Earth Quakes and Associated Measuring Devices

Introduction: (Initial Observation)

Every year about 120 strong earthquakes with magnitude of 6 to 6.9 shake different areas of the United States. But the highest level of damage is from about 18 major earthquake that happen every year with magnitude of 7 to 7.9.

Scientists continuously record and locate the center of all earthquakes and are trying to find a pattern that may help them to forecast earthquake, days in advance.

Many different measuring devices and equipment are used for this purpose.

In this project you will study earthquakes and devices used to record it.

Information Gathering:

Study about the earth and tectonic plates. Find out about the movements of tectonic plates that ultimately is one of the frequent causes of earthquakes. Find out how you can record different earthquakes. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.

Following are some sample information that you may find in geology books.

Earthquakes are the Earth’s natural means of releasing stress. When the Earth’s plates move against each other, stress is put on the lithosphere. When this stress is great enough, the lithosphere breaks or shifts.

There are many different types of earthquakes: tectonic, volcanic, and explosion. The type of earthquake depends on the region where it occurs and the geological make-up of that region. The most common are tectonic earthquakes. These occur when rocks in the earth’s crust break due to geological forces created by movement of tectonic plates. Another type, volcanic earthquakes, occur in conjunction with volcanic activity. Collapse earthquakes are small earthquakes in underground caverns and mines, and explosion earthquakes result from the explosion of nuclear and chemical devices. We can measure motion from large tectonic earthquakes using GPS because rocks on either side of a fault are offset during this type of earthquake.

A force can be thought of as a push or pull. Force has both magnitude and direction, therefore it is a vector. From physics and Newton’s 2nd law, we know that force is equal to a change in an object’s momentum (mass x velocity) which describes the quantity of motion. Often, in the discussion of geology and earthquakes we use terms that describe force and the result of force on the Earth. When a force is applied to an object, the object is said to be under stress. Stress is the deforming force per area. Stress produces strain, the actual deformation. Stress and strain are related, so it is easy to determine one from the other if you know the value of proportionality, a constant value that relates strain to stress, of the substance that is being deformed (different for each individual material.)

Earthquake Severity

How Are Earthquakes Studied?

Seismologists study earthquakes by going out and looking at the damage caused by the earthquakes and by using seismographs. A seismograph is an instrument that records the shaking of the earth’s surface caused by seismic waves.

The First Seismograph

For centuries different societies have designed many creative ways to measure the shaking of the earth. Nearly 2000 years ago, for example, the ancient Chinese made a special vase that had several sculpted dragons mounted all around the sides of the vase. Each dragon held in its mouth a metal ball. When the ground shook, some of the balls would fall from the mouths of the dragons into the waiting mouths of the sculpted frogs to show the direction ground had moved.

Chang Heng’s “earthquake weathercock”
(From Walker, 1982)

Modern Seismographs

Today geologists measure earthquake waves with a seismograph. A typical seismograph works in a very simple way:
A heavy weight is fastened to a horizontal rod as shown in the diagram. This rod hangs from a pole ( and is free to swing from side to side when the ground shakes. At the other end of the rod (away from the pole) is an ink pen, and directly underneath the pen is a piece of paper rolled around a cylinder . This cylinder rotates so that the pen continuously draws an ink line along the moving paper. If the ground does not move, the rod does not swing, and the pen stays in place, so the ink line is smooth and straight. If the ground shakes, however, the row swings and so the pen draws a zigzag line as the paper turns. The stronger the shaking, the sharper the zigzags. This zigzag picture made on the paper roll is called a seismogram.

How a seismograph works?
counterweight remains steady,
seismograph moves with the earthquake,
Pen attached to the counterweight draw graphs representing the earthquake.

How Do I Read a Seismogram?

When you look at a seismogram, there will be wiggly lines all across it. These are all the seismic waves that the seismograph has recorded. Most of these waves were so small that nobody felt them. These tiny microseisms can be caused by heavy traffic near the seismograph, waves hitting a beach, the wind, and any number of other ordinary things that cause some shaking of the seismograph. There may also be some little dots or marks evenly spaced along the paper. These are marks for every minute that the drum of the seismograph has been turning. How far apart these minute marks are will depend on what kind of seismograph you have.

So which wiggles are the earthquake? The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records. The next set of seismic waves on your seismogram will be the S waves. These are usually bigger than the P waves.

If there aren’t any S waves marked on your seismogram, it probably means the earthquake happened on the other side of the planet. S waves can’t travel through the liquid layers of the earth so these waves never made it to your seismograph.

The surface waves (Love and Rayleigh waves) are the other, often larger, waves marked on the seismogram. Surface waves travel a little slower than S waves (which are slower than P waves) so they tend to arrive at the seismograph just after the S waves. For shallow earthquakes (earthquakes with a focus near the surface of the earth), the surface waves may be the largest waves recorded by the seismograph. Often they are the only waves recorded a long distance from medium-sized earthquakes.

