Aim: What is an earthquake? Do now: In your notes, explain where most earthquakes occur and Why? Japan

Earthquakes - are vibrations in the crust caused by moving crustal plates. California

Focus - the origin (starting point) of the earthquake underground. B. Epicenter – the location on the surface directly above the focus.

II. Causes of Earthquakes the release of potential energy stored in rock. energy is released in all directions

A. Elastic Rebound Hypothesis - Deformation of rocks (stressing/bending) cause them to build up pressure (energy). - When they break, the stored energy is released which results in the vibrations.

III. Measuring Earthquakes Seismology – the study of earthquake waves (energy). Seismographs – instruments that record earthquake waves (energy). *Seismos = earthquake

Seismogram – a graph produced by recording the ground motion on a seismograph.

Creation of Seismogram

Richter Scale: Measures the magnitude (strength) of an earthquake from the seismogram.

IV. Types of Seismic Waves (earthquake waves) epicenter created at the start of the earthquake. What do you notice about the waves in the diagram? wave motion through Earth helps scientists theorize about the inside of Earth and it’s layers.

How would you describe the motion of this wave? A. Body Waves Travel through the Earth’s interior. 1. P-waves (Primary/Compression Waves) push-pull waves that compress and expand the ground in the direction that the waves travel. How would you describe the motion of this wave?

2. S-Waves (Secondary/Transverse Waves) move the ground at right angles (up and down)to the direction that they travel. How would you describe the motion of this wave?

P- Wave S-Wave P & S Wave Animation What can this wave travel through? Travels through solids and liquids Travel Faster Arrives First Travels through solids, Cannot go through Liquids Travel Slower Arrives Second How would you describe the speed of this wave? When does this wave arrive compared to the other?

- Most destructive since they are on the surface B. Surface Waves –seismic waves that travel along the Earth’s outer layers (crust). - Follow P and S waves - Most destructive since they are on the surface China

C. Aftershocks and Foreshocks movements of the crust that follow a major earthquake called aftershocks. small vibrations called foreshocks come before a major earthquake. Anchorage, Alaska

III. Earthquake Zones The “Ring of Fire” is the area that surrounds the Pacific Plate which is marked with volcanoes and earthquakes.

Closure: Why would someone think that most earthquakes cause little damage and little loss of life? Because most occur in areas that are not populated by people or cities. Review Book: p.81-82 #1-10 2. 3. 4. 5. 6. 7. 8. 9. 10. Tokyo, Japan 3 4 3 4 1 1 1 1 2 Do the questions we did not do.

Aim: How do we locate Epicenters? Based on the diagram, how many seismograph station locations are necessary to find the epicenter of an earthquake?

I. Locating an Earthquake Epicenter The difference in arrival times of P and S waves help locate the epicenter. The greater the difference, the greater the distance to the earthquakes epicenter. Take a worksheet from the top bin to practice subtracting P and S wave times.

II. Distance to Epicenter (with one wave) Using the ESRT page 11 we can translate the time into a distance. … we can also use the same ESRT page to translate a distance into a time. Examples: A P-wave takes how long to travel 2600 km? An S-wave travels how far in 4 min? After 8 min and 20 sec. a P-wave travels? An S-wave travels 4.0 x 103 km in… 5 min 1000 km 5000 km 14 min

Work on questions 1 - 8 ONLY! Get an Earthquake P and S wave Travel Time worksheet from the top back bin. Work on questions 1 - 8 ONLY!

III. Distance to Epicenter (with two waves) Where does the difference between the P and S wave exist on this chart? “Spread Technique” Ex: S-wave – P-wave = 00:04:45 1) Use the time axis to mark off the difference in time. 2) Match the P and S wave lines with the marks you made. 3) Read down from this intersection to find the equivalent distance.

Complete the worksheet

IV. P- Wave Travel Time (or s-wave travel time) Use the distance from the previous step to find the travel time.

V. Origin Time The origin is when the earthquake began. (start) Subtract the arrival time from the travel time Origin (start) Travel Time Arrival (end)

V. Epicenter Location Data from three or more seismographs must be used to find the exact location of an earthquake epicenter. Epicenter - Use the distance to epicenter value and a protractor to draw these circles.

Closure: Looking at the chart on page11 of your ESRT, explain why the difference in travel time between the P and S wave increases as you move further from the epicenter of an earthquake. - Since the p-wave is faster, it travels farther than the s-wave in the same period of time. This causes the difference in travel time between the two to increase as distance from the epicenter increases. Review Book: p.89-91 #1-10 2. 3. 4. 5. 6. 7. 8. 9. 10. 4 2 3 1 2 3 2 3 2 3