On October 17, 1989, baseball fans cheered the Dodgers and Giants at the World Series in San Francisco. Then, at 5:04, an earthquake struck. Loud rumbling filled the air, the ground wobbled, cement roads rippled as if they were made of water and the stadium cracked. Then 15 seconds later, the earthquake was over. Afterward, highways collapsed and buildings crumbled. About 90 people were killed, and more than $6 billion of property was damaged.
	A house in San Francisco after the quake.	Scientists figured out that this earthquake measured 7.1 on the Richter (“RIK-tur’) scale. The Richter scale is how scientists measure the amount of energy that’s released during an earthquake. An earthquake that measures 7 on the Richter scale releases 30 times more energy than one that measures 6. Most earthquakes are mild, usually less than 2 on this scale, so people don‘t even notice them. In fact, earthquakes happen every day somewhere on our planet.
		A section of highway collapses.