When an earthquake occurs offshore, sometimes the result is a devastating wall of water that engulfs coastal areas. A tsunami is generated when a large area of the sea floor abruptly deforms and vertically displaces the water above it. As the water, which is under the influence of gravity, attempts to regain its equilibrium, it forms massive waves. Around the margins of the Pacific Ocean, where denser oceanic plates slip under continental plates in a process called subduction, the resulting earthquakes often cause tsunamis [source: University of Washington].
Today's scientists understand earthquakes a lot better than we did even 50 years ago, but they still can't match the quake-predicting prowess of the common toad (Bufo bufo), which can detect seismic activity days in advance of a quake. A 2010 study published in Journal of Zoology found that 96 percent of male toads in a population abandoned their breeding site five days before the earthquake that struck L'Aquila, Italy, in 2009, about 46 miles (74 kilometers) away. Researchers aren't quite sure how the toads do this, but it's believed that they can detect subtle signs, such as the release of gases and charged particles, that may occur before a quake [source: Science Daily].
Scientists can predict where major earthquakes are likely to occur, however, based on the movement of the plates in the Earth and the location of fault zones. They also can make general guesses about when earthquakes might occur in a certain area, by looking at the history of earthquakes in the region and detecting where pressure is building along fault lines. For example, if a region has experienced four magnitude 7 or larger quakes during the past 200 years, scientists would calculate the probability of another magnitude 7 quake occurring in the next 50 years at 50 percent. But these predictions may not turn out to be reliable because, when strain is released along one part of a fault system, it may actually increase strain on another part [source: USGS].
As a result, most earthquake predictions are vague at best. Scientists have had more success predicting aftershocks, additional quakes following an initial earthquake. These predictions are based on extensive research of aftershock patterns. Seismologists can make a good guess of how an earthquake originating along one fault will cause additional earthquakes in connected faults.
Another area of study is the relationship between magnetic and electrical charges in rock material and earthquakes. Some scientists have hypothesized that these electromagnetic fields change in a certain way just before an earthquake. Seismologists are also studying gas seepage and the tilting of the ground as warning signs of earthquakes. In 2009, for example, a technician at Italy's National Institute for Nuclear Physics claimed that he was able to predict the L'Aquila earthquake by measuring the radon gas seeping from the Earth's crust. His findings remain controversial [source: Joyce].
So, if we can't predict earthquakes, what can we do to prepare for them?