Earthquakes Natural vibrations of Earth’s ground caused by:

- Movement along tectonic plates

-OR

-Volcanic eruptions

Forces Within Earth

Fracture caused when:

-the forces acting on the Earth’s Crust exceed the strength of the Crust and Rocks

The Deformation of material caused by:

-Stress

In the Forms of:

- Compression

- Tension

- Shear

• Earthquakes occur at the boundaries of tectonic plates.

• See a lot of EQ’s in places like Japan and California.

• FACT: 3 million earthquakes happen every year!

Faults• A fault is the fracture or system of fractures along

which movement occurs.

• The surface along which the movement takes places is called the fault plane.

Types of Faults

Types of Faults

• Reverse faults are fractures that form as

a result of horizontal compression.

• Normal faults are fractures caused by horizontal tension.

• Strike-slip faults are fractures caused by horizontal shear.

• When rocks break during an earthquake energy is released in the form of seismic waves.• These waves travel in all directions.

• Focus is the exact point within the earth where the rock first breaks.

• Epicenter is the point on the surface immediately above the focus.

Waves spread out as a wave travels.

3 types of waves associated with an EQ

p-wave

s-wave

surface wave

P-WAVE• primary wave

• longitudinal type wave

• fastest wave: 6 km/sec

Longitudinal

S-WAVE

• secondary wave

• transverse wave• ½ speed of a p-wave: 3 km/sec

• they do not travel through liquids

Transverse

Transverse Waves

• A wave that causes the particles of the medium to vibrate perpendicularly to the direction the wave travels.

SURFACE WAVE

• they travel along earths surface

• it’s the wave you “feel” during an earthquake

• up/down and back/forth motion

• slowest of all 3 waves

Surface Waves

• Occurs in a liquid

• Circular particle motion

Surface Waves

• Occur at the boundary of two different mediums such as water and air.

Surface Waves cont

• Surface waves have a rolling pattern of particle motion.

Raleigh Waves

• Occurs in solid rock

• Particles move in elliptical path