What are earthquakes?

By: Mr. D'Angelone2 Key Terms Earthquake Focus Epicenter Seismic wave Seismograph

By: Mr. D'Angelone3 Tremors and Shakes Earth’s crust is always moving. Movements of the crust that you may or may not feel are called tremors. Sudden, strong, shaking movements of Earth’s crust are called earthquakes. Earthquakes can cause a lot of damage.

By: Mr. D'Angelone4 Focus and Epicenter Earthquakes begin deep within the Earth’s crust. The point where an earthquake starts is called the focus. The place on the Earth’s surface that is directly above the focus is the epicenter. The epicenter is the place where the Earth’s surface shakes the hardest.

By: Mr. D'Angelone5

6 What causes earthquakes? Earthquakes are associated with faults. Normal Fault – rocks are s-t-r-e-t-c-h-e-d apart by tensional forces Reverse Fault – rocks are squeezed together by compressional forces Strike-Slip Fault – rocks slide past each other

By: Mr. D'Angelone7 Rocks eventually break at the weakest point. As the rocks breaks, they release energy in the form of waves, or vibrations. These vibrations are called seismic waves.

8 Seismic waves Seismic waves travel out in all directions from the focus like when you throw a pebble in a pond.

By: Mr. D'Angelone9 Measuring Earthquakes A seismograph is an instrument that detects and measures earthquakes. It records the movements in Earth’s crust on a sheet of paper called a seismogram. The higher the waves are, the stronger the earthquake.

By: Mr. D'Angelone10 Checking Concepts 1.An instrument that detects and measures earthquakes is a ________. 2.An ________ is a sudden, strong movement of Earth’s crust. 3.Earthquakes start at the ________. 4.________ travel in all directions from the focus.

By: Mr. D'Angelone11 Answers 1.Seismograph 2.Earthquake 3.Focus 4.Seismic waves

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