Login
Copyright

What is a Seismograph? - Definition, History & Facts

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: What is an Earthquake? - Definition & Explanation

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:00 What's a Seismograph?
  • 1:00 How a Seismograph Works
  • 2:00 Measurement Scales
  • 3:15 The First Seismograph
  • 3:55 Fun Facts
  • 4:50 Lesson Summary
Add to Add to Add to

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Login or Sign up

Timeline
Autoplay
Autoplay
Create an account to start this course today
Try it free for 5 days!
Create An Account

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Mary Ellen Ellis
Read about the seismograph, what it measures, how it works, and how it has helped scientists to better understand earthquakes both in the past and today.

What's a Seismograph?

Earthquakes are fascinating and frightening at the same time. Have you ever wondered how scientists study these earth-shaking events? They use what's called a seismograph, also called a seismometer, which is an instrument that measures and records seismic waves that move through the earth as the result of an earthquake.

A modern seismograph can help scientists detect earthquakes and measure several aspects of the event:

  • The time at which the earthquake occurred
  • The epicenter, which is the location on the surface of the earth below which the earthquake occurred
  • The depth below the earth's surface at which the earthquake occurred
  • The amount of energy released by the earthquake

Scientists measure and record this data to learn more about earthquakes, tectonic plates, and Earth's layers. Earthquakes are difficult to predict, but scientists studying them hope to use seismographic measurements to be able to make more accurate predictions.

How a Seismograph Works

The idea behind a seismograph is fairly simple. A basic seismograph includes a solid base and a heavy weight suspended from a spring over the base. A pen hangs from the weight and a rotating drum with paper sits below it on the base. The tip of the pen touches the drum. When the earth shakes from an earthquake, the drum rotates, and the weighted pen moves back and forth due to the motion of seismic waves. The pen records the movement on the drum. The paper recording of an earthquake is called a seismogram.

The most high-tech seismographs used by scientists studying earthquakes today are sophisticated and precise. They are based on the same concept as a basic, simple seismograph, but make use of electronics, magnets, and amplifiers in order to accurately and precisely measure the smallest ripples in the earth caused by earthquakes.

Measurement Scales

You have probably heard of the Richter scale, a popular unit for measuring the magnitude of an earthquake. It was invented by Charles F. Richter of the California Institute of Technology in 1935 and uses a logarithmic scale to measure seismic wave magnitude. Because the scale is logarithmic, a difference of one unit represents a tenfold difference in the magnitude of a seismic wave. For instance, an earthquake measured as 6.0 on the Richter scale is 10 times more intense than a 5.0 earthquake. A 7.0 earthquake is 100 times more intense than the 5.0 earthquake.

The Richter scale is still often cited in news reports of earthquakes, but scientists studying these events use another scale that allows for more accurate measurements. This is called the moment magnitude scale and it can be applied to a wider range of types and sizes of earthquakes. It is logarithmic, like the Richter scale, and similar to the older scale for earthquakes up to about a magnitude of 8.0. For larger quakes, the moment magnitude scale begins to differ from the Richter scale and provides more accurate measurements.

The First Seismograph

The history of the seismograph is a long one. It dates all the way back to ancient China. A Chinese mathematician named Chang Heng invented and constructed the first seismograph in A.D. 132. The original seismograph only gave limited details about earthquakes. It consisted of a large, bronze drum with eight dragons spaced around the outside edge. When the earth shook from an earthquake, a ball would drop from one of the dragon's mouths and fall into a bronze toad situated beneath it. The sound would alert an observer, and the particular dragon from which the ball fell would indicate the direction of the earthquake.

Fun Facts

Here are some fun facts about earthquakes:

To unlock this lesson you must be a Study.com Member.
Create your account

Register for a free trial

Are you a student or a teacher?
I am a teacher
What is your educational goal?
 Back

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back

Earning College Credit

Did you know… We have over 95 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it free for 5 days!
Create An Account
Support