单选题
For anyone who has experienced an earthquake, the experience can be frightening and traumatic. In addition of the movement of the ground, people need to concerned with collapsing buildings and falling debris, such as flying glass. The majority of the injuries and death that occur from the earthquakes are due to falling objects and structures. The effect of an earthquake can also cause dangerous landslides, fires, gas line explosions and flood-waters from collapsing dam. The goal of seismologists is to understand the earthquake and other seismic activity on Earth. This information, when shared with people in earthquake prone areas, can help decrease the number of deaths and injuries that may occur. One of the most destructive effects of earthquake is tsunami. Tsunami, giant ocean waves, from after an earthquake has occurred on the ocean floor. If the tsunami crashes into land, it may cause destruction. The difficulty with protecting people from tsunami is that they may come without warning and at an extremely high speed. Once undersea earthquakes occur, the ocean floor rises and sinks. This is when tsunami may begin to form. Along with this shifting of the ocean floor, there is also a large masses of seawater that may drop or rise. To adjust the sudden change in sea level, the mass of water moves upward and downward. As it is moving, a series of reactions come long. Low waves begin to move from the point of the epicenter outward. These waves will increase in height as they come closer to the shore. Underwater landslides caused by earthquakes may also form tsunamis. On land, the focus of an earthquake's destruction is usually buildings and property. Most of the buildings today are built using strict building codes. These codes require that the building can withstand the swaying motion of the ground during an earthquake. However, there buildings, like skyscrapers, may sway so violently that they may tip over and cause damage to lower structures nearby. One factor that affects the intensity of an earthquake is the local geology. The type of land that beneath the buildings can determine the way the buildings respond to an earthquake. Building that are constructed on loose soil and rock. Likely soil and rock vibrate as if they were jelly. When buildings are constructed on this type of land, they tend to have an exaggerated motion and to sway violently.