Barton Cliffton, age 11, of Montgomery Ala,,  for_ his question:

How long does an earthquake last ?

We are always shocked to hear news of a terrible earthquake, The reports tell us how the ground shook and thundered. Tall buildings rocked and tumbled. Gas pipes, water mains and telephone wires were ripped asunder and great tidal waves came rushing in from the sea, Chances are, we want to give a helping hand to the poor people hurt and made homeless in such a disaster area,

We may decide that the old earth is careless at such times. Maybe it is not to be trusted. Then we collect our thoughts and remember that most of the time, in fact almost ail of the times the good old earth is firm and steady beneath out feet, And we realize that it must be quite a job to beep the surface of the ground firm and steady   the great mountains from falling and the sea in its place.

Then we remember that day by day the weather is steadily

changing the surface of the earth. Tall mountains are gradually washed away into the seas. Sand and soil is shifted by wind and rain from place to place. All this earth moving is done so gently that only once in a great while do we notice the difference. Then we realize that the old earth is far from careless and very very much to be trusted,

The earth on which we live is shaped like a ball. Lines drawn from the center to the surface in any direction are almost the same length. And in order to keep this world of ours round, the weight of each pie slice section must remain equal.

The earth’s problem is to keep up with the changes of weight on its surface and redistribute it so that the crust is about the same weight all over. Sometimes a great slice of the earth's crust is much heavier than the slice next to it. Maybe a million years of weather have dumped a huge mountain range into an ocean floor. Or maybe a range of newly formed mountains is made of much lighter material than the ocean bed at its feet.

When this happens, we have a weak spot in the earth s crust, We have an earthquake area. For, from time to times the earth must shift and rebalance the weight of the crust. This is done way below ground level. Then, the people in these regions feel the ground tremble as great masses of rocks are heaved about below. Sometimes n huge chunk of material tumbles about and shakes the very ground above it. But all of this reshif ting is done in a great hurry. The old earth wastes no time in this sort of furniture moving. True, the destructive effects of an earthquake may last for many years. But the actual job of rock moving and earth shaking only lasts a few seconds. It is a very rare earthquake which lasts as long as one minute,