Earthquakes Flashcards
What are Earthquakes?
An earthquake is the vibration of Earth produced by the rapid release of energy.
What is the focus of an earthquake?
The focus is the point in the earth’s crust where seismic energy is released.
What is the Epicenter of an Earthquake?
The Epicenter is the area on the surface directly above where the focus is.
Will an Earthquake be felt only in the Epicenter?
No, the waves generated will travel throughout the Earth
How to Earthquakes occur?
Through Elastic Rebound
Who discovered Elastic Rebound?
It was discovered by H.F. Reid in the 1900s.
What is Elastic Rebound?
Elastic Rebound is when two plates are moving along each other and get ‘stuck’. Pressure builds as they continue to try to move. The land deforms under the stress, and eventually, the pieces snap forward, releasing seismic energy.
Do Earthquakes occur all at once?
No, Earthquakes will often be accompanied by Aftershocks and Foreshocks.
What are Foreshocks?
Small Earthquakes that occur before a major earthquake. This can happen days or even years beforehand.
What are Aftershocks?
Adjustments that follow a major earthquake often generate smaller ones that occur afterwards.
What is Seismology?
The study of earthquake waves.
How old is Seismology?
Seismology dates bake 2000 years to the Chinese.
What are Seismographs?
Instruments that record Seismic waves.
How migh a seismograph have worked 2000 years ago in China?
They looked like golden eggs with dragons all around them. When seismic activity occurred, the dragon facing the direction the earthquake was in will drop the ball in it’s mouth into a cup.
How do Seismographs work today?
Modern Seismographs can pinpoint the x, y, and z co ordinates of an earthquake. The recording drum is anchored into bedrock, and as it shakes with the earth, a suspended mass bearing a pen that hangs from it remains still due to innertia. The drum moves around it and it records how the drum moves. A separate seismograph is required for horizontal and vertical ground movement.
What can we learn from Seismographs?
Behavior of Seismic waves.
Name the types of waves an Earthquake comes in.
The body waves, Primary (P) and Secondary (S) waves; and the Surface wave, Long (L) wave.
Describe P waves
P waves are the only waves that can travel through solids, liquids, and gases. As a result, they arrive fastest. They move in a compressive push-pull motion, and have the highest velocity of any of the waves.
Describe S waves
S waves can only travel through solids, and move in a shearing (S shaped) motion. Their amplitude and velocity are in the middle compared to the other waves.
Describe L waves
L waves travel exclusively along the surface of the earth. Their movements are complex, and the most destructive. They have the greatest amplitude of any of the waves, and have the longest periods of time between wave crests. They occur due to the combination of P and S waves. They are the slowest wave to arrive.
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