1. Journal #72
Draw a picture of an earthquake (lithosphere) label the focus, epicenter and fault.

2. Let’s Review: Earthquakes result from:
The sudden return of elastically deformed rock to is undeformed shape
The immobilization of faults
Zones where body waves cannot be detected
Movement between the layers that make-up Earth.

3. Let’s Review: What are the 2 types of Seismic Waves?
What are the 2 types of Body waves?
Which type of wave can me detected first?
What are the 2 types of surface waves?

4. Let’s Review:
Locations on Earth’s surface where no body waves from a particular earthquake can be detected are called _______zones.
Regions of a large number of closely spaced faults are called _______ zones.
Why do earthquakes generally take place at plate boundaries?

5. Today, we will summarize describe methods used by scientists to measure and record earthquakes.

6. Studying Earthquakes
The study of earthquakes and seismic waves is called seismology
Earthquakes are the best tool scientists have for investigating the Earth’s interior.
Scientists have developed equipment of recording, locating and measuring earthquakes.

7. Recording Earthquakes
Seismograph- an instrument that records vibrations in the ground.
One part records vertical motions of the ground
One part records horizontal motion (WestEast)
One part records horizontal motion (NorthSouth)

8. Recording Earthquakes
Seismographs record motion
The electronic signals can be recorded on magnetics tape that can be loaded onto a computer
Seismogram- tracing of earthquake motion that is recorded by a seismograph.

9. Recording Earthquakes
P waves are the first to be measured, followed by the slower S waves.
Surface waves, or Love and Rayleigh waves, are the slowest moving waves and are last to be recorded.

10. Recording Earthquakes
P waves are the first to be measured, followed by the slower S waves.
Surface waves, or Love and Rayleigh waves, are the slowest moving waves and are last to be recorded.

11. Locating an Earthquake
To determine the distance to an epicenter, scientists analyze the arrival times of the P waves and the S waves.
The longer the lag time between the arrival of the P waves and S waves, the farther away the earthquake occurred.
Scientists consult a lag-time graph- translates the difference in arrival times of the P and S waves into the distance from the epicenter.
The start time of the earthquake can also be determined by using this graph.

12. Earthquake Measurement
The amount of damage done by earthquakes and the energy released is measured by their magnitude and intensity.
Magnitude- is the measure of the strength and ground motion of an earthquake.
Magnitude is measured by a Richter scaled.
The larger the number, the stronger the earthquake

13. Earthquake Measurement
Intensity- the amount of damage caused by an earthquake.
This is measured by the Mercalli Scale which is expressed in roman numerals (I to XII)
XII is described as total destruction.
The intensity is dependent on the magnitude, the distance between the epicenter and affected area, local geology, earthquake duration, and human infrastructure.

14. Let’s Review What instrument is used to record seismic waves?
What is the difference between a seismograph and a seismogram

15. Let’s Review
What is the scaled used to measure the magnitude of an earthquake?
What scale is used to measure the intensity of an earthquake?
What factors affect the intensity of an earthquake?

16. Locating an Earthquake
To locate the epicenter of the earthquake scientists use computers to perform the calculations.
Prior to computers, scientists drew circles around at least 3 seismograph stations that recorded vibrations from the earthquake.
The radius of each circle was equal to the distance from that station to the earthquakes epicenter.
The point at which all the circles intersected indicated the location of the epicenter of the earthquake.