations: Station A: San Francisco, California P-Wave arrival 3:02:20 S-Wave arrival 3:06:30 What is the time difference between P and S wave arrivals? 4:10

Use the data from the recording stations: Station B: Denver, Colorado P-Wave arrival 3:01:40 S-Wave arrival 3:05:00 What is the time difference between P and S wave arrivals? 3:20

Use the data from the recording stations: Station C: Missoula, Montana P-Wave arrival 3:01:00 S-Wave arrival 3:03:00 What is the time difference between P and S wave arrivals? 2:00

Difference in arrival times (LAG TIME): San Francisco: 4:10 min. 2,800km Denver, Colorado: 3:20 min. 2,000km Missoula, Montana: 2:00 min. 1,100km

You may have used these is math before! This is a compass… You may have used these is math before! We will be using a compass to draw a circle where the radius of the circle equals the distance from the seismograph to the epicenter.

Using the distance from the station to the epicenter: San Francisco: 4:10 =2,800km Open your compass to the EXACT distance on the scale. 1,000 2,000 3,000 4,000 5,000

. . . Use your carefully set compass to draw a circle around each city. . 1,100km . . 2,800km 2,000km You've found the epicenter!