 Out of the fog of a chilly morning's dawn, a great city shakes off sleep when drowsily comes to life. To begin another day like so many others in its history. And yet, the city lives with a constant threat, the remote but real possibility of a great disaster. On together, men and women from many places, many backgrounds, 700,000 people live here. First swells with a bustle of over a million. A specter walks these streets, shoulder to shoulder with the people. For San Francisco lives nearby one of the most severe earthquake faults in all the world. Team 72. A new kind of satellite leaps toward orbit. A satellite designed to keep an eye on the earth. Take its pulse and its picture. Satellite radios back vast quantities of data that enrich our understanding of subjects from pollution to mining. From fishing to farming to flood control. Could it as well help bring a better understanding of earthquakes? That was a subject for which the spacecraft held little promise, but time would tell a different story. The satellite looks down on an earth that is constantly changing as it has changed through all time. Enormous pressures from deep within shove against the earth's rocky crust. The ground gives way, bending to a new shape. And still the pressure continues until at last the rock splits apart, usually along an already weakened area called a fault line. Periodically, the people of California get a gruesome reminder of what can happen when the earth suddenly moves. San Francisco, 1906, 517 a.m. It's only been lately that scientists have begun to understand what an earthquake really is. Simply the shaking of the ground, this little escarpment I'm walking along here came into existence. Dr. Clarence Allen, professor of geology and geophysics at the California Institute of Technology tells of a recent quake. We can actually see down here, all my hand is, the actual fault plane. A fault plane that extends many miles down into the earth where the earthquake actually started. Now what causes earthquakes? This green strip represents a valley carved along the San Andreas Fault. And these three black strips represent three fences that were built across the fault many years ago. Fences which gradually become deformed or bent because of the horizontal movement of the valley walls at a rate of perhaps one or two inches every year. After years of movement, the rocks finally yield to the enormous stress and break apart. This is an earthquake. Earthquakes don't just happen on dry land. They happen as well on the ocean floor. Under the enormous stress until one section of the ocean floor springs suddenly upward. The water above it is thrust up the same way. This vertical wave erupts to the surface and begins racing toward shore at an alarming speed, up to 500 miles an hour. Nearing the shore where the ocean bottom climbs upward, the water begins to push upward into a giant wall, sometimes as high as a 10-story building. This is the dreaded tsunami, or tidal wave. Earthquakes have happened in every state of the United States, but the most vulnerable is California. The San Andreas Fault runs almost the whole length of the state, and another shorter one brackets the Bay Area of San Francisco. In addition to the major faults, there is a whole slew of lesser ones, an entire system of them. Any one could be the site of an earthquake. Scientists are racing against time to find a way of predicting when and where the next major quake will strike. There was no warning in 1971. San Fernando Valley outside Los Angeles. To know more about earthquakes, to discover the secret of predicting them in time to give warning. NASA is working to support earthquake research being done by the U.S. Geological Survey. The Landsat satellite, formerly called Earths, has been yielding some valuable new information. Brian, let's see if we can identify some of these faults you found on the aircraft imagery on Earths. All right, Bob, on the aircraft image, we've got about three miles of a fault here. If we look at this on the Earth's image, we can extend it to about 60 miles. The more exciting is one down here on the Earth's image, a very major structure cuts across the whole mountain range. We've never known about it before until we have the Earth's image. Entire fault systems revealed for the first time by satellite. Knowledge like this may one day help to save many thousands of lives. Satellites are playing another even more important role in earthquake research in this NASA project toward developing a prediction capability. Two stations like this have been erected 500 miles apart on opposite sides of the San Andreas Fault. From each station, a laser beam is aimed at a satellite overhead and the reflected signals picked up. Because the satellite position is known very accurately, the researchers can compute the distance between the two ground stations with great precision. Comparing the readings over a period of time, they should be able to determine how much the ground is moving and how fast. In another project, NASA researchers are using radio signals from quasar stars outside our galaxy to detect these minute Earth movements. Scientists hope that applying space technology to this Earthly problem may one day enable them to say, here the stress has reached its limit. Here about such and such a day, an earthquake will occur. But today, no one can say when an earthquake might rumble San Francisco. Possibly not for many, many years, or possibly much sooner. Will we have learned in time how to predict and give warning so the city can be evacuated? Or will we even perhaps have learned how to prevent earthquakes? The race is on. The people of this delightful city prefer to put the threat out of mind. And yet, the threat is always present. Each year, scientists find new unexpected uses for satellites. How magnificent if this product of man's advanced technology could help show the way toward bringing an end to the age-old, sudden, striking terror of mankind. Till that bright day, satellites high above will keep watch on the earthquake below.