8.1 What is an Earthquake?
How long is the San Andreas fault?
1300 kilometers
How many earthquakes occur worldwide?
30,000
How much did the land on the western side of the San Andreas fault move during the 1906 earthquake in San Francisco?
4.7 meters to the north
How long did the intense shaking of the 1906 San Francisco earthquake last?
40 seconds
How many major earthquakes take place each year?
75
Fault
A break in the earth's crust
Aftershock
An earthquake that occurs after a larger earthquake in the same area
Where do these Earthquakes occur?
Most of these occur in remote regions. However, occasionally a large earthquake occurs near a city.
Epicenter
Point on Earth's surface directly above an earthquake's focus
What is the most studied fault system in the world?
San Andreas fault
The San Francisco earthquake caused what?
They caused horizontal shifts in Earths surface of several meters along the northern portion of the San Andreas fault
What is the point within the Earth where the earthquake is called?
a focus
Foreshock
a small burst of shaking that occurs before a large earthquake
List three pieces of evidence that are used to show that the earth is shaking.
a) the crust has been uplifted at times b) there have been evidence of many ancient wave-cut features meters above the level of the highest tides c)offsets in fence lines, roads and other structures indicate that horizontal movements of earthquakes
How are earthquakes caused?
by a slippage along a break in Earths crust
How are earthquakes produced?
by the rapid release of elastic energy stored in rock has been subjected to great force. when the strength of the rock is exceeded, it suddenly breaks,causing the vibrations of an earthquake
Describe the cause of earthquakes.
earthquakes are often caused by slippage along a break in Earth
What is the source of an earthquake called?
focus
In what directions do released energy go?
the directions can go in all directions from the focus in the form of waves which are similar to the waves produced when a stone is dropped in a calm pond
Elastic Rebound Hypothesis
the explanation stating that when rocks are deformed, they break, releasing the stored energy that results in the vibrations of an earthquake
Focus
the point within earth where the earthquake starts
what is a realistic rebound?
the springing back of the rock into its original place
Earthquake
the vibration of Earth produced by the rapid release of energy
How early can these minor quakes occur before the major one?
these minor quakes can occur days or even years before a major quake
