Earthquakes Release Energy
- The vibrations caused by earthquakes
Focus and Epicenter
- Focus - the of an earthquake is the pint underground where the rocks first begin to move.
- Epicenter - the point of the Earth’s surface directly above the focus.
- Scientists often name an earthquake after the city that is closest to the epicenter
Waves and Energy
- Earthquakes produce three types of waves
- These are the fastest seismic waves
- Average speed 5km/sec (3mi/sec)
- Can pass through solids, liquids and gases
- Travel at about ½ the speed of P-waves
- Start at the same time as P-waves
- Can travel through solids (rocks) NOT through liquids or gases
- Seismic waves that move along Earth’s surface, not through it’s interior
- Make the ground roll or shake from side to side
- Cause the largest ground movements and the most damage.
- The slowest type of seismic waves
Read page 116 (B), using seismographs
- An instrument that constantly records ground movements
- Scientist must have at least 3 seismic stations
- Scientist find the difference between the arrival times of the P and S waves at each of the three stations
- The time difference is used to determine the distance of the epicenter from each station. The greater the difference in time, the farther away the epicenter is.
- A circle is drawn around each station, with a radius corresponding to the epicenters distance from that station. The point where the 3 circles meet is the epicenter