At sea-floor spreading ridges, hot magma rises up, cools and solidifies. These rocks then split and move apart as yet more magma rises, cools and solidifies. Over time, the rocks are moved great distances (tens or hundreds of miles) from the spreading ridges. The rocks close to the ridges were deposited recently (they are “young”), but the rocks far from the ridge were deposited long ago and then moved away slowly (they are “old”). , Points Earned: , 1/1 Your Response: , A 8., Most earthquakes:, A., Are caused when rocks on opposite sides of a break, or fault, in the Earth’s crust move in the same direction at the same speed. B., Are caused when rocks on opposite sides of a break, or fault, in the Earth’s crust move in different directions, and the fault is poorly lubricated, so the rocks along the fault get stuck for a while and bend their neighbors before breaking free and moving.C., Are caused when rocks on opposite sides of a break, or fault, in the Earth’s crust move in different directions, and the fault is well-lubricated all the time so the rocks can move freely.D., Are caused by Diet Coke drinkers kicking Pepsi machines at Penn State.E., Are caused by “implosion” of minerals taken to great depth in the Earth by tectonic processes. There may be “implosion” earthquakes, but they are rare. Some breaks in the crust are well-lubricated and don’t make earthquakes. If rocks on opposite sides of a break move in the same direction at the same speed, then there will be no relative motion between those rocks, and they won’t make earthquakes. But when rocks try to move in opposite directions but are stuck, they bend like springs and then break, shaking things and knocking them down in an earthquake. And Diet Coke drinkers who have not yet had their caffeine are unlikely to be sufficiently agitated to kick the Pepsi machines hard enough to make the larger earthquakes that are observed. , Points Earned: , 1/1
Your Response: , B 9. , On the Richter scale of earthquake intensity: , A. , The ground is shaken 10 times more by a magnitude-6 quake than by a magnitude-5 quake. B. , The ground is shaken twice as much by a magnitude-2 quake as by a magnitude-1 quake. C. , A magnitude-7 quake is impossible; nothing that big can occur. D. , The ground is shaken 5 times more by a magnitude-5 quake than by a magnitude-1 quake. E. , The ground is shaken 10 times more by a magnitude-5 quake than by a magnitude-6 quake. One problem in describing earthquakes is that the ground shaking in the smallest one you can feel is 1,000,000,000 times smaller than the ground shaking in the largest quakes. We usually dislike having a scale that requires us to talk about an event of, say, size 100,000,000; instead, if a magnitude-1 quake moves the ground 10 units (say, 10 nanometers at some specified distance from the quake), than we say that a magnitude-2 quake moves the ground 100 units, and a magnitude-3 quake moves the ground 1000 units, and so on. You’ll notice that the magnitude is just the number of zeros after the 1; this is a logarithmic scale.
You've reached the end of your free preview.
Want to read all 753 pages?