What if the Big One Hit at Rush Hour? : SUPERQUAKE! The Last Days of Los Angeles <i> by David Ritchie (Crown Publishers: $18.95; 224 pp.) </i>

The earthquake that shook the Los Angeles area last October, killing three people and frightening millions, was the first to cause significant damage locally in 16 years, but in some respects, it was quite an ordinary event.

Each year, 11,000 temblors strike Southern California--one of the world’s most quake-prone regions. Because most of them are small, and unnoticed except by scientists who monitor earth movements, last October’s may have played an important role in awakening a new generation of Southern Californians to the hazards of living in an earthquake zone.

But while the October quake may have seemed like a big one, it was really quite moderate as earthquakes go. Scientists believe that a truly big quake has been building for years in the San Andreas Fault, 40 miles north of Los Angeles, and will probably strike sometime in the next half-century. When it does, they say it will release 1,000 times the energy of the recent quake and cause many times the destruction.

David Ritchie, a science writer who edits a newsletter on the Strategic Defense Initiative, has written a book that is welcome chiefly as a reminder that a big quake is on its way.

Ritchie is at his best describing the inexorable geological processes that explain why a major earthquake is expected here.

He is at his worst describing the consequences expected in Los Angeles, occasionally seeming to have trouble avoiding a temptation to sensationalize. “. . . Readers may ask,” he writes, “ ‘Will Los Angeles fall into the sea when the next superquake strikes?’ ”

Reassuringly, and with reason, he declares: “The answer is no.”

But on the very next page, he is not so sure. “. . . There is practically no chance,” he writes, “that Los Angeles will tumble into the ocean.”

In geologic time, Ritchie writes, land masses--indeed, whole continents--appear to be on the move, adrift probably because the Earth is swelling. North America, he says, is slowly headed west.

The movement, Ritchie writes, is traceable to the construction of the earth’s outer layer--a dozen or so 10- to 50-mile-thick plates that “float on the denser rock below . . . much as icebergs float on water.” Plates form when, for reasons that are not clear, “molten rock from the Earth’s interior rises to the surface, cools and solidifies.” They spread as more hot rock comes to the surface.

Eventually, plates bump, and where they do, mountain ranges are pushed up, and earthquakes frequently occur. In California, North America’s plate collides with a Pacific Ocean plate at the San Andreas Fault--a fault being a crack in the crust where “chunks of crust are moving, or have moved, relative to one another.”

At the San Andreas Fault, the Pacific and North American plates “tend to ‘stick together,” Ritchie says, “and build up tension, which gets released every century or so in the form of a major earthquake.”

Ritchie lists and briefly describes notable California quakes, and the sheer number of them--he goes on for 35 pages to recount 200 years’ worth--is in itself a convincing argument that an end to major earthquake activity here is wishful thinking.

He spends much time on the last big San Andreas quake--in San Francisco in 1906--and relies on contemporaneous accounts of literary figures to advantage. “San Francisco is gone!” Jack London wrote for Collier’s magazine. “Nothing remains of it but memories and a fringe of dwelling houses on its outskirts.”

Ritchie writes that 2,000 people were probably killed and 250,000--half San Francisco’s population--were left homeless. Many set up tents in parks and fought fires, he reports. “The fires were the greatest social levelers San Francisco had ever seen.” A desperate militia resorted to destroying whole blocks with artillery to create fire breaks. Crocker bank employees piled a million dollars in bonds into a wheelbarrow and marched it to a boat, which they sailed to a safe anchor in the middle of the harbor until the fire danger had passed.

The centerpiece of the book is a fictional chapter on the destruction of much of Los Angeles--a construct based on a truly worst case.

Ritchie, who is often ham-handed as a writer, begins with a rather lame paean to the the city, calling it a diverse “city of paradoxes . . . almost anything one can imagine, and its antithesis at the same time.”

Then he posits a scenario that he admits is unlikely.

Rather than the next big quake coming along the San Andreas, well to the north of the city, as most scientists expect, he has it occurring in the city’s heart, along the lesser-known Newport-Inglewood fault complex, which runs from the West Los Angeles suburbs to Long Beach. “ . . . nature confounds the scientists,” he says by way of explanation.

While most scientists believe that the Newport-Inglewood fault is capable of producing only a 7.5 quake on the logarithmic Richter scale, Ritchie for some reason has decided that is not bad enough--even though scientists believe that a 7.5 quake there would result in more casualties than an 8.3 on the San Andreas.

Declaring that the “magnitude is a surprise as well,” Ritchie makes his quake a 7.8. Then he picks the worst time for it--rush hour--and pushes casualty projections to their upper limits: 42,000 people killed and a million injured--125,000 of them serious enough to be hospitalized.

But while the reasons for his apparent exaggerations are a curiosity, quarreling with them is largely beside the point.

The portrait he paints of Los Angeles--skyscrapers still standing, many older buildings destroyed, widespread landslides, water and electricity widely unavailable, banks closed, streets blocked, dangerous chemicals released, some soils liquefying, and so on--is generally in line with what scientists expect.

It is certainly a portrait that is worth knowing about and, to the extent that it is possible, preparing for.

Ritchie, however, is not very interested in preparation. After scaring the wits out of the reader--albeit with reason--he devotes only a half of the book’s last page to suggesting ways to handle life during and immediately after an earthquake.

His most serious omission may be the desirability of stockpiling food and water. Most experts suggest storing enough to last 72 hours, when whole neighborhoods may be cut off because of blocked streets and individuals may be left to fend for themselves.

(Readers interested in obtaining more information on preparations may want to send for an American Red Cross booklet called “Safety and Survival in an Earthquake,” available free from Southern California Earthquake Preparedness Project, 600 S. Commonwealth Ave., Suite 1100, Los Angeles 90005.)

Much of Ritchie’s book, which also includes earthquake histories of the rest of the country in a chapter entitled “California Is Not Alone,” reads as though it were haphazardly slapped together. He uses clumsy transitions, often addressing the reader directly and stiltedly, as a college student might address a professor to guide him through the rough spots of a term paper. “Since an impending earthquake is the subject of this book,” Ritchie writes, “we should devote a chapter to the phenomenon of earthquakes. . . . “ “To understand just why quakes strike California so often,” he says, “let us look back in time to see how California formed . . . let us now look closely at the geology of Los Angeles and its environs. . . . Let us look next at just how those faults can spread destruction.”

Despite these shortcomings, Ritchie’s book contains some informative science writing. It is when it strays into science fiction that the book gets into trouble.