Topic Seismographs measure the intensity of earthquakes.

Transcription

1 Earthquake Intensity Topic Seismographs measure the intensity of earthquakes. Introduction Scientists have been rating the intensity of earthquakes since the late 1700s. The instruments that measure earthquake activity, seismographs, record a zigzag trace that is made by ground movements. In 1783, Michele de Rossi and François-Alphonse Forel developed the 10-point Rossi-Forel Scale for measuring the intensity of earthquakes. More than 140 years later, Guiseppe Mercalli invented a 12-point intensity scale. In 1931, Harry Wood and Frank Neumann developed a measurement scale that is still used widely in the United States. These two scientists collaborated to devise the Modified Mercalli Intensity Scale, which is not based on math. In 1935 Charles Richter invented the well-known Richter Scale. This math-based measurement ranges from 1 to 10; each whole number increase on the scale represents a tenfold increase in amplitude. In this experiment, you will build a simple model seismograph and develop your own magnitude scale. Time Required 30 minutes Materials large textbook string (about 2 yards [yd] [approximately 2 meters (m)] long) pen tape several sheets of paper

2 EARTHQUAKE INTENSITY 2 small table or desk rubber band science notebook Safety Note Please review and follow the safety guidelines. Procedure 1. Tape a piece of paper to the top of a table or desk. 2. Tape the pen to the book so that the point of the pen extends beyond the edge of the book, as in Figure 1. tape Figure 1 3. Run the string through the center of the book so that an equal amount of string hangs from both sides. Tie the free ends of the string together. 4. Close the book and secure it shut with the rubber band. 5. Lift the book by the string and suspend it above the desk or table. Hold the book at a height that permits the point of the pen to touch the paper (see Figure 2). 6. Pull the book so that the pencil makes a line along the length of the paper. This line will serve as a baseline for your homemade seismograph.

3 EARTHQUAKE INTENSITY 3 string rubber band paper tape Figure 2 7. With your lab partner, record the intensity of five tablequakes. Tablequake 1 will be the mildest and tablequake 5 the most severe. To do so: Repeat step 6, but this time have your lab partner very gently shake the desk from side to side to simulate a mild earthquake. When your pen has traced the results of this quake, label the line as 1. Repeat this procedure four more times. Each time, make the tablequake more severe. 8. Compare your control line with the five lines produced by tablequakes.

4 EARTHQUAKE INTENSITY 4 Analysis 1. What was the purpose of drawing a control line? 2. What do the tablequake lines tell you about how hard the table was shaken? 3. Do individual lines have consistent degrees of jaggedness from start to finish? 4. How are the lines you drew similar to the lines on a real seismograph? 5. On a day when there is not any earthquake activity, what do you think the lines on a seismograph look like? Explain your reasoning. What s Going On? Seismographs have been used for centuries to measure seismic waves. They allow us to detect earthquakes and pinpoint the time of occurrence, location, and magnitude. Microquakes, very mild disturbances that register less than 2 on the Richter scale and are not noticeable to most people, occur constantly. If an earthquake measures between 2 and 6, it is considered to be moderate. Severe quakes, those above 6 on the scale, can be dangerous. Want to Know More? See Our Findings.

5 OUR FINDINGS EARTHQUAKE INTENSITY Suggestion for class discussion: Show students a film clip of an earthquake or ask if anyone in the class has ever been in an earthquake. From the film clip or description, ask students to describe the ways in which the earth s crust is displaced during an earthquake. Analysis 1. A control line allows you to see the result of no shaking and compare the no shaking line to the lines made after shaking the desk. 2. More jagged lines represent a harder shake. 3. No. The degree of jaggedness depends on the amount of shaking. 4. Lines on a true seismograph result from the Earth s shaking just as the lines in this experiment were made by the desk shaking. 5. Answers will vary. Small vibrations occur in the crust all of the time and can create small changes in the lines.

