As Professor Otto Nuttli would come to find out 150 years later, the New Madrid sequence was the largest seismic energy release ever known or suspected on the North American continent, and it had managed to do major damage to sturdy one-story frontier buildings in a sparsely populated wilderness. By 1964 that “wilderness” had become the center of a great nation, with major cities radiating in all directions on land that in 1811 and 1812 quaked and gyrated with a force great enough to destroy a nonseismically engineered structure at distances of many hundreds of miles.
What if it occurred again? Is there any reason to believe that it can’t? Is there any assurance that it won’t?
Such questions had begun to haunt men like Nuttli, who had begun to research the immense intensity of the great New Madrid quakes and who realized the extreme vulnerability of cities like St. Louis and Chicago, Louisville, Cincinnati, Detroit, Dallas, Little Rock, Kansas City, and many others.
And then, of course, there is the matter of the high mudbanks on the eastern side of the Mississippi some 110 miles south of New Madrid. Several thousand acres of grassy plains covered the area in 1811 on a bluff overlooking the river, the grass roots growing in humus above a type of alluvial Jell-O of sedimentary outwash piled up over sixty feet of windblown loess seated over thousands of feet of other sedimentary rocks into the depths of the Mississippi Embayment—a water-saturated, unconsolidated aggregate of sand and clay and pebbles which vibrated, heaved, shook, split, lurched, jerked, and twisted with sickening motion during all three of the New Madrid main shocks, throwing down trees, rippling the ground with fissures, the sympathetic vibrations of the poorly consolidated muds increasing the effect of the seismic waves, rendering it unsuitable for anything not built to withstand a tremendous lateral beating of ground motion.
Even as a park it would be dangerous in an earthquake the size of any one of the New Madrid events. Yet on that very spot 150 years later would sit the brick and masonry buildings and homes, the nonseismically engineered roads and bridges, of one of America’s major cities: Memphis, Tennessee, its inhabitants largely ignorant of the degree to which their city sits squarely in the cross hairs of a seismic gunsight.
Chapter 11
Isla Guamblin, Chile—1968
The differently shaded bands along the sea cliff told the story. George Plafker sat back for a second, contemplating the obvious lines of demarcation—the layers visible beneath the lip of the cliff on the other side of the small bay—and thinking about their significance.
Hatless under a bright Chilean sun, he had to squint a bit to look at the whitish upper band running along the top half of the fifty-foot bluff. That one was merely a marker. It was the band beneath that was important, the one that held a vital record etched graphically in the rocky face of the Tertiary sandstone.
It was a gray layer 18.7 feet thick which had been underwater part of each day for hundreds of years. The layer ran completely around the bay, wherever the cliff was showing, clearly marking the area that during each tidal cycle had been washed by the waters of the southeastern Pacific, depositing small marine animals (such as barnacles) and supporting the algae and other plant life that had lived there.
Until the evening of May 22, 1960, that is, when it suddenly became dry land.
A day and a half before on May 21 something had snapped beneath the South American continental shelf a thousand kilometers to the north, triggering a large earthquake that reached a magnitude of ML 7.5, a serious upheaval that left destroyed houses and shaken Chileans in its wake.
The nightmare for southern Chile, however, had just started. Some thirty-three hours later, at 7:11 P.M. on the night of the twenty-second, a second quake began with another subterranean failure in an ancient snag between rock faces, and this time a ruinous torrent of seismic waves erupted in all directions, surpassing a magnitude of ML 8.5, releasing energy in greater amounts than the planetary convulsion which would rip through Alaska four years later in 1964.1
Suddenly the entire Chilean coast was in sickening motion, the seismic cataclysm tearing through the seashore and countryside, killing thousands, pulverizing masonry buildings, creating a devastating tsunami that headed out across the Pacific to kill more people in Hawaii and Japan, and rearranging the altitude of the seashore for more than a thousand kilometers north and south.
In a matter of seconds the island Plafker was sitting on had been thrust upward a total of 18.7 feet. At the same time, hundreds of square miles of land to the east up and down the coast had dropped as much as 6.5 feet, plunging some farmlands underwater and rearranging seashores and port facilities, docks and fishing beds throughout the country. The gray band George Plafker was contemplating—the intertidal zone of wet vegetation and marine organisms—had suddenly become high and dry even at high tide, and within days the organisms and vegetation were dying, left to bake in the sun during the following eight years until Plafker and his team members arrived by boat to find their remains and write their epitaph. It was a startling document, showing with precision exactly how much uplift the quake had caused at this exact location—and the technique of reading that visual record was the same one George Plafker had developed to a science in Alaska during the summer of 1964.
Now, in January 1968 during the Chilean summer, the thing that kept getting to Plafker was the similarity of the surface changes in Chile to those in the Alaska quake. Amazingly, the Chilean quake of 1960 and the Alaska quake of 1964 were dead ringers in many respects.
