How and Where Earthquakes Occur
1. Compare and contrast primary, secondary, and surface waves.
2. Explain how an earthquake epicenter is located using seismic wave information.
3. Describe how seismic wave studies indicate the structure of the Earth's interior.
seismic wave focus primary wave epicenter surface wave inner core outer core mantle crust
U.S. Geological Survey, Home page
than 3 million earthquakes occur every year. Earthquakes are caused by the
reshaping of Earth through the movement of Earth's tectonic plates. Most
earthquakes occur along plate boundaries or along cracks in the lithosphere
called faults. To understand the formation of faults it is important to
remember that all rocks have the
quality of elasticity (ability to return to shape).
When rock (lithosphere)
is stretched beyond its elastic limit it forms a fault.
Caused by plate movements
The stretching &
breaking of the rock builds up energy which when released causes an earthquake!
The energy of the earth is released in seismic
waves which travel outward from the focus.
Focus- point where the energy is
Epicenter – place on the surface of the
Earth above the focus
Primary (P) waves – type of seismic wave
that vibrates rock back and forth
Squeeze & stretch rock
Travels through - air, rock, water (everything)
Secondary (S) waves – cause particles to move up and down
Transverse (shear) waves
Travels through - solid (not through liquid or gas)
Surface waves – travel out from the epicenter
- Elliptical motion – Transverse + longitudinal
Love - side to side motion
Cause the most surface destruction