EarthquakeWaves

Focus: point in Earth where energy is released

Epicenter: point on surface above earthquake

Richter Scale measures magnitude of an earthquake- a magnitude 7 has 10x more ground movement than magnitude 6

Types of Seismic Waves– Primary waves (p waves)

• Fastest waves• Can travel through any material

– Secondary waves (s waves)• Slower than P waves• Can travel only through solids (no liquids)

– Surface waves (l waves)• Energy waves that reach the Earth’s surface• Most damaging earthquake waves

Speed up when going through Denser material. These are the fastest waves!

These waves can only travel through solids. Slower than P-waves.

P waves S waves

Primary Waves Secondary Waves

Travel faster, and at seismic stations first. Travel slower, and arrive at seismic stations second.

Push-pull, or compression waves. Side-to-side, or shear waves.

Travel through solids, liquids, and gases. Travel only through solids.

Surface waves • L – Waves• Slowest waves • Most destructive!!!

Earthquake Damage & Loss of Life Depend On:

• Earthquake magnitude• Duration of ground movement

• Depth of focus

• Type of ground particles

• Building design

• Fire / Landslides / Tsunami

• Emergency and medical services Video on Haiti earthquake magnitude 7.0

Tsunami

Seismic risk in U.S.

Faults in North Carolina

Let’s Review…How do scientists know what the Earth’s interior is made of?

Moho Boundary• Discovered in 1909 by Andriji Mohorovicic.• Boundary between Crust & Mantle. • Change in speed of seismic waves!!!

Remember, Earth is composed of layers

Liquid Outer Core: Iron-Nickel Liquid• S waves stop at a depth of 2900 kilometers since

they cannot travel through liquids• P waves also slow down because less dense

– Composed of liquid iron and nickel.

Inner Core: Solid Iron-Nickel Metal– P waves speed up

Seismograph – Device used to Measure Earthquake Waves

Seismogram – the record of the ground shaking made by a seismograph

• Determines:–Speed of Waves–Distance to earthquake’s epicenter

Seismogram• Average time travel of P &

S waves. • Find time between P & S

wave. • Go vertically to find the

distance from the epicenter.

Example to Do Together:

To find the Epicenter you need at least 3 stations distances! (triangulation)

Locating the epicenter of an earthquake

• Use distances of earthquake from three observatories.

•Use a compass

• Intersection of circles determines epicenter

San Francisco

Denver

Tucson