Solving the riddle of the shuddering earth (Fortune Classics, 1965)

March 27, 2011, 5:39 PM UTC

Editor’s Note: Every week, is publishing favorite stories from the Fortune magazine archives. In the February 1965 issue, Lawrence Lessing dug deep into research providing clues about the causes of earthquakes in this story, for which he won the AAAS Westinghouse Science Journalism Award. It was the height of the nuclear age — before Chernobyl or Three Mile Island — and it was just one year after the Alaskan coastline was hit by a magnitude 8.4-8.6 earthquake. As he explored the scientific mysteries of earthquakes, Lessing concluded: “It could even happen in New York.”

By Lawrence Lessing

Undersea exploration, nuclear testing, and observation of the orbits of space satellites-all are adding new clues to the causes of earthquakes. The new knowledge may provide ways to warn against these disasters and to minimize their damage.

The earthquake that struck Alaska’s southern coast on the evening of Good Friday, March 27, 1964, was of a magnitude to erase complacency about this horrendous phenomenon. It was the biggest ever recorded on this continent. On a seismic scale of magnitudes from one to ten, it registered 8.4 to 8.6. In actual energy released, it far outdid the great San Francisco quake of 1906. For one and a half to four minutes, as if under the blows of a mighty battering ram, the earth shook over a land area of nearly 500,000 square miles.

In places as distant as Illinois, New Jersey, and Florida, water-well levels precipitously dropped two to ten feet. In the main shock area, centered about seventy-five miles east of Anchorage, a 400-mile-long subterranean rock formation extending down the coastline and out to the southern tip of Kodiak Island was rent asunder. On one side of this enormous fracture, the land-including part of a mountain range dropped as much as eight to ten feet; on the other side, the coast-and one offshore island-rose as much as thirty to fifty feet. Later measurements showed that the fracture had permanently displaced the earth’s crust as far west as Hawaii.

In the main shock area, huge avalanches, landslides, crevasses, and mud spouts knocked out all utilities, roads, transportation, and communication. A giant, thirty-foot seismic sea wave or tsunami, generated by the main shock, and many shorter range but taller waves, generated by submarine landslides, dashed upon the coast, wiping out Alaska’s fishing and canning industry, and spreading havoc as far south as California. Small coastal towns, such as Chenega and· Valdez, all but disappeared; Seward lost its entire waterfront; and Anchorage sustained the greatest amount of total damage to schools, offices, and homes. There two small boys playing in their yard suddenly disappeared down a yawning crevasse. In one night of primordial terror some 115 lives were lost and over $350 million in damage was sustained.

For centuries men have accepted these catastrophes fatalistically. Indeed, the human race has a heroic capacity for picking itself up and forgetting such disasters almost before the last tremors fade. But evidence is growing that the Alaskan quake marks a real turning point. While the reverberations from aftershocks still continue and rebuilding goes on apace, a long-range scientific effort is at last getting under way to solve the riddle of what causes earthquakes. The hope is that this study will make it possible to develop a warning system against big quakes, whose surprise factor is the worst menace to human life, and to prescribe protective measures against their most damaging effects.

The Alaska quake was the most observed earthquake in history. By Easter Sunday of that tragic weekend the U.S. Coast and Godetic Survey had flown in five special portable seismographs from its laboratory at Albuquerque, New Mexico, to get a full record of aftershocks. It also installed fifteen strong-motion seismographs, the first in Alaska, to study the vibrations of buildings under shock; this would aid in repairs and in future building design. Finally, Coast and Geodetic swiftly began sea and aerial surveys to remap the deranged harbors, coastline, and terrain. Japan, an old hand at earthquakes, flew in experts and equipment to help round up data. The U.S. Geological Survey rushed in teams to assess substrata changes, rezone areas for reconstruction, and begin compiling a complete record of the quake’s geologic and hydrologic effects.

Coordinating all this activity is the President’s science advisory office, aided by a big committee of the National Academy of Sciences. A special panel of experts appointed by Donald F. Hornig, the President’s chief science adviser, is realistically weighing the prospects of finding a method to predict big earthquakes. Recommendations for a broad national and international program are expected early this year.

