Earthquakes

Earthquake waves are called…

• The types are P, S, and L waves

Seismic Waves

P - waves

• Travel the fastest

• They arrive first and thus are called primary waves

• Travel through solids, liquids and gases

• Are longitudinal waves with compressions and rarefactions

S - Waves

• Travel Slower

• Arrive later and are thus called Secondary waves

• Travel through solids but not liquids or gases

• Are transverse (or shear) waves with crests and troughs

P-waves & S-waves

L - Waves

• Are the slowest moving

• Arrive after the P and S waves

• Originate on the earths surface thus are called surface waves

• Move in a circular motion like water waves

• Cause the most damage during an earthquake because the bend and twist the Earth’s surface

Focus and Epicenter

• The point underground where the earth quake originates is called the focus.

• The place on the Earth’s surface directly above the focus is called the epicenter.

A seismograph consists of a weight attached to a spring or wire. A pen attached to the weight records anymovement of the Earth on a sheet of paper wound around a constantly rotating drum.

Seismograph

• Instrument that detects and measures seismic waves

Richter Scale

• A scale used to compare the strength of earthquakes

• Each number on the Richter scale represents an earthquake 10 times stronger than the number below it.

• Any number above 6 represents a very destructive earthquake.

P and S waves originate at the epicenter (left).

P-waves travel fastest and through all types of matter (solid, liquid and gas.)

S-waves travel slower and only through solids.

Is the crust all one piece?• No, the crust is divided into many “plates”.

The boundaries between plates are called “faults”.

Why does the Earth quake?

• The entire crust of the Earth is floating on a liquid layer of mantle (even the oceans).

At the faults the plates can……slide past each other, pull away from each

other or push against each other.

The plates pushing together……can cause mountains to push up and

earthquakes.

Plates pulling apart can cause…

…deep trenches and volcanoes.

Plates sliding past each other……build up tension. When this tension is

released, earthquakes occur.

San Andreas Fault

Continental Drift …

Is the theory that the continents are all drifting continuously and that millions of years ago the were in very different locations.

Focus of Haiti Earthquake

The recent quake in Haiti (Hispaniola) occurred along a fault.

Damage to buildings

Damage to buildings

Alaska

When you think of Alaska, you may not think of Earthquakes…

…but Alaska has more earthquakes than any other state.

In fact, Alaska has a magnitude 7 quake almost every year.

Not much is heard about this because human casualties are usually not too high as not a lot of people live in the earthquake zones.

Alaska had a 9.2 magnitude earthquake in 1964.

This is the most violent earthquake ever recorded in the United States, but only about 100 people died.

California is much better known for earthquakes.

• They do have a lot of quakes, but the main reason is the large population that is affected.

The San Francisco quake

of…

… 1906 killed an estimated 3000 people.

The fire that followed destroyed 28,000 buildings and made 225,000 people

homeless.

The city hall was one of the casualties.

The San Francisco quake of 1989…

…killed 62 and left 12,000 people homeless.

The Bay Bridge collapsed upon itself.