EARTHQUAKES 2007 Japan quake

EARTHQUAKES What are earthquakes? They are a shaking of the ground. 1906 San Francisco quake,evacuation by sea

The Study of Earthquakes What is seismology? It is the study of earthquakes Where do most earthquakes occur? Near the edges of tectonic plates. What are tectonic plates? Giant pieces of Earth’s thin, outermost layer Tectonic plates move in different directions and at different speeds Two plates can push toward or pull away from each other. They can slip slowly past each other. What happens as a result of these movements of plates? A fault A fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another. Earthquakes occur along faults because of this sliding

What Causes Earthquakes? As tectonic plates push, pull or slip past each other, stress increases along faults near the plate’s edges. This causes the rock to deform What is deformation? It is the change in the shape of rock in response to stress. How many ways does a rock deform? Two In a plastic manner or in an elastic manner Plastic deformation does not lead to earthquakes What type of deformation does lead to earthquakes? Elastic deformation What is elastic rebound? The sudden return of elastically deformed rock to its original shape What is released during elastic rebound? Energy What does some of this energy travel as? Seismic Waves, which causes earthquakes

Plate Motion and Fault Types Plate Motion Fault type Transform strike-slip fault convergent reverse fault Divergent normal fault

Faults at Tectonic Plate Boundaries What is transform motion? It occurs where two plates slip past each other Transform motion creates strike-slip faults. Blocks of crust slide horizontally past each other What is convergent motion? It is where two plates push together Convergent motion creates reverse faults. Blocks of crust that are pushed together slide along reverse faults What is divergent motion? It occurs where two plates pull away from each other Divergent motion creates normal faults. Blocks of crust that are pulled away from each other slide along normal faults

How Do Earthquake Waves Travel? What are waves of energy that travel through the Earth called? Seismic Waves Seismic waves that travel through the Earth’s interior are called what? Body waves What are the two types of body waves? P waves and S waves What are seismic waves that travel along earth’s surface called? Surface waves Waves that travel through solids liquids and gases are called P waves. P waves are the fastest waves, so they travel ahead of other seismic waves. What are P waves also called? Primary waves because they are the first to be detected in an earthquake When are S waves created? When rock deformed from side to side springs back to its original position What is another name for S waves? Shear waves They are the second fastest of the seismic waves They stretch the rock sideways They arrive after P waves and are also called secondary waves Surface waves move along the earth’s surface and produce motion mostly in the upper few kilometers of Earth’s crust

Earthquake Measurement How do scientists know when and where earthquakes begin? They depend on seismographs What is a seismograph? An instrument located at or near the surface of the Earth that record seismic waves When the waves reach a seismograph it creates a seismogram What is a seismogram? The tracing of earthquake motion Seismologists use seismograms to calculate when an earthquake began How do seismologists find the start time of an earthquake? They find it by comparing seismograms and noting the differences in arrival times of P waves and S waves. What is an epicenter? It is the point on Earth’s surface directly above an earthquakes starting point What is a focus? The point inside the Earth where an earthquake begins

Seismograph Seismogram being created

Measuring Earthquake Strength and Intensity The Richter Scale was used to measure strength of earthquakes throughout the 20th century Who designed the Richter Scale? Charles Richter in the 1930s What is the measure of the strength of an earthquake called? Magnitude What is intensity? The measure of the degree of an earthquake felt by people and the amount of damage caused What is used to measure intensity of an earthquake? The Modified Mercalli Intensity Scale

Earthquakes and Society Why is it important for people in earthquake zones to be prepared before an earthquake strikes? Seismologists are not always able to predict the exact time and place when an earthquake will occur. What is an earthquake hazard? It is a measurement of how likely an area is to have damaging earthquakes in the future. What is retrofitting? It is the process of making older structures more earthquake resistant.