It could happen even in New York

The effort is long overdue, for earthquakes are by no means uncommon occurrences in the U.S. Forty-eight major convulsions have been registered so far in this century in Alaska and the Aleutian Island arc, the nation’s most active earthquake area. A close second, with fewer big quakes but many smaller ones, is the West Coast region. But these are by no means the only danger zones. The Utah-Montana-Wyoming triangle has been active recently. A century and a half ago three big quakes in quick succession struck New Madrid, Missouri; and in 1886 Charleston, South Carolina, was devastated. The mid Mississippi Valley, the southern coast, the St. Lawrence River Valley, and even the New England area around Boston are all seismic regions that have been active in the past. The fact that an area has been quiet for a long time is no reason to believe that it will not be struck tomorrow, with catastrophic results even to such a seemingly impervious city as New York. In the last fifty years alone the U.S. has sustained at least $1 billion in earthquake damage, and the cost is bound to rise as urban areas spread and grow more complex. The Alaskan earthquake simply precipitated a rising belief that the time has come to do something about the problem.

Only a few years ago any suggestion that earthquakes could be predicted would have drawn snorts of “quackery” from the profession, for the gaps and uncertainties in knowledge were so great that forecasting was out of the question. The uncertainties are still very big. But hopes have been raised by the great advance and confluence of the earth sciences, from geology and geophysics to oceanography, armed with important new information from nuclear-bomb testing and space. The basic earth sciences have been in vigorous upheaval for a decade or more, and this ferment augurs well for finding a solution, because the problem of earthquakes reaches down deep into the origin, structure, and dynamic behavior of the earth itself.

Interestingly enough, most of what knowledge there is of the interior of the earth comes from the seismographic study of earthquakes. Other instruments measuring the earth’s gravity, magnetic field, and heat flow have contributed much valuable supporting data and in the future may add even more. But the most useful of all tools is the seismograph, invented only late in the last century by the Englishman John Milne, while he was sojourning in quake-ridden Japan. The seismograph is essentially a pendulum or delicately balanced weight, suspended in a rigid frame on bedrock, which transmits and records electrically the relative wave motions of the earth under shock. Long, intricate analysis of these seismic waves, their directions, velocities, travel times, refractions, and reflections through the layers of the earth, enabled seismologists to build up a gross picture of the earth’s interior.

With a fire in its belly

This is the now famous three-layered model of the earth: a very thin crust, covering an enormously thick, solid mantle, enwrapping a molten, liquid core. Subsequent refinements of technique have identified seven distinct layers or shells within the earth, but these are essentially divisions of the major three. Below the crust, only a few miles deep, stretches the mantle, some 1,800 miles thick to the boundary of the core. The precise upper limits of the mantle were discovered in 1909 by the Croatian seismologist, Andrija Mohorovicic, who noted that seismic waves suddenly jumped in velocity only a few miles below the surface of the earth, indicating a sharp change in the nature of the materials. This transition region is the now famous Mohorovicic discontinuity or Moho. By comparing the velocity rate of shock waves through the mantle with the rate through known materials in the laboratory, seismologists were able to infer that the mantle is composed of something resembling a dark, dense basaltic rock known as olivine.

Below the mantle, some 2,160 miles down to the center of the earth, is the core, generally believed to be of a heavy iron-nickel composition, though recent opinion is veering toward the idea that it is simply a continuation of the mantel material in a different state of matter at these greater depths. Early seismologists inferred that the whole core was liquid because they discovered that a certain component of seismic waves called shear waves, which cannot pass through liquids, did not pass through the core. But it is now believed that the inner core is solid, and only the outer core a molten liquid. That at least part of the core is molten is inferred from the probable temperature-pressure level at these depths. Readings in deep mines and boreholes show that the internal heat of the earth rises sharply with depth, reaching an estimated 2,500° Fahrenheit only fifty miles down. Only the increasing weight and pressure of matter, which raise the melting point of materials, keeps the mantle from being molten. In the core the heat outstrips the pressures, causing the material to melt. The tremendous heat entrapped in the core is generally thought to have come from the compressive forces exerted in the early formation of the earth and from radioactivity in its substance, originally about fifteen times more intense than it is now. Thus the core is still glowing at a temperature estimated at somewhere between 3,600° and 18,000° Fahrenheit, under pressures of nearly 45 million pounds per square inch.

The earth, therefore, is a dynamic structure that has evolved over many millions of years-just over four and a half billion years, according to the precise time clock of radioactive elements in its substance-and it is evolving still, with a fire in its belly. Geologists have read the history of its constant change in rocks and rills. Mountains rise, are ground down, and continue to rise elsewhere. Continents emerge in places where once, there were seas.

