WRITE EVERYTHING IN YELLOW!

The Focus and Epicenter of an Earthquake

• The point within Earth where rock under stress breaks and triggers and earthquake is called the focus

• The point directly above the focus on the surface is the epicenter

A vibration that travels through Earth carrying energy released during an EQ.

Three types of seismic waves:Body waves

P wave S wave

Surface waves

Body waves P or primary waves

fastest waves travel through solids,

liquids, or gases compression wave,

material movement is in the same direction as wave movement

S or secondary waves slower than P waves travel through solids

only transverse waves -

move material perpendicular to wave movement

Surface Waves Travel just below or along the ground’s surface Slower than body waves; rolling and side-to-side

movement Especially damaging to buildings

What is the difference between surface waves and body waves?

What is the difference between surface waves and body waves? Surface waves move along the surface and

cause the most damage. Body waves run underground and cause little damage.

What is the difference between surface waves and body waves? Surface waves move along the surface and

cause the most damage. Body waves run underground and cause little damage.

What’s the differences between P waves and S waves?

What is the difference between surface waves and body waves? Surface waves move along the surface and

cause the most damage. Body waves run underground and cause little damage.

What’s the differences between P waves and S waves?P-waves are the fastest moving waves and are

a compressional wave. S-waves are slower and a tranverse wave. S-waves only travel through solids.

Seismographs record earthquake events

Seismic wave behavior P waves arrive first, then S waves, then surface waves Average speeds for all these waves is known After an earthquake, the difference in arrival times at a

seismograph station can be used to calculate the distance from the seismograph to the epicenter.

Damage in Oakland, CA, 1989• Building collapse

• Fire• Tsunami• Ground failure

most often caused by an underwater earthquakeearthquake must register at least 6.5 magnitudeonce the wave hits land, the wave slows and the

trough grows tall.

http://upload.wikimedia.org/wikipedia/commons/4/47/2004_Indonesia_Tsunami_Complete.gif

80% of all earthquakes occur in the Ring of Fire most of these result from convergent boundary activity ~15% occur in the Mediterranean-Asia belt remaining 5% occur in the interiors of plates and on

spreading ridge centers more than 150,000 quakes strong enough to be felt are

recorded each year

Mercalli Scale: rates Eqs from I-XII (roman numerals).Based on how the

earthquake affected people and buildings

Richter/Moment Magnitude: rates from 1-10.Reported by

seismograph machines around the world.

4.5 and below cause little damage