1. Chapter 12 - Section 2 Measuring Earthquakes

2. WHAT WE KNOW…
Earthquakes are the shaking of Earth’s crust caused by release of energy as lithospheric plates shift
Focus: the point within Earth where seismic activity begins
Epicenter: the point on Earth’s surface directly above the focus.

3. LOCATING AN EPICENTER Use triangulation:
Data from 3 different seismograph stations
Look at time lapse (time difference) between the arrival of P waves and S waves
The longer the lag time between P & S waves the farther you are from the earthquake’s epicenter.

4. MAGNITUDE strength or amount of energy released
It is a measure of the amount of ground motion
Measured using the Richter scale

5. Measures the magnitude of an earthquake on a 10 point scale.
Richter Scale
Measures the magnitude of an earthquake on a 10 point scale.
Richter magnitude is determined by measuring the largest amplitude (wave height) recorded on the seismogram.

6. RICHTER SCALE
Each increase in 1 on the Richter Scale represents a 10 fold increase in the wave magnitude.

7. INTENSITY
A measure of the effect of an earthquake, uses the Mercalli Scale
Dependent on:
1. magnitude of earthquake
2. distance from epicenter
3. type of rock underlying region
4. construction of building
Varies for each event

8. MERCALLI SCALE Mercalli Scale Description of what happened
Roman numerals
XII total destruction
Not a true indication of the actual
strength of an earthquake

9. MERCALLI SCALE

10. Magnitude vs. Intensity
Would it be possible for an earthquake in two locations to have the same MAGNITUDE on the Richter Scale but a different INTENSITY on the Mercalli Scale?
Why or why not?

11. Richter and Mercalli Scales