How Are Earthquake Magnitudes Measured?

The Richter Scale

The magnitude of most earthquakes is measured on the Richter scale, invented by Charles F. Richter in 1934. The Richter magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake, no matter what type of wave was the strongest.

The Richter magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the Richter scale, the energy released by the earthquake goes up ten times. Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake (and 32 times as much energy would be released). To give you an idea how these numbers can add up, think of it in terms of the energy released by explosives: a magnitude 1 seismic wave releases as much energy as blowing up 6 ounces of TNT. A magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT. Pretty impressive, huh? Fortunately, most of the earthquakes that occur each year are magnitude 2.5 or less, too small to be felt by most people.

How Do I Locate That Earthquake’s Epicenter?

To figure out just where that earthquake happened, you need to look at your seismogram and you need to know what at least two other seismographs recorded for the same earthquake. You will also need a map of the world, a ruler, a pencil, and a compass for drawing circles on the map.

Here’s an example of a seismogram:

One minute intervals are marked by the small lines printed just above the squiggles made by the seismic waves (the time may be marked differently on some seismographs). The distance between the beginning of the first P wave and the first S wave tells you how many seconds the waves are apart. This number will be used to tell you how far your seismograph is from the epicenter of the earthquake.

Finding the Distance to the Epicenter and the Earthquake’s Magnitude

1. Measure the distance between the first P wave and the first S wave. In this case, the first P and S waves are 24 seconds apart.
2. Find the point for 24 seconds on the left side of the chart below and mark that point. According to the chart, this earthquake’s epicenter was 215 kilometers away.
3. Measure the amplitude of the strongest wave. The amplitude is the height (on paper) of the strongest wave. On this seismogram, the amplitude is 23 millimeters. Find 23 millimeters on the right side of the chart and mark that point.
4. Place a ruler (or straight edge) on the chart between the points you marked for the distance to the epicenter and the amplitude. The point where your ruler crosses the middle line on the chart marks the magnitude (strength) of the earthquake. This earthquake had a magnitude of 5.

Finding the Epicenter

You have just figured out how far your seismograph is from the epicenter and how strong the earthquake was, but you still don’t know exactly where the earthquake occurred. This is where the compass, the map, and the other seismograph records come in.

1. Check the scale on your map. It should look something like a piece of a ruler. All maps are different. On your map, one centimeter could be equal to 100 kilometers or something like that.
2. Figure out how long the distance to the epicenter (in centimeters) is on your map. For example, say your map has a scale where one centimeter is equal to 100 kilometers. If the epicenter of the earthquake is 215 kilometers away, that equals 2.15 centimeters on the map.
3. Using your compass, draw a circle with a radius equal to the number you came up with in Step #2 (the radius is the distance from the center of a circle to its edge). The center of the circle will be the location of your seismograph. The epicenter of the earthquake is somewhere on the edge of that circle.
4. Do the same thing for the distance to the epicenter that the other seismograms recorded (with the location of those seismographs at the center of their circles).

All of the circles should overlap. The point where all of the circles overlap is the approximate epicenter of the earthquake.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to learn about different types of earthquake and answer these questions:

1. How does earthquake affect buildings and heavy objects on the ground?
2. How can we record earthquake?
3. Can one device record earth quakes in any direction?
4. How can you know the magnitude of an earthquake?
5. How can you know the direction of an earthquake?
6. How can you locate the center of an earthquake?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variables for seismograph experiment are the direction, amplitude and the speed of earth movements. Dependent variable is the movements of seismograph and it’s resulting action (varies based on the design of seismograph).

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis.

I think any free floating weight attached to a pen can be used as a seismograph to record some kind of earthquake. Since earthquake can have different directions, we can not use one seismograph to record all different earthquakes. We need to have at least three seismographs to record the earth movements in 3 directions.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Design an experiment to show how does earthquake affect buildings and heavy objects on the ground?

Procedure:

1. Place a stone or any other heavy object on the center of a tray.
2. Hold the tray horizontally with two hands.
3. Move the tray to the left and write to simulate an earthquake with horizontal movements of the earth surface.

What happened?

Hint: When you shake the tray, the heavy object tends to stay at the same place. So tray will slide under the object. The fact that heavy objects tend to stay at the same place while the ground is shaking can be used to make s seismograph.

Experiment 2:

Make a Chinese earthquake detector to record the direction of the earthquake.

Procedures:

In this experiment you will use marbles or glass balls to make a Chinese earthquake detector. you need to make small ball holders and mount them around the vase (or any other round object) in a way that shaking the ground result falling some balls. ball holders are like small armchairs, so the balls will not fall from the back or from the sides.

Ball holders have a slope toward the vase so the balls will not fall by themselves or by wind.

You can use wood, cardboard or plastic tubes to make different ball holders. Use four or 8 ball holders around the vase.

Under each ball holder you may mount a small plastic cup or film canister to catch the fallen balls.

