1.What is an earthquake? 2.What causes earthquakes? 3.How are earthquakes measured? 4.What areas are more susceptible to an earthquake? Why? 5.What does an earthquake feel like?

The earthquake that caused the most destruction in history occurred in the Shansi province of China on January 23,1556. An estimated 830,000 people were killed. The second most destructive earthquake also occurred in China--in July, and killed 255,000 people.

The definition of an earthquake is… vibrations that cause the breaking of rocks. These vibrations move in all directions through the earth. They begin at a point along a fault.

The earth’s crust is constantly experiencing pressure from forces within and around it. This pressure builds up over time, and eventually causes the crust to break. This becomes a fault.

An earthquake begins along a fault (a crack in the earth’s surface) at a point called the focus. Directly above the focus is a point on the earth’s surface called the epicenter.

Focus Epicenter

Seismologists have stations all over the world that continuously collect information about earthquakes. This kind of information can help scientists figure out where larger, more destructive earthquakes may strike by mapping out the location of smaller ‘quakes. They also get a greater understanding of the changes the earth’s crust makes as the earthquakes occur. How do they do this???

When the fault ruptures with a sudden movement energy is released that has built up over the years. This energy is released in the form of vibrations called 'seismic waves'… earthquakes!'seismic waves It is actually when these seismic waves reach the surface of the earth that most of the destruction occurs, which we associate with earthquakes.

Earthquakes can cause landslides, sudden eruptions as in the case of a hot lava flow from a volcano or giant waves called tsunamis. Sometimes new land mass are also formed. Such earthquakes are attributed with the creation of the greatest undersea mountain range and the longest land mountain range.

…And that was just a 7.2 on the Richter scale!

Earthquakes are measured using the Richter Scale. The strongest earthquake ever measured was a 9.5 on the Richter Scale. This is a measurement of the amount of energy released from the earthquake.

9.5Chile, May 22, Indian Ocean (Sumatra tsunami) Dec 26, Prince William Sound, Alaska, March 28, Andreanof Islands, Aleutian Islands, Pacific, March 9, Kamchatka, Russia, November 4, Off the Coast of Ecuador, January 31, Rat Islands, Aleutian Islands, Pacific, February 4, India-China Border, August 15, Kamchatka, Russia, February 3, Banda Sea, Indonesia, February 1, Kuril Islands, Pacific, October 13, 1963

Magnitude is a number that characterizes the relative size of earthquakes & is proportional to energy released

In the lower 48 states, there is a tie between the February 1812, New Madrid, Missouri earthquake and the January 1857, Fort Tejon, California earthquake--both magnitude 7.9--for the strongest earthquake recorded.

Mercalli Scale

Generally, during an earthquake you first will feel a swaying or small jerking motion, then a slight pause, followed by a more intense rolling or jerking motion. The duration of the shaking you feel depends on the earthquake's magnitude, your distance from the epicenter, and the geology of the ground under your feet.

For minor earthquakes, ground shaking usually lasts only a few seconds. Strong shaking from a major earthquake usually lasts less than one minute. For example, shaking in the 1989 magnitude 7.1 Loma Prieta (San Francisco) earthquake lasted 15 seconds; For the 1906 magnitude 8.3 San Francisco earthquake it lasted about 40 seconds. Shaking for the 1964 magnitude 9.2 Alaska earthquake, however, lasted three minutes.

Aftershocks are smaller earthquakes which occur in the same general area during the days to years following a larger event or "mainshock". As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the main shock. The frequency of these aftershocks decreases with time.

Often, earthquakes can be a sign of things to come, like in the case of Mt. St. Helen’s in Washington.

This photograph was taken during the 1980 eruption. Is this volcano active again??? The seismic data says…YES!

Before After

Notice, this volcano really blew its top… literally! Mt. St. Helens Today