But the most spectacular and abrupt of all changes occur when the earth shakes. For geophysicists it is not enough to know that an earthquake occurs when a fracture or fault in the earth’s crust gives way through internal strain or some deep collapse below, causing a ‘shear movement or subsidence in the crust. These are just local effects. Earthquakes are intimately related to such larger, slower movements as the formation of continents and the building of mountains, and to the deep forces within the earth that cause these changes. Before they can begin to explain and eventually to predict earthquakes, geophysicists need to know the general pattern of those forces.

New cracks in the earth’s armor

In the last decade or so, advances in: instruments and techniques have enabled seismologists and other explorers to throw a few shafts of light into some of these deep places. Much of the advance has been in the sheer organization of instruments on a scale new to geophysics. In the International Geophysical Year, 1957-58, leading nations collaborated on a vast physical audit of the earth, As part of this, Columbia University’s Lamont Geological Observatory installed the first skeleton network of standard seismographic instruments ever to operate on a global basis. Following up on the IGY work, the international Upper Mantle Project set the U.S., Canada, West Europe, and Russia to building up standard networks of their own and drilling a series of deep boreholes, the most ambitious of which is the U.S. Project Mohole (see FORTUNE, May, 1963). Its object is to drill down to the Mohorovicic discontinuity through the ocean floor and to bring back a sample of the mantle itself, which has never been conclusively examined before. Finally, to handle the vast amount of data flowing in, the ubiquitous computer has been integrated into the whole system to speed up and extend analysis a hundredfold, even to the point of directly controlling, recording, and analyzing seismograms.

Meanwhile, the instruments themselves were undergoing great extension and refinement. Leading the advance was a new class of long-period seismographs, conceived mainly by Hugo Benioff of California Institute of Technology. These are able to detect and sort out long earthquake waves undulating around the world through the surface of the crust and upper mantle, thus giving scientists a clearer picture of this region. They also are able to sort out, for the first time, the free oscillations of the earth, its natural vibrations under rotation.

From seismography in oil exploration, where explosive charges are used to simulate seismic events, came sophisticated, portable electronic instruments. And’ along with them came methods of arraying instruments over the earth to refine reception, and methods of sounding the ocean bottom and sedimentary layers, pioneered by Lamont Observatory’s noted director, Maurice Ewing.

From Project Vela, the Defense Department’s big effort to develop reliable means of detecting underground nuclear explosions, came still further refinements. Indeed, techniques have been so improved that seismologists are now able to locate and discriminate between small earthquakes and underground explosions to an extent unheard of a few years ago, bringing within reach an inspection system capable of operating entirely outside an antagonistic country. And this focus on “small events” turned seismologists’ attention to the study of small earthquakes, heretofore largely ignored.

Out of all this came some notable discoveries. The analysis of long surface waves, for instance, showed that the crustal layers below the oceans differ considerably in depth, density, and composition from those below the continents. Underlying the oceans is a heavy, basaltic type of rock only three to four miles deep; under the continents is a lighter rock, mainly granite, some twenty to twenty-five miles thick, with the roots of mountains extending even deeper than that into the mantle, like partly submerged icebergs in the sea. This means that the Mohorovicic discontinuity, instead of being a symmetrical boundary under the crust, rises close to the surface under oceans and dips down deep under continents, setting up pressures and strains on the rims of continental blocks-precisely where most of the great earthquakes occur. At the same time, long-wave studies have also confirmed the suspected existence of a “soft” layer in the upper mantle, some 35 to 155 miles down. Wave velocities drop in this area, indicating that the rock is in a plastic state or even molten in places, owing to some temperature-pressure imbalance. These additional irregularities may further account for earthquakes as well as for volcanoes.

Deeper than the Grand Canyon

Perhaps the most provocative geophysical discovery of the decade is a mighty interconnected chain of submerged mountain ridges and valleys (see map, pages 166 and 167), now known to stretch for some 40,000 miles under the oceans of the world. Hints and fragments of this globe girdling chain were glimpsed for nearly a century. But its full dimensions were not grasped until the late Fifties, when the Lamont Observatory research ship Vema and other IGY voyagers seismically sounded its main branches through the mid-Atlantic, Indian, southern and mid-Pacific oceans, and on up the great East Pacific Rise, curling along the American West Coast to Alaska.

