Many of us breathed a little easier after October 17, 1989. The Lorna Prieta earthquake, 7.1 on the Richter scale, meant that the big one, talked about for decades, had finally happened. And, bad as it was, we had survived.

There are two things wrong with that. First, Lorna Prieta was not the big one. It was a moderately big one, certainly destructive to some parts of the Bay Area, but nowhere near the size of the great San Francisco earthquake of 1906. Second, having an earthquake like Lorna Prieta has little to do with the likelihood of having another one on a different fault, somewhere else in the area.

The inevitability of a damaging earthquake still confronts everybody in the Bay Area, and we still risk substantial damage. A new study, released in July 1990 by the United States Geological Survey, says that there is a 67 percent chance of another earthquake the size of Lorna Prieta during the next 30 years and that the quake could strike at any time, including today. In other words, scientists think that a magnitude 7 or larger earthquake is now twice as likely to happen as not to happen. This is a substantial increase, since in 1988, scientists thought the chance for such an earthquake was 50 percent Gust as likely to occur as not to occur) within 30 years.

The new report also says that the next one will most likely strike farther north than Lorna Prieta, somewhere between San Jose and Santa Rosa on either side of the Bay. The epicenter of the October 1989 quake was in a sparsely populated area. The next one, according to the study, will likely be centered in a more populated area. During the Lorna Prieta earthquake, shaking was so severe in the Santa Cruz Mountains that a van overturned, treetops snapped off, and many people were thrown to the ground. Because the next one is expected to strike closer to an urban area, it will cause much more damage.

Fortunately, there is something we can do about it. By taking actions, such as those described in this booklet, we can drastically reduce the losses and we can make the Bay Area a safer place to live. Earthquake damage is particularly great in certain locations and in certain buildings. Most locations and most modem buildings are relatively safe. By identifying the greatest hazards, we can set priorities for using our limited resources most effectively to reduce them. The choice is ours.