Finding the Epicenter

Finding the Epicenter

Multiple Choice

True or False: Seismograms are the machines that record, detect, and measure the vibrations of earthquakes.

• True

• False

Seismographs

• Seismographs are located all over the world

• If the earthquake is really strong, seismograph stations all over the world can record the same earthquake

Poll

Can an earthquake that occurs in Montana be recorded or felt in California?

• Yes

• No

• Maybe

• A seismograph in Montana can pick up an earthquake occurring in California.

• Why?

Earthquake Waves

Earthquakes waves that travel through the earth travel in all directions.

Focus

• The point where the earthquake occurs is called the FOCUS.

• It can be shallow or deep in the earth.

Epicenter

• The point on the earth’s surface directly above the focus is called the EPICENTER

• This is the place you usually hear about when there has been an earthquake.

Multiple Choice

What do we call the point where the earthquake ACTUALLY occurs?

• epicenter

• focus

Multiple Choice

What do we call the point on the earth’s surface ABOVE where an earthquake occurs?

• epicenter

• focus

Epicenter

• Seismologist use special math calculations to pinpoint the exact location of the earthquake’s epicenter

• 1. They use the arrival time of P and S waves as shown on several seismograms.

• 2. They plot those times on a special graph called a time- distance graph

Wave Travel Times

• P-waves always travel at the same average speed

• S-waves travel slower than P-waves

Wave Travel Times

• Both waves leave the point at the same time

• The distance between the two become greater and greater the farther they get from the starting line

• When each wave arrives at the station, seismologist subtract the difference to see how far away the earthquake’s epicenter is from their station. 

Find the time the P-Wave began

Multiple Choice

At what minute does the P-wave arrive?

• 1.5

• 2.25

• 5

• 6

Find the time the S-Wave began

Multiple Choice

At what minute does the S-wave arrive?

• 1.5

• 2.25

• 4

• 6

Subtract the S-wave time from the P-wave time. How many minutes apart are the S and P waves?

Multiple Choice

How many minutes apart are the S and P waves?

• 1

• 1.75

• 3

• 4.25

Locating the Earthquake

One seismograph station is not enough to pinpoint the exact location of an earthquake because the waves move outward in all directions

Poll

How many seismograph stations do scientists need to determine the location of an earthquake?

• 1

• 2

• 3

• 4

Multiple Choice

REVIEW: Which waves move faster: p-waves or s-waves?

• p-waves

• s-waves

Multiple Choice

REVIEW: Can seismographs determine the DIRECTION from which earthquake vibrations come from?

• Yes

• No

Multiple Choice

REVIEW: What is the recording or paper on which earthquake vibrations are recorded?

• Seismologist

• Siesmograph

• Seismogram

Multiple Select

REVIEW: What does a scientist use to determine the epicenter of an earthquake? Check all that apply (3).

• Data from three stations

• Time-Distance Graph

• Richter Scale

• Lag time between P and S waves

• Data from two stations