Starter 11/18/14 What evidence is there for plate tectonics? The Earth is currently in ______ polarity. Deep focus earthquakes are associated with ocean ______. Why do the tectonic plates move?

Starter

8.1 What is an Earthquake? P. 74 Today, you will be able to: http://geography-site.co.uk/pages/physical/earth/images/plates.gif Today, you will be able to: Compare/contrast the epicenter and focus of an earthquake. Identify the cause of earthquakes. Compare and contrast aftershocks and foreshocks.

Vocabulary (Index Cards) Earthquake Focus Epicenter Fault Aftershock Foreshock Seismograph Seismogram Surface wave S wave P wave

What type of plate boundary causes earthquakes? Transform fault

What Is an Earthquake?  An earthquake is the vibration of Earth produced by the rapid release of energy  Focus and Epicenter • Focus is the point in Earth (under the crust) where the earthquake starts. • Epicenter is the location on the surface directly above the focus.  Faults • Faults are fractures in Earth where movement has occurred. Fault creep- the slow, gradual, smooth fault movement

Focus, Epicenter, and Fault

Slippage Along a Fault

What Is an Earthquake?  Elastic Rebound Hypothesis • Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces. • When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake. Seismic wave- energy that radiates in all directions from the earthquakes origin (starting point = focus)

Elastic Rebound Hypothesis

What Is an Earthquake?  Aftershocks and Foreshocks • An aftershock is a small earthquake that occurs after the main earthquake. • A foreshock is a small earthquake that occurs before a major earthquake (can happen years before a major earthquake).

8.2 Measuring Earthquakes p. 74 http://geography-site.co.uk/pages/physical/earth/images/plates.gif Today, you will be able to: Identify the three types of seismic waves. Explain how to locate the epicenter of an earthquake. Identify other dangers associated with earthquakes. Explain the potential for earthquake prediction.

Measuring Earthquakes Seismographs are instruments that record earthquake waves. Seismo=shake  Seismograms are traces of amplified, electronically recorded ground motion made by seismographs. Surface waves are seismic waves that travel along Earth’s outer layer. Most destructive waves

Seismograph

Seismogram

Measuring Earthquakes  Body Waves • Identified as P waves or S waves • P waves - Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel - Travel through solids, liquids, and gases - Have the greatest velocity (speed) of all earthquake waves

Measuring Earthquakes  Body Waves • S waves Seismic waves that through Earth’s interior - Shake particles at right angles to the direction that they travel - Travel only through solids - Slower velocity than P waves  A seismogram shows all three types of seismic waves—surface waves, P waves, and S waves.

Seismic Waves

Measuring Earthquakes  Earthquake Distance • The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance.  Earthquake Direction • Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter.  Earthquake Zones • About 95 percent of the major earthquakes occur in a few narrow zones.

Locating an Earthquake

Measuring Earthquakes Historically, scientists have used two different types of measurements to describe the size of an earthquake  intensity and magnitude. Intensity = amount of shaking based on damage Magnitude =measure of the size of seismic waves  Richter Scale • Based on the amplitude of the largest seismic wave 5.0 is 10x greater than 4.0 • Does not estimate adequately the size of very large earthquakes

Measuring Earthquakes  Momentum Magnitude • Derived from the amount of displacement (movement) that occurs along the fault zone • Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes. • Measures very large earthquakes

Earthquake Magnitudes

Some Notable Earthquakes

NC Seismic Activity Earliest record earthquake activity March 8, 1735 Earthquakes in Missouri were felt throughout NC in 1811 East coast earthquakes felt over a larger area because east coast made of older rock that has not been fractured

Post-Test (page 64) In what order do the basic types of seismic waves reach a seismograph? Describe the differences in speed and mode of travel between primary (P) waves and secondary (S) waves. Write a paragraph describing in your own words an earthquake that has been measured as a moment magnitude of 6.0.

Seismic Risk Map (page 61) Use Textbook to identify states p. 744

Pangaea Puzzle (page 57) Red Blue Yellow Pink Orange Purple Green

Pangaea Puzzle (page 57)

Earth’s Layers Foldable (page 59)

Plate Boundaries (page 61)

Plate Boundaries (page 61)

Plate Boundaries (page 61)