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# Natural Disaster: Earthquakes by Kathiann M. Kowalski

Just as the World Series game was to start on October 17, 1989, people at San Francisco's Candlestick Park felt a rumbling. It was an earthquake along California's San Andreas fault. The earthquake killed 67 people in the San Francisco Bay area.

Earthquakes occur most often near edges of tectonic plates. The edges are called fault lines. Plates slipping or scraping against each other release energy inside the Earth.

Earthquakes may last only a minute, but they can do tremendous damage. Thousands of people died in 1999 after major earthquakes struck Turkey, Greece, and Taiwan.

Scientists measure earthquakes with two scales. The Richter scale gauges how much energy was released at the earthquake's source. Each whole number on the Richter scale is a tenfold increase over the previous number. Level 2 is barely detectable. Level 6 is moderately destructive. Level 8 is total damage.

The modified Mercalli scale ranges from I through XII. It describes how an earthquake is felt at a specific place. Level I earthquakes are barely felt. Level VI earthquakes are felt by everyone.

If everything around you starts shaking and rumbling, duck and cover. Duck down under a desk or in a doorway. Cover your head with your arms. When the rumbling stops, get outside. Wait until an adult says the building is safe before going back inside.

## NATURE STATS

How Does Earth Measure Up?

The distance around the equator is 24,902 miles (40,075 km).Measuring around the poles, the distance is 24,860 miles (40,008 km).The distance from the North Pole to the South Pole through the center of the Earth is 7,900 miles (12,714 km).

Mass measures how much matter something has. Scientists have calculated Earth's mass at 6.0 × 1024 kilograms. That would be 6 followed by 24 zeroes, or six trillion trillion. No wonder the ancient Roman character Atlas looks so tired in pictures that show him carrying the world on his shoulders!

## IT'S A NATURAL FACT!

Hawaii: Built by Volcanoes

The Hawaiian Islands were built by volcanic action on the floor of the Pacific Ocean. Some of the islands' volcanoes are still active.

In fact, the island chain continues to change. Islands to the southeast are younger, geologically speaking. They are still growing.

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#### THE EVERYTHING KIDS' NATURE BOOK

By Kathiann M. Kowalski

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