Download Seismic Wave

SEISMIC WAVE NOTES
Seismic Waves - Waves of vibration that occur during an earthquake. They spread out in
all directions from the earthquake focus.
1. Focus - Point inside the Earth where the earthquake originates.
2. Epicenter - Point on the surface directly above the focus.
There are 2 main types of waves. There are two different types of each main type.
1. Body Waves - Occur on the inside of the Earth.
A. P-waves - Primary waves and they are the fastest.
B. S-waves - Secondary waves. Rock particles move at right angles to the
direction of wave motion. Does not go through liquids.
2. Surface Waves - Occur on the Earth's surface.
A. L-waves - Longitudinal waves that travel upwards from the focus to the
epicenter, then along the Earth's surface. They are the most destructive of
all seismic waves.
B. R-waves - Least destructive of all seismic waves.
WAVE
WAVE TYPE
PASSES THRU
SPEED (km/s)
WAVE MOTION
P
BODY
L and S
4.9 - 7.5
PUSH/PULL
S
BODY
SOLID ONLY
2.8 - 6.3
SHEARING
R
SURFACE
L and S
5.4 - 7.4
CIRCULAR
L
SURFACE
L and S
4.9 - 5.4
PUSH/PULL
Seismograph - Used to detect and measure seismic waves.
1. Primary - First waves that are recorded on seismograph.
2. Secondary - Follows the primary wave. Slower wave than primary.
3. Longitudinal - Last wave to be recorded. It is the slowest wave.
The further away the seismograph is from the epicenter, the longer the interval between
the appearance of the primary and the secondary waves. One measurement taken with
the seismograph is:
Amplitude - The vertical distance above or below the Zero (0) line. The stronger the
earthquake, the greater the distance above or below the 0 line.
Richter Scale - Earthquakes are measured on this scale. Other scales are used as well.
- Divided into ten units (0-10)
- Each number represents an earthquake 10X stronger than the earthquake
represented by the number preceding it. Rises by a factor of 10 each time.
Magnitude – The amount of energy is released by the earthquake.
Predicting Earthquakes
1.
2.
3.
4.
5.
Tilt meter - Reveals changes in the tilt of the Earth's surface.
Creep meter - Measures the horizontal movement of the Earth's surface.
Gases - Released by the Earth into well eater or springs before an earthquake.
Well water - The level of the water changes before an earthquake.
Animals - They become unusually nervous and excited before an earthquake.
Fault Types
Fault - Crack in the Earth's crust along which some movement occurs.
1. Normal - Forms when the rocks above the fault surface move down. Tension
2. Reverse - Forms when the rocks above the fault surface are pushed up over the rocks
on the other side. Compression
3. Strike-slip - Forms when the rocks on either side of the fault slide past each other.
Shearing