Earthquakes

April 18 , 1906 , California San Andreas ____________________ ____________________ , shaking San Francisco for nearly 60 ____________________ seconds . When the ____________________ stops , the disaster is only beginning . Gas lines ____________________ setting off massive fires . Some ____________________ people die . Most of the city is reduced to ____________________ .
This ____________________ of the ____________________ caused when masses of rocks suddenly ____________________ below the earth's surface is called an earthquake .
Hundreds of little earthquakes ____________________ the planet every day but most pass ____________________ . They usually occur along the boundaries of the thin ____________________ that cover the Earth like an ____________________ . Driven by the heat deep within the Earth's ____________________ , the plates ____________________ against each other along lines called ? faults ? . When a plate's ____________________ is blocked , stress builds up . Finally the fault ____________________ ____________________ . The released energy races through the Earth in the form of seismic ____________________ .
Scientists record these ____________________ on a device called a ____________________ . These zigzag lines show the ____________________ of various seismic ____________________ . Using the lines scientists ____________________ the earthquake on the Richter scale . For a quake to measure one number higher on the Richter scale it must ____________________ about 30 times as much energy as the number below it .
Every year , about ____________________ , ____________________ earthquakes ____________________ through the ground hard enough for people to feel them . Of these , only about ____________________ , ____________________ are strong enough to ____________________ ____________________ . But a powerful earthquake can be ____________________ . On average , about ____________________ , ____________________ people die each year as a result of earthquakes .
The greatest recorded earthquake ever to ____________________ North America measured a massive 9 . 2 . The ____________________ struck Alaska on March 28 , 1964 . A camera on board a ship docked in Valdez recorded the draining of the entire harbor as a ____________________ opened up on the sea ____________________ .
There's no stopping the surface of the Earth from ____________________ and ____________________ so engineers are focusing on ways to create better ____________________ , ____________________ and ____________________ , structures that will remain ____________________ and stay in one ____________________ the next time the Earth begins to shake .