Place your Chinese earthquake detector on a table and shake the table. Which balls fell when you shook the table? Can you know the direction of table move by the fallen ball?

Experiment 3:

Make a model seismograph to record the horizontal movements of the earth in an earthquake. We call it a model, because what we make at home with limited access to material and tools, can not be a high precision and fully functional seismograph.

Introduction:

Model seismograph demonstrates basic components & principles of an actual seismograph used to record earthquake shock waves…Recorder is attached to a weight suspended from a support…Support moves with vibrations, but recorder remains stationary due to its inertia…Vibrations are then recorded on a strip of paper as it is pulled through recording frame…Simulate earthquakes by vibrating the table…Lesson plan included.

Here’s a simple diagram of a build-it-yourself seismograph:

A seismograph is a device that detects movements in the Earth’s surface, like earthquakes. The most important part of a seismograph is a pencil, loosely suspended over a roll of paper. If the ground starts shaking, the pencil will shake too. Since the pencil is being held over paper, it will make a line as it moves. So the more of a line you get, the more the pencil is moving, and the more the ground is shaking.

(http://www.loretto.org/middle/builda.htm)

You can also try looking at this Build Your Own Seismograph link… they have some really good explanations, instructions, pictures, etc.

Procedure:

1. Get a piece of wood about 16″ long (40 cm) to be the base for constructing a seismograph.
2. On one end of the wood surface mount an upright wood about 8 inches tall. This will be the main column. Note that there will be too much pressure on this wood, so ignore the right image and use a stronger wood.

3. Insert a nail or eye screw on the top of the post for connecting the suspension string.

4. Get a wood dowel or wooden stick about 10 inches long to be the horizontal arm or suspended arm of the seismograph. Make a hole on one end of this wood towel that will be toward the main column. Insert a needle or small nail in this hole. The other end of the nail enters a dimple on the main column. Also insert a nail or eye screw close to the other end, where you will connect a cord. This cord will keep the horizontal arm in suspension.

5. Connect the suspension string (or wire) between the eye screw above the main column and the eye screw on the suspended arm. Adjust it so the arm will stay horizontal. The suspended end of the arm can be slightly higher than the hinged side of the arm.

6. Attach a weight to the arm as close as possible to the suspended side, where you will install the pen. The weight can be any heavy metal or stone.

7. Connect a pencil to the suspended side for drawing graph.

As you see in the image, I had to use another piece of wood with a hole on that to hold the pencil. How you do it depends on what you can find around.

8. Place a paper under the pen and start to move your seismograph for test and final alignments. Make sure that the pen or pencil can draw lines.

9. Slowly pull the paper while shaking your seismometer to simulate drawing graph on a role of paper.

Experiment 4:

Make a seismograph to record the vertical movements of the ground in an earthquake.

Unlike seismograph in previous experiment that was a suspended weight designed for horizontal movements, this seismograph has a suspended weight for vertical movements. The main column is L shape on the top, so you can hang a spring. The other end of the spring as connected to the horizontal bar. Also the horizontal bar is connected to the main column by a hinge. What you see in the right is a diagram, not a final design.

You need to use this diagram and make your own design based on the material that is available to you. For example the horizontal bar can be a ruler stick and the weight can be a stone connected to the wooden stick by tape. The pen also can be connected to the wooden stick by masking tape.

A hole on one end of wooden stick can make a hinge. Pass a nail through the hole into the side of the main column to secure the horizontal bar. The spring can be substituted by a rubber band. Rotating drum is a role of paper.

To test your new seismograph hold it in your hands and move it up and down. Does it make any lines on the role or sheet of paper? Is there any relation between the size of lines and how hard you move the seismograph?

Experiment 5:

Make an improved version of Chinese earthquake detector to record the direction and magnitude of the earthquake.

This is similar to the previous Chinese earthquake sensor that you made in experiment number 2. The only difference is that you make two or three different levels of ball holders. One level or row of ball holders around the vase have a very small slope, these balls fall by a weak earthquake. Second row has ball holders with a higher slope. These balls fall with medium size earthquake. The third row has ball holders with the most slope. These balls fall only by strong earthquakes.

In this way by the number of fallen balls in each side, you will know the strength of the earthquake.

Materials and Equipment:

List of material can be extracted from the experiment section and must be updated based on your changes in design.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculation is required, however it is important to know how the magnitude of the earthquake is measured in Richter scale. This is described in the gathering information section.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Earthquakes are one of the most powerful natural forces that can disrupt our daily lives. There are many more questions about earthquake that can be the subject of research by geologists. Some of such questions are:

Why do earthquakes occur?
Why do some locations such as California and Japan receive so many earthquakes?
Can earthquakes be predicted?
Can we design a city to better withstand an earthquake?
Can we stop earthquakes before they occur? Should we try?

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Types of Earthquake: http://www.allshookup.org/quakes/wavetype.htm

A Demonstration of Seismology: http://jjlahr.com/science/earth_science/tabletop/