1. Locating Earthquakes Chapter F5
Section 2 Earthquake Measurement
Locating Earthquakes
Scientists use seismographs to study earthquakes.
A seismograph is an instrument that records vibrations in the ground and determines the location and strength of an earthquake.
When earthquake waves reach a seismograph, it creates a seismogram, a tracing of the earthquake’s motion.

2. Locating Earthquakes, continued
Chapter F5
Section 2 Earthquake Measurement
Locating Earthquakes, continued
Determining Time and Location of Earthquakes Seismograms are used to find an earthquake’s epicenter.
An epicenter is the point on the Earth’s surface directly above an earthquake’s starting point.

3. Locating Earthquakes, continued
Chapter F5
Section 2 Earthquake Measurement
Locating Earthquakes, continued
A focus is the point inside the Earth where an earthquake begins.
An earthquake’s epicenter is on the Earth’s surface directly above the earthquake’s focus.

4. Locating Earthquakes, continued
Chapter F5
Section 2 Earthquake Measurement
Locating Earthquakes, continued
The S-P Time Method is perhaps the simplest method by which seismologists find an earthquake’s epicenter.
This method is explained in the following Visual Concepts presentation.

5. S and P Time Method: Finding an Epicenter
Chapter F5
Section 2 Earthquake Measurement
S and P Time Method: Finding an Epicenter
Click below to watch the Visual Concept.
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Visual Concept

6. Chapter F5 Measuring Earthquake Strength and Intensity
Section 2 Earthquake Measurement
Measuring Earthquake Strength and Intensity
The Richter Magnitude Scale Throughout much of the 20th century, seismologists used a scale created by Charles Richter to measure the strength of earthquakes.
Earthquake Ground Motion A measure of the strength of an earthquake is called magnitude. The Richter scale measures the ground motion from an earthquake and adjusts for distance to find its strength.

7. Richter Scale Chapter F5 Section 2 Earthquake Measurement
Click below to watch the Visual Concept.
You may stop the video at any time by pressing the Esc key.
Visual Concept

8. Chapter F5 Measuring Earthquake Strength, continued
Section 2 Earthquake Measurement
Measuring Earthquake Strength, continued
Modified Mercalli Intensity Scale A measure of the degree to which an earthquake is felt by people and the damage it caused is called intensity.
Currently, seismologists use the Modified Mercalli Intensity Scale to measure earthquake intensity. This is a numerical scale that uses Roman numerals from I to XII to describe earthquake intensity levels.

9. Chapter F5 Measuring Earthquake Strength, continued
Section 2 Earthquake Measurement
Measuring Earthquake Strength, continued
In the Modified Mercalli Intensity Scale, an intensity of I describes an earthquake that is not felt by most people. An intensity level of XII indicates total damage of an area.
Because the effects of an earthquake vary based on location, any earthquake will have more than one intensity value. Intensity values usually are higher near the epicenter.