Alan Cagle, age 12, of Bixby, Oklahoma; for his question:

How does a seismograph work?

Through the years; Andy has answered many questions about earthquakes. And each time he managed to sneak in this suggestion. The world needs many more seismology teams with lots of superior equipment and a chance to probe every detail that goes on in the restless crust of the earth. This logical step should, in time, give the know how required to predict when and where an earthquake is likely to happen. Until we tackle this basic seismology task in a big way; sudden earthquakes will continue to shake up crowded communities.

During the past months, serious earthquakes have shaken Peru and Italy, Alaska, Sumatra and other far flung regions around the globe. On February 9, a fairly serious one brought disaster to several crowded communities in southern California. This state tends to be earthquake prone because here the earth's crust has several major faults., plus a network of hundreds of minor ones. Earthquakes from major faults are expected, though not yet predictable. But February's shuddering shake was triggered by one of the minor faults.

Seismologists located in special stations keep records of earthquakes and watch their patterns on a global scale. A sensitive seismograph instrument measures the pulsing vibrations that an earthquake sends through the solid earth in all directions. Some vibrations take horizontal paths through the crustal shell. Other types take vertical paths and tangents down through the globe. A seismograph registers these vibration patterns and records them on graphs called seismograms.

Basically the sensitive instrument is a suspended weight, firmly anchored into a deep., massive foundation of rock or concrete. The sturdy foundation ignores everyday surface shakes, such as passing trucks. But it responds to earthquake vibrations and relays them to the suspended weight. The heavy weight tends to resist    and this causes its support to echo in harmony with the vibration pattern. An attachment records the details. This may be an automatic pen that lines a graph on a revolving drum. Or it may be a more accurate modern device that triggers an electromagnetic current, measured by a galameter. Abeam of reflected light marks this finely detailed seismograph on a photographic plate.

A seismology center has a priority communications system with other stations and at least three seismographs. One specializes in the north east vibration paths through the crustal shell, another in the east west horizontal paths. Another seismograph records and reports the complex patterns of the vertical vibrations that travel down through the globe.

All seismographs can report the duration and likely strength of an earthquake. But its epicenter and local magnitude cannot be figured from one station. This is pinpointed by triangulating evidence from several widely separated seismology stations. The complicated comparisons and computings begin at once, long before the aftermaths of a major quake have gentled down to normal.