These underwater mountains are quite unlike those found in the upper world. They rise in great, sharp, rugged scarps of basalt, some nearly as tall as the Himalayas. Down their centers run deep, long valleys or rifts, many deeper than the Grand Canyon, extending for hundreds of miles. Heat flowing up from the rifts registers higher than almost anyw4ere else on earth. Along their length, relatively small, shallow earthquakes and volcanic activity occur in profusion. From their bottoms, oceanographers have dredged up basalt boulders, indicating a continual upwelling of soft or molten matter, perhaps from the mantle itself. This causes the rising scarps and rifts to spread apart at a small, measurable rate. Analysis of the boulders shows they crystallized out of molten matter no more than ten million years ago, indicating that the rifts are a comparatively young feature of the earth. All together, the rifts form a huge tension crack in the earth’s crust, running in an almost continuous line nearly twice around the earth.

In a few places in the world the rifts actually emerge on dry land, where they can be observed as steadily widening fissures or crevasses, which until recently defied explanation. One of these strange formations, the famed “rift valleys” of East Africa, is now seen to be a landward extension of an Indian Ocean ridge. Another, a northerly continuation of the Mid-Atlantic Ridge, runs jaggedly across a great central graben or depression in Iceland. Measurements over the years show that this crevasse is steadily widening at a rate of a fraction of an inch a year and pushing up matter to build up the ridges on both sides.

Is the earth expanding or contracting?

All these discoveries raise fundamental questions about the evolution and behavior of the earth. To begin with, a comprehensive theory is needed that will account not only for the familiar continents, ocean basins, mountains, and earthquakes, but for all the new phenomena as well. In an effort to find an all-embracing explanation, theories old and new have been brought to a boil.

Perhaps the oldest theory is that the earth has been contracting ever since it began cooling down from its early molten state. As speculation goes, this shrinking caused the hardened crust to shrivel like the skin of a dried prune as it adjusted to new dimensions, thus raising continents and mountains and causing earthquakes.

Old-school geologists still cling to this theory, but it has been badly weakened in recent years. For one thing, the theory assumes that the earth was formed, as was once widely believed, out of a molten blob torn from the sun. But modern cosmologists find strong evidence that the earth, like other planets, was formed by the cold accretion of dust and gases whirling in a primordial disk around the sun. Only gradually, over a period of about a billion years, did it heat up to the molten state through compression and radioactivity. The amount of contraction that could have occurred in cooling off since then is not sufficient to account for the earth’s mountain heights and ocean depths. Moreover, it is highly doubtful whether the interior of the earth has yet lost much of its original heat, because its huge mass is a slow conductor and radioactivity is constantly adding heat.

A newer theory is that the earth is actually expanding. This was first suggested about a quarter of a century ago, on purely cosmic grounds, by the great British theoretical physicist, P.A.M. Dirac.  He reasoned that in an expanding universe, in which all bodies are seen to be rushing away from one another at a measurable rate, the force of gravity in any given body must be gradually diminishing with age. Even a slight decrease in the earth’s gravity, unmeasurable as yet by any ordinary means, could cause its matter to expand by as much as 1,100 miles in circumference in 3.25 billion years. The expansion theory, long dormant, suddenly gained support from the discovery of the mid-ocean ridges and rifts. For this global system covers a surface area about equal to that of the calculated expansion, and the rifts might well be the expansion joints where matter from the swelling interior of the earth is oozing out to form new crust.

A third major theory of the earth, which may or may not include expansion, is the theory of continental drift. First conceived about fifty years ago, mainly by a German geologist named Alfred Wegener, it has acquired many adherents as a result of recent discoveries.  Noting the curious jigsaw fit of continental profiles, particularly between the Americas and Europe-Africa, and the curious similarity of fossil remains in widely separated continents, Wegener suggested that once there was only one mammoth continent that later was split up. Since then the continents have been slowly drifting apart, floating like great, buoyant, granitic rafts on the heavy, sluggish basalt beneath.

The drifting continents

For years this idea was largely dismissed as fantasy, since there was no evidence anywhere in the seemingly solid mantle of any heat currents or other flow mechanisms to give the continents such mobility. But lately new information has been piling up to support the idea of drift. One bit of evidence comes from an exotic branch of geophysics known as paleomagnetism-the study of magnetic lines of force in ancient rocks. It was discovered that the lines of force frozen into continental rocks at the time of their crystallization are all askew with reference to the present, position of· the north and south poles. Continents must once have been oriented to the poles very differently. And the recent discovery of a “soft” layer in the upper mantle supplied a plausible medium upon which the continents might be drifting.

