1. Unit 2: Earthquakes

2. What is an Earthquake?
The shaking of the Earth’s crust when two pieces of lithosphere move
Focus—original point of lithosphere motion deep inside of the Earth
Epicenter—place on Earth’s surface directly above the focus; used to report locations on a map

3. What Causes an Earthquake?
Caused by a sudden release of energy along a fault
Friction usually keeps the pieces of lithosphere from moving.
Too much stress is applied = friction is overcome = the pieces of lithosphere move.

4. Energy Release during Earthquakes
Seismic Waves—the energy released in every direction as lithospheric plates move
Come in 3 forms:
P waves
S waves
Surface waves

5. 1. P Waves = Primary Energy Waves
Travel the fastest of all seismic waves
Move THROUGH all of Earth’s layers
Compress and expand the Earth’s particles (energy moves parallel to the particles)

6. 2. S Waves = Secondary Energy Waves
Travel slower than P waves
Move THROUGH only the crust and mantle
Shift the Earth’s particles up and down (energy moves perpendicular to the particles)

7. 3. Surface Waves Travel the slowest of all of seismic waves
Move only along the Earth’s surface
Cause the most destruction of all wave types

8. Detecting Earthquakes: Seismometers
Seismometer—specialized instrument used to detect earthquakes
Records the timing and sizes of the 3 types of seismic waves as they pass through an area
Use data from or more seismometers to locate an epicenter via triangulation

9. Detecting Earthquakes: Epicenters
From the 3 seismometer station records, seismologists triangulate the epicenter from the DIFFERENCE in the arrival times of the waves at each station
The further away the earthquake = the bigger the difference in wave arrival times.

10. Detecting Earthquakes: Magnitude
Magnitude—the strength of the earthquake
Measured by the spike on the seismogram recorded as energy waves pass through an area
Ranked on the Richter Scale (1-10)
Each Richter measurement is about 10 times greater than the one below it

11. Likely Earthquake Locations
While earthquakes can occur at all boundaries, 75% of all of earthquakes are at convergent boundaries
The strongest earthquakes also happen at convergent boundaries