Watching the Earthquake Clock : ON SHAKY GROUND <i> by John J. Nance (William Morrow: $19.95; 432 pp.) </i> : THE COMING QUAKE Science and Trembling on the California Earthquake Frontier <i> by T. A. Heppenheimer (Times Books: $17.95; 266 pp.) </i>

A recent poll indicates that about two-thirds of the California population believes that there is a catastrophically damaging earthquake in our future. Regrettably, this majority does not necessarily base its belief upon a rational understanding of the seismic conditions that surround us. Witness the Nostradamus astrological flap of May, 1988.

The public appetite for pop-culture earthquake prognostications has always created a market for the purveyors of myths. And yet, the story of the unraveling during the last two decades of nature’s skein of seismic secrets is an absorbing saga that possesses sufficient drama and suspense to compete on its own terms with the most imaginative science fiction.

For the layman, access to the story of the acquisition of the new scientific understanding of earthquake vulnerability has been limited to the fragmented format of magazine and newspaper articles. But now, this deficit has been bountifully rectified by the virtually simultaneous release of two books that chronicle the evolution of seismic thinking during the last 20 years.

Although their subject matter is generally the same, the style and emphasis of “On Shaky Ground” and “The Coming Quake” contrast so much that both warrant the attention of those lay readers who are interested in understanding the impressive new development in this area of science.

Nance’s readers will recognize the style and format of his 1986 “Blind Trust” (William Morrow & Co.) in this new book. In “In Blind Trust,” Nance sought to portray the response of public policy to commercial airline accidents as an expensive way to learn safety lessons. In “On Shaky Ground,” he contrasts the emerging understanding of earthquake vulnerability with the public policies intended to cope with these circumstances.

Nance’s treatment in both books is set forth in a highly readable narrative documentary style, which relies heavily upon his interviews of the principals involved in the episodes that he recounts.

Because a major feature of the new scientific understanding is the fact that damaging earthquakes recur periodically along the same faults, Nance seeks to characterize the future seismic threat to certain communities through first-hand accounts of what has happened to them in the past. The book opens with a gripping narrative of the effects of the 1964 Alaska earthquake as it was witnessed by a score of interviewed survivors from communities along the coast.

Turning to science and continuing the anecdotal style, Nance presents the seminal observations made by the researchers of the effects of this earthquake and how the new data mandated changes in the existing conventional wisdom. The lay reader gets a glimpse of how science is done through the revision of earlier interpretations to conform to the constraints new data impose on our perceptions of reality.

Nance characterizes the further validation of the concepts of plate tectonics and periodic recurrence of damaging earthquakes with scientific anecdotes from sites in South America, Mexico and California. In this context, he goes on to present the current scientific expectations for future hazards at the sites of the great damaging earthquakes of the 19th Century at New Madrid, Missouri and Charleston, S.C. Nance also considers the even more challenging prognosis of future damage along coastal Oregon and Washington where geologic evidence suggests that great earthquakes have occurred in the prehistoric past.

Turning to policy, Nance profiles the recent disposition of Congress and state and local government officials in light of the new scientific insights and the policy lessons that could be learned from the past. His assessment runs the gambit from encouraging to disconcerting.

In “The Coming Quake,” Heppenheimer focuses upon the development of insights that have been derived from recently established methodologies for determining the recurrence periods of damaging earthquakes along specific portions of faults and the as-yet-unfulfilled efforts to predict imminent events in the short term (pinpointing the occurrence within hours to weeks).

Heppenheimer covers some of the same ground as Nance. He is acquainted with some and has interviewed most of the scientists he writes about, but in most places, his style is less anecdotal and more formal and his emphasis is more on the details of the science and less on public policy. The book also benefits from abundant maps.

Heppenheimer walks us through the principal earthquakes in California since Colonial times. He recounts the development of the Richter scale in the 1920s and summarizes the investigative approaches employed at the Seismology Laboratory at California Institute of Technology, where he once served as a research associate in aerospace engineering.

On the positive side of the research results ledger, Heppenheimer recounts the success of the dedicated individuals who have used geologic evidence of prehistoric earthquakes to decipher movement rates along the faults and the recurrence times between damaging events. He also summarizes the method of identifying seismic gaps along active faults, where strain has not been relieved since the last damaging earthquakes a sufficient number of years ago, to anticipate the future earthquake to be during the next few decades.

On the less successful side of the ledger, he documents the history of the literal and figurative rise and fall of the Palmdale bulge as a short-term precursor of the big one on the San Andreas Fault. He presents a fascinating discussion of the once highly touted dilatancy theory of the mid-’70s, which was professed to be a unifying understanding of the physical changes preceding earthquakes that seemed to confirm the usefulness of geophysical phenomena as short-term precursors.

He examines the genesis of the concept and the marshaling of the evidence that eventually discredited it. He also catalogues the relatively well-monitored events recorded in California since 1979, which have given little or no evidence of having been proceeded by short-term precursors.

In the face of the mixed expectations regarding the feasibility of predicting imminent events, Heppenheimer describes the very intensive studies in progress along the seismic gap at Parkfield on the San Andreas Fault. Here a magnitude 6 event has occurred approximately every 22 years since the last century, and the most recent event was recorded in 1966. This state-of-the-art effort is presently the most closely watched earthquake prediction experiment in North America.

Heppenheimer outlines the possible damage patterns that have been portrayed in emergency-response planning scenarios for portions of California. Finally, he summarizes several novel ways of reducing seismic hazard that may be feasible in the far future, including the controlled release of strain along faults such as the San Andreas by the injection of water into the fault zone.

Both authors succeed in bringing the work of dedicated scientists to life in these highly entertaining and informative books. The impression that the reader is left with is correct--science is beginning to learn how to define our broad vulnerability to earthquakes in time and space and more refinement of this important work is needed.

In the meantime, the feasibility of predicting imminent earthquakes remains an open question that can only be answered by continuing research.