6 SAFETY PRECAUTIONS Review Before Starting Any Experiment Each experiment includes special safety precautions that are relevant to that particular project. These do not include all the basic safety precautions that are necessary whenever you are working on a scientific experiment. For this reason, it is absolutely necessary that you read and remain mindful of the General Safety Precautions that follow. Experimental science can be dangerous, and good laboratory procedure always includes following basic safety rules. Things can happen very quickly while you are performing an experiment. Materials can spill, break, or even catch fire. There will be no time after the fact to protect yourself. Always prepare for unexpected dangers by following the basic safety guidelines during the entire experiment, whether or not something seems dangerous to you at a given moment. We have been quite sparing in prescribing safety precautions for the individual experiments. For one reason, we want you to take very seriously every safety precaution that is printed in this book. If you see it written here, you can be sure that it is here because it is absolutely critical. Read the safety precautions here and at the beginning of each experiment before performing each lab activity. It is difficult to remember a long set of general rules. By rereading these general precautions every time you set up an experiment, you will be reminding yourself that lab safety is critically important. In addition, use your good judgment and pay close attention when performing potentially dangerous procedures. Just because the book does not say Be careful with hot liquids or Don t cut yourself with a knife does not mean that you can be careless when boiling water or using a knife to punch holes in plastic bottles. Notes in the text are special precautions to which you must pay special attention. GENERAL SAFETY PRECAUTIONS Accidents caused by carelessness, haste, insufficient knowledge, or taking an unnecessary risk can be avoided by practicing safety procedures and being alert while conducting experiments. Be sure to

7 SAFETY PRECAUTIONS 2 check the individual experiments in this book for additional safety regulations and adult supervision requirements. If you will be working in a lab, do not work alone. When you are working off-site, keep in groups with a minimum of three students per groups, and follow school rules and state legal requirements for the number of supervisors required. Ask an adult supervisor with basic training in first aid to carry a small first-aid kit. Make sure everyone knows where this person will be during the experiment. PREPARING Clear all surfaces before beginning experiments. Read the instructions before you start. Know the hazards of the experiments and anticipate dangers. PROTECTING YOURSELF Follow the directions step by step. Do only one experiment at a time. Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and first-aid kit. Make sure there is adequate ventilation. Do not horseplay. Keep floor and workspace neat, clean, and dry. Clean up spills immediately. If glassware breaks, do not clean it up; ask for teacher assistance. Tie back long hair. Never eat, drink, or smoke in the laboratory or workspace. Do not eat or drink any substances tested unless expressly permitted to do so by a knowledgeable adult. USING EQUIPMENT WITH CARE Set up apparatus far from the edge of the desk. Use knives or other sharp-pointed instruments with care.

8 SAFETY PRECAUTIONS 3 Pull plugs, not cords, when removing electrical plugs. Clean glassware before and after use. Clean up broken glassware immediately. Do not touch metal conductors. Check glassware for scratches, cracks, and sharp edges. Do not use reflected sunlight to illuminate your microscope. Use alcohol-filled thermometers, not mercury-filled thermometers. USING CHEMICALS Never taste or inhale chemicals. Label all bottles and apparatus containing chemicals. Read labels carefully. Avoid chemical contact with skin and eyes (wear safety glasses, lab apron, and gloves). Do not touch chemical solutions. Wash hands before and after using solutions. Wipe up spills thoroughly. HEATING SUBSTANCES Wear safety glasses, apron, and gloves when boiling water. Keep your face away from test tubes and beakers. Use test tubes, beakers, and other glassware made of Pyrex glass. Never leave apparatus unattended. Use safety tongs and heat-resistant gloves. If your laboratory does not have heat-proof workbenches, put your Bunsen burner on a heat-proof mat before lighting it. Take care when lighting your Bunsen burner; light it with the airhole closed, and use a Bunsen burner lighter in preference to wooden matches.

9 SAFETY PRECAUTIONS 4 Turn off hot plates, Bunsen burners, and gas when you are done. Have a fire extinguisher on hand. Keep flammable substances away from flames and other sources of heat. FINISHING UP Thoroughly clean your work area and any glassware used. Wash your hands. Be careful not to return chemicals or contaminated reagents to the wrong containers. Do not dispose of materials in the sink unless instructed to do so. Clean up all residues and put them in proper containers for disposal. Dispose of all chemicals according to all local, state, and federal laws. BE SAFETY CONSCIOUS AT ALL TIMES!