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The Changing Earth. Chapter Eleven: Earthquakes and Volcanoes. 11.1 Earthquakes. What is an. An earthquake is the shaking and trembling that results from the sudden movement of part of the earth’s crust. 11.1 What is an earthquake like?.
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Chapter Eleven: Earthquakes and Volcanoes • 11.1 Earthquakes
What is an • An earthquake is the shaking and trembling that results from the sudden movement of part of the earth’s crust.
11.1 What is an earthquake like? • When you throw a pebble into a pond, waves move outward in all directions. • In a similar manner, when rocks in the Earth’s crust break, earthquake waves travel through the Earth in all directions.
11.1 What are earthquake? Earthquakes are a natural disaster.
11.1 What causes earthquake? The most common cause of earthquakes is faulting; a break in the Earth’s crust.
11.1 What causes earthquake? • During faulting, parts of the Earth’s crust are pushed together or pulled apart. • As the rock slides, energy is released in the form of waves causing shaking and trembling.
How many earthquakes per year? • Estimated that 1 million earthquakes occur each year. • About 3 per year cause severe changes in the Earth’s surface.
San Andreas Fault Land on the west side of the fault moves north and land on the east side of the fault moves south
Do earthquakes occur in the ocean? • Yes they do!!! • Earthquakes occur on the floor of the ocean. • As a result, Tsunami waves occur which are extremely destruction. • Entire countries can be destroyed.
Tsunami in Japan March 11th, 2011 • It was a 9.0 magnitude undersea mega-thrust earthquake off the coast of Japan • It was extremely destructive tsunami waves up to 23.6 meters or 77 feet high. • The Japanese National Police Agency confirmed: • There were10,872 deaths and 2,776 injured, • 16,244 people were reported missing, • Also,125,000 buildings were destroyed or damaged, and extensive damage to roads and railways.
11.1 What causes earthquakes • The point below the surface where the rock breaks is called the earthquake focus.
11.1 What causes earthquakes • The focusis the underground point of origin of an earthquake.
11.1 What causes earthquakes? • As soon as the rock breaks, there is movement along the broken surface causing a split in the surface called a fault.
11.1 What causes earthquakes? • The seismic waves from an earthquake are usually strongest at the epicenter, the point on the surface right above the focus.
11.1 What causes earthquakes? • The epicenter is directly above the focus on the Earth’s surface. Earthquake waves reach the epicenter first and are the most violent.
11.1 Seismic waves • A seismologist is a scientist who studies earthquakes. • Seismic waves are recorded and measured by an instrument called a seismograph. • Seismic waves inside Earth are called body waves. • The two main types of body waves are P-waves and S-waves.
11.1 Seismic waves • After an earthquake occurs, the first seismic waves recorded will be P-waves. • S-waves are recorded next, followed by the surface waves.
