constant threat the remote but real possibility of a great disaster like all great cities it has drawn together men and women from many places many backgrounds seven hundred thousand people live here during the working day that number is twelve with  and yet a specter walked the streets shoulder to shoulder with the people for san francisco lives nearby one of the most severe  follow the satellite radios back bast quantities of data that enrich our understanding of subjects from pollution to mining from fishing to farm the flood control put it as well bring a better understanding the birth place that was a subject for which the spacecraft held little promise a time would tell a different story the satellite looks now not an earth that is constantly changing pressure continues until at last the rock splits apart usually along an already weakened area called the fault line one periodic lay the people of california get a gruesome reminder of what can happen when the earth suddenly moved to san francisco nineteen zero six five seventeen a and actually see down here on my head is the actual four point plan that extends many miles down of the earth where the earthquake actually started and what causes earthquakes this green script represent from valley cards along the san andreas fault  three black scrips represent prefab so that were built across the fault many years ago fences which gradually become the former or better because of the horizontal move out 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 spreads and break apart this is an earthquake the rocks crack under the enormous stress until one section of the ocean floor springs suddenly up the water above it is thrust up the same way this vertical wave erupts to the surface and begins speed up to five hundred 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 ten story building is the dreaded tsunami or tidal wave earthquake that 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 shocker one bracket the bay area of san francisco in addition to the major faults there is a whole slew of lesser ones and entire system up anyone could be the 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 one nine hundred seventy one the san fernando valley outside los angeles we desperately need to know more about earthquakes to discover the secret of predicting them in time to get one nasa is working to support an earthquake research being done by the u s geological  of here if we look at that on the earth damage we can extend that's about sixty miles more exciting is one down here on the earth two major very major structure cuts across the whole mountain range they've never known about before and till they have their entire fault systems revealed for the first time by satellite knowledge like this may one day help to save many thousands of lines satellites are playing another even more important role in earthquake research in this nasa project or developing a prediction capability to stations like this have been erected five hundred miles apart on opposite sides of the sand and ray assault 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 quasars stars outside our galaxy to detect these minute earth moves scientists hope that applying space technology to this earthly problem may one day and they build them to say here the stress has reached its limit here about suction zuck today an earthquake will occur but today no one can say when an earthquake might rumbled san francisco possibly not for many many years or possibly much sooner well we have learned in time how to predict and give warnings so the city can be evacuated or when we even perhaps have learned how to prevent the earthquakes the race is on the people of this the light bulbs that they prefer to put the threat out of mind and yet the threat is always 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 o