Transcript 19.1 Forces within the Earth

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