But the strongest evidence was again provided by the discovery of the mid-ocean system of ridges and rifts, which fitted into the theory of continental drift in either of two ways. If the earth is expanding, as the mid-ocean rifts seemed to indicate, then this expansion is what caused the original splitting up of the continents and their apparent drifting apart, like patterns on the surface of an expanding balloon. On the other hand, if the earth is not expanding, as some still maintain, then the rifts could support the theory of drift in another way. They could well be the vents through which huge, internal heat currents or convection cells-circular, rolling currents like those seen in boiling liquids-reached the earth’s surface, pushing up mantle material, forcing a plastic flow of light materials to the underside of continents, causing the continents to drift, and compressing them horizontally to form the wrinkled folds of mountains and set off earthquakes.

What precise mechanism could thus cause the heavy, enormously thick, and solid materials of the earth to flow? Egon Orowan, a solid-state physicist at M.I.T., has recently investigated the matter, using polycrystalline alumina to simulate the materials in the upper mantle and crust. He concludes that convection heat currents in the crystalline mantle could induce a type of slow plastic movement known as hot creep-a sliding of crystals on one another-which, as strains accumulate in the rock structure, could cause creep fractures, wrinkling, and earthquakes.  By various calculations he concludes that the U.S. and the whole western Atlantic are creeping or drifting westward into the Pacific at a rate of about one centimeter per year.

There are still many objections to these upsetting new theories.  The drift hypothesis, for instance, would require that a huge section of the earth’s crust between rift valleys be moving inexorably in one direction, tending to open the rift on one side of a continent and to close the rift on another side. Actually, however, the rifts appear to be opening on all sides of every continent. And, the expansion theory has been challenged by two U.S. Geological Survey physicists, who performed a modern version of the amazingly accurate measurement of the radius of the earth made by Eratosthenes about 260 ‘B.C., and found that the radius has not varied by more than a few miles in the last 200 million years.

Meanwhile, a fourth theory has come to the fore. It holds that the earth is neither expanding nor contracting but is essentially stable and solid all the way down to its core. This theory centers around the teachings of Britain’s great old master geophysicist, Sir Harold Jeffreys, who maintains that the earth is much too solid, rigid, and strong to allow such mass movements in its crust and convection currents in its mantle as continental drift would imply. In this view, continents were formed in the molten stage by upward segregation of lighter materials, like slag rising to the top of a molten ingot of steel, and they remain frozen and embedded in the now solid mantle. Indeed, according to a famous computation by Lord Kelvin, the mantle has about double the rigidity of steel. Hence, except for some local fluidities, the earth is not plastic but essentially elastic, like steel.

This concept of the earth was startlingly confirmed in 1960 from a totally unexpected quarter-space. Observations of the irregular orbits of space satellites, which reflected a highly variable gravitational pull from the earth over large areas, led to two important though still controversial discoveries. One was that the earth is slightly pear-shaI1 d, bulging more below the equator than above. Small as this f’ regularity is, it causes the earth to depart so far from being a perfect oblate spheroid that it apparently exceeds the calculated strength of its own materials. The second discovery was that there are extensive irregularities in gravity over the earth, like great shallow hills and bowls. Eight major gravity anomalies have been located, the two greatest being a deep depression or “bowl” off the tip of India and a great “hill” or rise in the New Guinea area. The gravity “hills,” being areas of great strain in the earth’s mass, appear to coincide with the greatest earthquake zones.

To sustain such gross irregularities in shape and mass without breaking apart, the earth must be exceedingly rigid and strong.  The strains generated by these anomalies, according to space geodesists, must go down to the very core of the earth. They are so great that, to account for them, some have refurbished the theory, first suggested by George Darwin, that a great catastrophe once tore a huge mass out of what ·is now the Pacific Ocean to form the moon and perhaps Mars. A more plausible hypothesis, suggested by Gordon J. F. MacDonald of the University of California at Los Angeles, is that the deep strains are caused by a ten-million-year lag in the adjustment of the earth’s shape to its declining rate of rotation. This lag stores vast tension or energy in the earth, like a coiled spring, accounting for all the shifts in its crust, including earthquakes.

In this clash of theories, science progresses. And when the din is at its highest, the greatest advances may be expected, often through a melding of conflicting viewpoints. For instance, Walter M. Elsasser of Princeton University now suggests that all changes or movements in the earth of any significance are confined to a thin surface layer only 200 to 250 miles deep, which would leave the bulk of the earth relatively stable, strong, and solid, while allowing some form of drift or mobility in the upper layer. In any event, most geophysicists believe that it will be only a matter of a few years before many of the key issues are decided.

