1. Earthquake Measurement
Locating Earthquakes
seismographs: instruments located at or near the surface of the Earth that record seismic waves.
seismogram: a tracing of earthquake motion that is created by a seismograph.

2. Earthquake Measurement
- seismologists find an earthquake’s start time and location by comparing the arrival of P waves & S waves.
epicenter: the point on Earth’s surface directly above an earthquake’s starting point, or focus.
focus: the point along a fault at which the first motion of an earthquake occurs.

3. Earthquake Measurement
- the S-P time method is used to triangulate the location of an earthquake by comparing the distances both waves traveled from three seismic stations (Figure 3 – pg.137).
Japan
Seismic Station #3
Pakistan
Seismic Station #1
2004 Indonesia Tsunami
(230,000+ killed)
Australia
Seismic Station #2

4. Earthquake Measurement
Measuring Earthquake Strength & Intensity
- most seismologists use the Richter Scale to measure the magnitude of an earthquake.
- magnitude is calculated by the amount of ground motion.

5. Earthquake Measurement
- each increment is a factor of 10, so magnitude increases 10x per additional measurement.
- for example, the ground motion by a 7.0 earthquake will be 1,000 times greater (10x10x10) than a 4.0 earthquake.
- therefore, the difference between a 2.0 earthquake and a 9.0 earthquake can be calculated using the following formula: 10x10x10x10x10x10x10 = ___________________
10,000,000x

6. Earthquake Measurement
- the amount of damage an earthquake causes is referred to as intensity.
- the Mercalli Scale is used to measure intensity by applying Roman Numerals to destruction