Seizing up the Quake: the Prediction by Trista L

Name ______Period _____

“Seising” Up the Shake of the Quake 1 It starts with a thud and ends with the ground rolling beneath you. Anybody who has experienced an earthquake will tell you how it starts does not matter. You never forget the actual quake. Seismologists and geologists, however, take great interest in how earthquakes begin. Why you ask? It is the prediction of earthquakes that can help save lives and millions of dollars in property damage.

2 When seismologists try to predict earthquakes, their goal is to produce a warning system. If scientists can develop accurate and early warning systems, then people would be able to respond quickly. So who are the scientists who research future earthquakes? The United States Geological Survey (USGS) carries out research and supports other researchers who focus on the occurrence of future earthquakes. Scientists with this group conduct field and laboratory studies of earthquakes and fault zones. Their goal is to improve the probability estimates of earthquakes. To estimate earthquake probabilities, seismologists study the history of large earthquakes in specific areas. They also study the rate of strain or stress that accumulates along the fault zones.

3 Seismologists and geologists study the past frequency of large earthquakes. They can then use this information to predict the probability of similar large quakes in the future. Let us say that Rattle County, California, had four earthquakes that were magnitude 7.0 or higher during the last 200 years. If these earthquakes occurred randomly, scientists might say there is a 50% chance of another magnitude 7.0 quake during the next 50 years. However, other factors can influence the prediction of future earthquakes.

4 It would be nice if earthquakes happened randomly. Most often, this is not the case. When an earthquake occurs, there is strain on the fault system. A strain results from force or pressure that causes the fault to change shape or fracture. Strain on one part of the system can increase the strain on another part of the system. Let us visit Rattle County again. During seventy-five years between 1800 and 1875, Rattle County had four earthquakes that measured a magnitude of 6.8 or higher. There were also many 6.0 to 6.5--magnitude quakes. Rattle County was major earthquake-free until 1980. In 1981, Rattle County had an earthquake that measured 6.0. The quake was the beginning of a lot of seismic activity in Rattle County. Over the next ten years, Rattle County had four earthquakes that measured 6.0 or higher. Seismologists can use this clustering or group of earthquakes to predict future earthquakes for Rattle County. In fact, scientists may have estimated that there was a 67% chance that an earthquake that measured 6.8 or higher would occur during the next thirty years in Rattle County.

5 Seismologists also study fault strains. They look at how fast a strain accumulates along a fault. Since the earth's plates move continuously, strain accumulates or builds along the plates fault lines. When the strain builds to an extremely high level, the rocks along the fault will break suddenly. These rocks will also slip into a new position. Seismologists look at the amount of time that has passed since the last earthquake along that fault; the amount of strain that has built up along that fault; and the amount of strain that was released during the last earthquake. These scientists then use this information to calculate the time it will take for the same amount of strain to build up along the fault. However, there is one tiny problem. It is difficult for seismologists and geologists to collect this type of specific information about fault strain. The only fault system that has enough information for scientists to use this type of prediction method is the San Andreas fault system in California, U.S.A.

6 Scientists have used prediction methods and monitoring instruments to study the San Andreas fault line. They have found out that for the last 150 years there have been earthquakes (magnitude 6.0) that have occurred an average of every 22 years. Since the last "shock" occurred in 1966, (Parkfield, California), seismologists have tried to monitor and experiment with prediction methods along the fault. This experiment is called the Parkfield Earthquake Prediction Experiment. The goal of this experiment has been for scientists to record seismic changes before and after the expected earthquake; to issue a short-term prediction; and to develop effective methods for warning about potential earthquakes. In "Seising" Up the Quake: The Measurement, we will look at how seismologists measure the earth's seismic activity.

"Seizing" Up the Quake: The Prediction

1. The United States Geological Survey carries out 2. Fault strain is not used to help scientists predict research on the ______. future earthquakes. A.Occurrence of future volcanic eruptions False B. Occurrence of future earthquakes True C. Occurrence of tsunamis D. None of the above 3. It is difficult to predict earthquake activity along 4. How does a strain occur along a fault system? fault lines because ______. A. It is difficult to record past earthquake activity B. It is difficult to measure consistently measure strain on fault lines C. A and D are both correct D. It is difficult to collect specific information about fault lines 5. The Parkfield Earthquake Prediction Experiment 6. To estimate the probability, scientists study ______. focuses on studying activity along the San Andreas A. Past earthquake history and accumulated strain fault and predicting future earthquakes along that along fault lines fault. B. Past earthquake history False C. Casualties from earthquakes True D. Property damage from earthquakes 7. Earthquakes always happen in random patterns. 8. How do scientists use the amount of time that has False passed between earthquakes to help them predict True future earthquakes?

Name Date ______

"Seizing" Up the Quake: The Prediction Seismologists are continually looking for ways to predict future earthquakes. Use what you know about earthquakes to write a proposal for a new experiment that will focus on earthquake prediction.

"Seizing" Up the Quake: The Prediction - Answer Key

1 Occurrence of future earthquakes 2 False 3 A and D 4 As the earth's plates continuously move, they exert a force on the fault line and the rocks that surround the fault line. The force causes strain to build up along the fault line and surrounding rocks. Once the strain reaches an extreme point, the rocks fracture and move into new positions. 5 True 6 Past earthquake history and accumulated strain along fault lines 7 False 8 Seismologists look at the amount of time that has passed between major earthquakes in an area. They use this information along with the strain that was produced during that earthquake and the amount of strain that has built up to predict future earthquakes.