The goal of earthquake prediction is to give early enough warning. The U.S. Geological Survey conducts and supports research on the likelihood of future earthquakes. Scientists estimate earthquake probabilities in two ways: by studying the history of large earthquakes in a special area and the rate at which strain（拉力）accumulates（积累）in the rock.
Scientists study the past frequency of large earthquakes in order to determine the future likelihood of similar large shocks. For example scientists researched the large earthquakes in the San Francisco Bay region during the 75 years between 1836 and 1911. For the next 68 years, no earthquakes of magnitude (震级) 6 or large occurred in the region. Beginning with a magnitude 6 shock in 1979, the earthquakes in the region increased dramatically; between 1979 and 1989, there were four magnitude 6 or greater earthquakes, including a magnitude 7.1 earthquake. So scientists estimated that the probability of a magnitude 6.8 or larger earthquake occurring during the next 30 years in the region is about 67 percent.
Another way to predict earthquakes is to study how fast strain accumulates. When plate movements build the strain in rocks to a critical level, like pulling a rubber band too tight, the rocks will suddenly break and slip to a new position. Scientists measure how much strain accumulates along a fault (断层) each year, how much time has passed since the last earthquake, and how much strain was released in the last earthquake. This information is used to calculate the time required for the accumulating strain to build to the level that results in an earthquake. This simple model is so complicated that such detailed information about faults is rare. In the United States, only the San Andreas Fault System has adequate records for using this prediction method.
Scientific understanding of earthquakes is of vital importance to the Nation. As the population increases, expanding urban development and construction encroach (侵蚀) upon areas susceptible(易受影响的) to earthquakes. With a greater understanding of the causes and effects of earthquakes, we may be able to reduce damage and loss of life from this destruction.
小题1:What does the passage mainly talk about?
| A．What an earthquake is like. |
| B．How to predict earthquakes. |
| C．Where earthquakes often happen. |
| D．When a fault is formed. |
小题2:That scientists study the history of large earthquakes in certain areas is to ultimately_________.
| A．do research on the past frequency of large earthquakes |
| B．estimate the magnitude of similar earthquakes |
| C．forecast the possibilities of similar earthquakes |
| D．judge the specific location of future earthquakes |
小题3:Which is TRUE according to the passage?
| A．There were four magnitude 6 earthquakes in the San Francisco Bay region between1979 and1989. |
| B．The accumulating strain of the fault to a certain level results in the earthquake. |
| C．About 68 years after 1911, no earthquakes occurred in the San Francisco Bay region. |
| D．The fast increasing population on the earth is the main cause of the earthquake. |
小题4:What is the critical factor of forming a fault?
| A．The material of rocks. |
| B．The existing time span of the rocks. |
| C．The plate movements around the rocks. |
| D．The amount of strain released in the last earthquake. |
小题5:According to the passage, we can know that the San Andreas Fault System____.
| A．has a greater understanding of the causes and effects of earthquakes |
| B．stores much more information about the history of large earthquakes |
| C．offers the potential for doing research on the faults where strain accumulates |
| D．illustrates specifically how rocks along a fault are formed |
