Karen Lambert, age 13, of St. Louis, Missouri, for her question;

Do earthquakes always follow the same lines?

First, Andy wishes to thank Karen and many other pen pals who asked about his safety during California's recent earthquake. He suffered no harm, though aftershocks insisted on shaking his surroundings for a month or more. Actually, he lives about 50 miles from the epicenter, where disaster struck. But a quake of that magnitude is felt for hundreds of miles in all directions. Some of Andy's books leaped off the shelves and his favorite toadstool got slightly bruised. Thank you all for hoping that he and his helpers were safe.

We know that earthquakes tend to occur along certain fault lines in the earth's crust. But as a rule, these faults are not single crustal cracks. They occur in weak crustal areas where massive blocks resemble the fragments of a shattered tile. Where there is one earthquake fault, usually there are others. It may be more accurate to call such a region an earthquake zone. Such a zone exists below the rich valleys, the golden slopes and mountains of California.

Here, the central troublemaker is the San Andreas fault that runs from Mexico up through California and into the floor of the North Pacific. This major fault marks the severance between two enormous crustal blocks. In the general pattern of earth motions, the block on the seaward side is inching northwest. Seismologists say that if this trend continues for another 60 million years, Los Angeles will reach the vicinity of Alaska.

Every once in a while, a major earthquake occurs .at some point along the San Andreas fault. Each event shifts the crustal blocks a few feet along the way. No two earthquakes are exactly alike. But those that occur along the same fault line tend to repeat similar patterns. However, in a restless crustal zone of this type, many other motions occur almost continuously on both sides of the major fault line.

Through the ages, dozens of large and small fractures crack deep    into the crust. Most of them run parallel to the major fault and many are separated by masses of shattered rock..

A major earthquake zone is a network of countless fault lines. Since the entire region is on the move, tensions build up in various parts of the disjointed network. At present, seismologists cannot predict where or when the next line will release its stress with a shudder. For example, the California earthquake of February 9 occurred about ten miles below one of many bitsy fault lines. It runs crosswise to the major network and its tremors followed unexpected paths. However, the crustal motion followed the same general pattern of this restless zone.

Growing mountains are hoisted aloft with the help of earthquakes and erupting vol¬canoes. The world's youngest mountains are in the Coastal Range along our Pacific coast¬line. San Andreas and his fractured brethren contribute to their mountainous growing pains. However, the volcanic partners in the program subsided long ago. Now they enhance the scenery as splendid peaks, many of them capped with snow.