单选题 .  As scientists learn more about the causes of earthquakes, they become better able to predict them. First of all, they know that quakes are likely to occur in areas where the tectonic plates (地层地壳板块) push against each other. They study these areas closely, using different instruments. They measure the vibrations of the earth with seismographs (地震仪), which record on rolls of paper all movements, both large and small. Scientists usually use the Richter scale (里希特震级仪) named after a famous seismologist (地震学家), for these measurements. When an earthquake measures over 4～5 on the Richter scale, it is strong enough to cause damage. Scientists have determined that an area is not likely to have a large earthquake when many small quakes have been occurring. When the small quakes stop, then pressure builds and a strong quake is more likely.
    There are several other ways to predict earthquakes. Scientists can measure the tiny changes in the tilt (倾斜) of the land that happen before earthquakes occur. Increases in the amount of radon (氡), a substance found in deep wells, as well as a higher level of water in the wells, can also mean that an earthquake is likely to occur. In addition, scientists have found that some animals, like dogs, behave strangely before an earthquake, they become nervous and howl (号叫). Seismologists have correctly predicted several earthquakes. In 1975, they said that an earthquake would occur in Liaoning Province, China, one month, and then one hour, before it happened. In 1978, Russian scientists predicted an earthquake in the Altai Mountains six hours before it occurred. However, not all earthquakes are predictable, and a system for predicting is not yet perfected. Nothing on this earth is certain. Although people who live in California and Japan live with the possibility of a serious quake, perhaps the next strong earthquake will occur somewhere outside the "Ring of Fire".1.  According to the information in Para. 1 seismograph is ______.