 What is it about earthquakes that make them so devastating?  Tell me what you already know about earthquakes.

 Each year, more than 30,000 earthquakes occur worldwide that are strong enough to be felt.  Only about 75 major earthquakes take place each year and often occur in remote regions  Essential Question: How do we locate an earthquake’s epicenter?

Unit 7

 Vibration of Earth produced by a sudden release of energy  Associated with movements along faults

 Earthquakes can be explained by this theory  The mechanism for an earthquake was first explained in the early 1900’s by H. Reid

 Rocks “spring back” in a process called elastic rebound  Vibrations occur as rock elastically returns to its original shape  The earthquake itself is often preceded by foreshocks and followed by aftershocks

 What do you think this is the study of? Earthquake waves  The instrument used to record the movements of the earth is called a seismograph  The record that is produced is called a seismogram

 1. Surface Waves: L waves Complex motion Slowest velocity  2. Body waves Two types:  Primary & Secondary

 Push-pull motion: compressional wave  Travel through solids, liquids, and gases  Greatest velocity of all earthquakes

 Shake motion  Travels only through solids  Slower than P waves

 Focus: the place within the Earth where the earthquake waves originate  Epicenter: the point on the surface, directly above the focus

 Located using the difference in the arrival times b/w P and S wave recordings, which are related to distance  Do you know what it means to triangulate a cell phone call?  It’s the same idea  In order to locate an earthquake 3 station recordings are needed

 A circle equal to the epicenter distance is drawn around each station.  The point where the circles intersect is the epicenter.

1. How long would it take P waves moving at 6.1 km/s to travel 100 km? How long would it take P waves to travel 200 km? 2. S waves move at 4.1 km/s. 100 km? 200 km? 3. What is the time lag between the arrival of P waves and S waves over a distance of 100 km? 200?

1. P waves: 100 km = 16.4 s 200 km = 32.8 s 2. S waves: 100 km = 24.4 s 200 km = 48.8 s 3. Lag time 100 km = 8 s 200 km = 16 s

 Mercalli intensity scale Assesses damage at a specific location Depends on: 1.Strength of earthquake 2.Distance from epicenter 3.Nature of surface material 4.Building design

 Concept introduced by Charles Richter in 1935  Measured on the Richter Scale  Depends on the amplitude of the largest wave recorded  Each unit of magnitude increase corresponds to a 10-fold increase in amplitude and a 30-fold increase in energy

 Largest earthquakes are near a magnitude of 8.6  Magnitudes below 2.0 are usually not felt

 Factors that determine destruction: Magnitude of earthquake Proximity to population  Destruction is caused by: Ground shaking Liquefaction of the ground Tsunamis Landslides Fires

 There is no reliable method for short- range prediction  Long-range: we can predict approximate locations based upon previous tectonic activity

 Research major earthquake activity along the San Andreas Fault over the past five years. Write a report on your findings.  Or  Research a major a earthquake in Earth’s history and write a report on your findings.

1. What are some differences between Primary (P) and Secondary (S) waves? 2. How do scientists pinpoint the location of an epicenter? 3. Name 3 types of destruction either caused or associated with earthquakes. 4. What is the focus of an earthquake?

 What does an engineer or architect need to think about when design a home in a location prone to earthquakes?  What are some ideas you have heard of or researched that have been implemented and successful?

 Simply use the materials available to you and construct a house.  Groups of 4 or 5 Teamwork is expected  You will have about 25 – 30 minutes to build your house.  Must be on cardboard.

 The deepest well drilled is only 12 km into Earth’s crust. With limited access, how do we know what Earth’s interior is like?

 Most of what we know about the interior of the Earth comes from the study of P and S waves

 Thin outer layer  Varies in thickness: 5km – 70km  Two types: Continental Crust: lighter granitic rock Oceanic Crust: basaltic composition

 Made up of the crust and uppermost mantle  ~100km thick  Cool, rigid, solid

 Thin layer that separates the crust from the mantle

 2885 km thick  Composed mostly of igneous rock  Asthenosphere  Upper mantle  Lower mantle

 Weak layer below the lithosphere in the upper portion of the mantle  Temperatures and pressures reach near melting point conditions for rocks

 More rigid than asthenosphere  Very hot  Rocks still have the ability to flow

 Below mantle  2270 km thick  Mobile liquid  Does not transmit S waves  Mainly iron and nickel  Related to Earth’s magnetic field

 1216 km radius  Solid  Iron and nickel composition  High density

 Describe how the three different types of seismic waves move and affect the movement of the material they pass over or through  You will most likely see this on your test…

 On a white sheet of paper, you will draw or construct a cross-section of Earth exposing the different layers.  You will need to label the layers and include: How thick Composition 1 other fact Needs to be colored