may only mean another big one is building up - instead of releasing pent-up energy with frequent, small shocks, as does the Ossipee, New Hampshire region. If a quake like the one of 1755 struck Cape Ann again, the damage could be substantial - especially in downtown Boston.

Although there has been no repeat of the shock of 1791, earthquakes still occur in Moodus. During 1981 and 1982, a swarm of quakes shook the region more than 500 times in the course of several months. Almost all of these tremors were tiny micro-quakes too small to be felt, except by sensitive instruments. The most recent moderate-to-large earthquakes occurred in February and March of 1917 and on November 3, 1968, shaking houses and rattling windows.¹⁷ Although activity over the past few years has been subdued, the potential remains for another moderate quake, or even a repeat of 1791.

Earthquakes are caused by the shifting of sections of the Earth's crust along faults, fractures that break up large sections of bedrock into separate units. Faults are like the cuts in a pizza all sliced up and ready to eat. The forces acting on the crust cause sections of bedrock to slide past each other along faults, in much the same way that someone pulls a slice out of a pizza. As slices of bedrock slide by, they bump and grind along their edges, releasing noises and causing the shocks we feel as earthquakes. Faults with lateral pizza-slice motion are called "strike-slip faults ' " In addition, two other types of motion can occur. When two blocks of crust move toward each other, one block is shoved on top of the other along a "thrust fault" (sometimes called a "reverse fault"). If the Earth's crust becomes stretched, a block may separate and drop downward along the third class of faults, "normal faults.'

Some faults are very small and extend for only a few hundred feet; others go for hundreds or even thousands of miles. Probably the best-known fault in this country (and also one of the largest in the world) is the San Andreas Fault of California, a huge strike-slip fault. Movement of two large sections of crust past each other along the San Andreas is responsible for the many earthquakes of that region, including the famous 1906 quake that devastated San Francisco. People often joke that California will fall into the ocean some day, but the actual state of affairs

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