Closing in on earthquakes

While this broad inquiry into fundamentals goes forward, without which earthquakes would never be fully understood, geophysicists are also bent upon a closer, more practical study of individual earthquakes themselves. Much remains to be learned about the character and pattern of their activity, with an eye to prediction. Volcanologists have reached a good rate of success in predicting eruptions by studying specific volcanoes over long periods. And for a decade the U.S. Coast and Geodetic Survey has operated a tsunami warning system out of Honolulu; by checking special tide gauges dotted around the mid-Pacific, it is able to predict the arrival time on shorelines of the giant, 500- mile-per-hour sea waves generated by oceanic earthquakes. Coast and Geodetic is now extending the system to Alaska, and is also seeking a way to predict by computer analysis not only arrival times but also wave heights. The earthquake problem is much more difficult, but it too may yield to an organized effort.

A number of hopeful lines of research open out. One is the study of the foreshocks and aftershocks of big earthquakes to see whether they reveal a warning pattern. For years the Japanese and others have tried this without much success, but a few broad hints have emerged. For one, the Japanese found that big quakes generally followed a counterclockwise course around the rim of the Pacific. More recently, accurate location of earthquakes in depth has revealed a fairly regular pattern of quakes moving up and down major faults. Today, more comprehensive computer analysis of small earthquakes is available from a worldwide network of 125 seismographic stations operated by U.S. Coast and Geodetic, and the hope is that more significant patterns will emerge.

A still more promising line of research, untried on any big scale as yet, is the burying of strain, tilt, and displacement gauges broadside over a major earthquake area. Observations of the buildup of strain or tilt in underlying rock formations may reveal a warning pattern as strain reaches the breaking point and an earthquake occurs. Dr. Frank Press, chairman of the special national advisory panel on earthquake prediction and director of California Institute of Technology’s Seismological Laboratory, has a $250,000 grant from the National Science Foundation to try such an instrumented experiment in the great San Andreas Fault area around San Francisco. The San Andreas Fault is a huge, steadily moving fracture slanting down the state from a point 130 miles north of San Francisco nearly to the Mexican border. Measurements show that one side of the fault is moving in relation to the other at a rate of about two inches a year. When the strain reaches a critical point, another big quake will occur. The area may be almost due for one.

Other clues are worth pursuing. An oil-prospecting magnetometer registered a curious shift in field just prior to Alaska’s Good Friday quake, hinting that magnetic fields may have some relation to earthquakes. Something might be learned from the study of microseisms or tiny earth tremors, which are little understood though they show up in all seismograms. The great difficulty in such lines of investigation is to distinguish anything significant against the background of constant minor shiverings or rumblings in the earth, including the hundreds of major to minor earthquakes occurring somewhere in the world every day. Obviously it will take long and patient observation to begin to see a pattern upon which to base predictions.

Building to withstand them

Pending the discovery of a method of forecasting earthquakes, however, many practical measures can be taken to lessen the damage from them. The first is the careful zoning of active earthquake areas, based on geological foundation studies, and the enforcement of codes prescribing what may be built and where. One of the most damaged districts in Anchorage was a new residential area, where landslides and shearing action turned most of the homes into matchwood. Only five years before a U.S. Geological Survey report warned that the soil in that region was unreliable. Most of Alaska’s towns are built on ‘similarly unconsolidated silty or clayey coastal soils, dangerously subject to slides. Only strong shoring, drainage, and soil conditioning can reduce the risks on such shaky ground.

Similar dangerous ground conditions exist elsewhere, around Boston, in the Puget Sound area, and all up and down the California coast. One smart residential district just below San Francisco’s Telegraph Hill has been built on filled and that is liable to slide away in any major quake, and other developments are mushrooming on shoreline landfills,’ bulldozed hillsides, and other questionable areas, posing a danger for the future. Real-estate developers have resisted clear earthquake zoning so strenuously in the past that to date no detailed U.S. zoning map is available.

Much also remains to be done about the building of earthquake-proof structures, beyond providing the lateral bracing and reinforced walls prescribed in most quake areas. Even in California, where the strictest building code has been in effect only since 1933, the law has grown lax and inadequate under the pressures of burgeoning population and real-estate development. Last year, however, Los Angeles passed a new city ordinance requiring all major new buildings to install strong-motion seismographs, patterned on a new U.S. Coast and Geodetic instrument, to study the motion of the buildings under tremors and to gather data for improving future design. Through such studies, and the mounting effort to understand and predict earthquakes, this old earthly affliction may yet lose some of its horrors.

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