Earthquakes, Section 2 Measuring Earthquakes

1
Earthquakes, Section 2 (Measuring Earthquakes)
2
Facts about Earthquakes

• Up to 8000 earthquakes per day
• Always begin in rock below surface
• Earthquakes start at a focus point.
• Focus Point is beneath the earth where the
  earthquake begins
• Epicenter is the point on the surface directly
  above the focus point.

3

• Seismic Waves
• Are vibrations that travel through the earth
  carrying the energy released during an earthquake

4
3 Categories of Seismic Waves

• Primary waves
• Secondary waves
• Surface waves.

5
P waves

• Earthquake waves that compress and expand the
  ground like an accordion.
• Can only move through solids and liquids.

6
S waves

• Earthquake waves that vibrate from side to side
  as well as up and down. Shake the ground back
  and forth.
• Comes after a P wave.
• Can move through only solids.

7
Surface waves

• P waves and S waves can turn into surface waves.
  
• Move more slowly than P and S waves, but are the
  most violent.
• Shakes building side to side and can cause
  rolling type of movements.

8
Detecting Seismic Waves

• Seismograph
• Records ground movements.

9
Measuring Earthquakes

• Magnitude measurement of earthquake strength
  based on seismic waves and movement along faults.
• Richter Scale rating of the size of seismic
  waves. Only good for small nearby waves.
• Moment Magnitude Scale used to rate earthquakes
  of all sizes, near or far.

10

• Locating the Epicenter
• Need at least 3 sets of data from 3 different
  areas to locate an epicenter