A series of small earthquakes have shaken central Nebraska and become the talk of the area. According to the information on a website, there have been several quakes since the 9th this month in the heart of the state, centered on the town Arnold, which is about 225 miles west of the capital Lincoln. The first, a 3. 3-magnitude(震级) quake, happened early that morning, followed by three on the following day, another on Sunday, and then the most recent earthquake on Monday. The strongest quake was the first one that struck on the 10th, which reached a magnitude of 3. 7. The earthquakes were found about three miles below the surface. There haven't been any reports of human injury or damage of buildings caused by the quakes, according to KWBE, a radio station.
"It is just kind of strange, " Becky Dailey, treasurer of the Arnold Chamber of Commerce, told that station, adding that people around town are running around and talking about the quakes. Actually small quakes like these are not unusual. Just two minutes before Nebraska's most recent earthquake, a separate one shook a city in the Dominican Republic, reaching a magnitude of 2.5. A couple of hours later, a 2. 7-magnitude earthquake hit an area near Aguanga, in Southern California's Riverside County. There were two more that day in different areas of Puerto Rico: a 2. 9-magnitude quake and a 3. 1-magnitude quake. Those were all small, but stronger quakes regularly rock the world—just not so often.
Earthquakes are usually caused when rock underground suddenly breaks. This sudden release of energy causes the waves that make the ground shake. Two blocks of rock or two plates are rubbing(摩擦) against each other. After a while, the rocks break because of all the pressure that is built up. When the rocks break, the earthquake happens.
