40. It was early morning, January 17, 1994. Jim and his wife Alicia were asleep in their house in Northridge, California. Suddenly, the loudest thunder they'd ever heard seemed to explode right through the ceiling, the floor, and the walls. They were thrown onto the floor. The dresser, on the other side of the bed, crashed onto the bed, which was shaking and bouncing violently. Paintings and a mirror flew off the bedroom walls. Their bedroom windows broke and the walls cracked as the foundation of the house moved.

Their cat took off through a window and didn't return for three days. Their two dogs covered their heads with their paws. Jim and Alicia scrambled to pick up the dogs and get out of the house, fearing that the roof and walls were going to collapse on them. They breathed easier once outside and saw their neighbors also running out of their houses. Jim and Alicia were only a half mile from the epicenter of the earthquake. Despite the wreckage to their home, which they had just bought, they considered themselves lucky just to be alive. They thought at first that they had just lived through the Big One, the one that scientists had said for years was going to destroy much of the Los Angeles area. But this wasn't the Big One. It was big, but not nearly as big as the one that's yet to come.

The Northridge quake was "only" 6.8 on the Richter scale (10 is maximum). There have been many earthquakes stronger than the Northridge one. The strongest quake ever recorded, 9.5, occurred in Chile in 1960. An earthquake in the Indian Ocean in December 2004 produced a tsunami that traveled at over 300 mph to hit Indonesia, Sri Lanka, India, Thailand, and neighboring countries, killing 230,000 people. The underwater earthquake was measured at 9.0, and it produced as much energy as 1,000 atomic bombs.

Each whole number on the Richter scale equals ten times the energy of the previous number. That is, a 3.0 quake is ten times as powerful as a 2.0 quake. Quakes are measured on instruments called seismographs.

Earthquakes usually occur where tectonic plates meet. About 30 of these plates cover the Earth. They are several miles thick and huge in area—most of the Pacific Ocean sits on just one plate.

Earthquakes occur when one plate strikes another or slides beneath another. Either action produces a huge amount of energy that travels upwards to the surface of the land or upwards to the surface of the ocean floor. A powerful ocean earthquake produces a tsunami, a fast‐moving wave that can be anywhere from a few feet high to as much as 100 feet high, as in 2004.

It is well known that various kinds of animals act oddly just before an earthquake occurs. Researchers hope to discover how these animals can actually detect an earthquake, and which animals are best at accurately detecting earthquakes. They'll use that knowledge to try to create an early warning system to save human lives. Humans will never be able to take the power out of an earthquake, but maybe someday, with the help of animals and technology, they can take the surprise out. 8.1, 540