Of course, it was also amazing that the scientists who originally visited Chile right after the 1960 quake had missed so much. They never fully documented the vast areas of raised land and seafloor (emergence) or the incredible expanse of dropped real estate (subsidence). They had arrived with a preconceived idea, convinced that they understood the Pacific basin and the “accepted” model, which dictated that only steep vertical faults ring the coastal continental boundaries. They expected that an examination of the seismic wave records trapped from around the planet by the new World-Wide Standard Seismograph Network would show evidence of a buried steep vertical fault running roughly north-south along the Chilean coast.2 For some reason (which they made little effort to explain) their postulated fault had stored energy and released it in the form of a great quake. It was a neatly conceived theory, and it was also dead wrong.
Another team of eminent seismologists had reached the same conclusion about the Good Friday quake four years later in Alaska, bypassing the implications of Plafker’s 1964 work and his exhaustive documentation of raised and lowered Alaskan real estate. They concluded that just as in Chile, the cause of the great quake was a steep vertical fault (this one presumably situated along the southern Alaskan coast).
Both they and Plafker had read the very same seismograms, but had arrived at two entirely different conclusions.
“You see,” Plafker had explained to more than one friend outside geology, “you can interpret the seismographic data to mean either a steep vertical fault, or a shallow, subhorizontal dip-slip fault. That’s a radical difference, but the math will support either conclusion. If it’s steep and vertical, then there’s no indication of the seafloor moving or thrusting beneath the continental landmass of Alaska. It’s just a fault, a crack in the crust, that for some reason moved. But, if you read the same data the other way, you get a ninety-degree change in the indicated ‘plane’ of the fault that caused the quake. In that case it could only be a shallow dip-slip fault plane, which would mean that one layer has to be pushing under the other layer, alternately sticking and slipping—each slippage resulting in large earthquakes.”3
Plafker had not been aware of the impending conflict as he sloshed through the tidal areas of south-central Alaska during the entire summer of 1964. But as a geologist, he had been aware that there was no substitute for field observation. Foot by foot, beach by beach, Plafker and his associates in the USGS had documented the effects on the Alaskan seashore, gaining a reputation for near eccentricity by carrying
around pocketfuls of barnacles to see how long they could live out of water (and thus figure out how reliable an indicator dead barnacles could be on seaside cliffs, and whether they could indicate when and how far the seashore had been raised). The exhaustive studies documented a staggering expanse of raised and lowered landscape, which helped answer questions ranging from the cause of tsunamis to the amount of energy released by the 1964 quake.
The record was fascinating, but while George Plafker was working hard on observational field geology, he was also unwittingly establishing the inestimable value of a rather radical new form of seismic research that would shortly take seismology out of basement laboratories, bringing seismologists into the sunlight of geological fieldwork, and geologists like Plafker into the field of seismological research. It was a terribly simple concept of looking for records of seismic occurrences in geologic features, but it would take a decade to gain legitimacy, and twenty years formally to take on its proper title: Paleoseismology.
When George Plafker returned to Menlo Park from Alaska in the fall of 1964 and put it all together with the seismological evidence, the conclusion on the cause of the 1964 upheaval had seemed compelling: It had to be dip-slip. It had to be one massive section or layer of rock sliding beneath another. In this case that meant the Pacific floor was sliding beneath the Alaskan landmass, which was part of the North American plate. There was no way the quake could have been caused by a vertical fault running hundreds of miles along the Alaskan coast and cutting more than a hundred miles into the crust and the mantle of the planet.
And, as George Plafker realized, the exciting part was that if the causative fault was in fact dip-slip, there had to be some massive force pushing at least one of the two layers. The discovery of what that force was and how it operated might provide an element of proof of a new, evolving, and very controversial theory which would later be called plate tectonics.
There was another aspect to the mystery hidden beneath the surface of the Pacific. In Alaska’s case, a long trench in the seafloor (called the Aleutian Trench) ran to the south of the Aleutian island chain, paralleling the chain almost exactly from fifty miles offshore as it angled to the northeast toward the south-central Alaskan landscape. When Plafker had plotted out the raised area in Alaska and those parts which had been lowered, they formed a band of affected territory (and seafloor) which ran from southwest to northeast, paralleling the Aleutian Trench. Was that coincidence?
Plafker knew well the theory espoused by such masters of seismology as Hugo Benioff—a developing theory that such trenches are boundaries between sections of the earth’s crust, and that they most likely mark the spot where ocean floor is being shoved beneath an adjacent landmass. Benioff had published in 1954 a landmark paper which tracked earthquake hypocenters (a hypocenter is the exact spot and depth where an earthquake starts) from the ocean trenches landward at several different such spots on the globe. To everyone’s amazement, he found that when earthquake hypocenters were plotted in three dimensions, the greater the distance from the trench toward the continent, the deeper the hypocenters became. In fact, when drawn on graph paper from the side, his findings indicated a zone of earthquake activity from such trenches sloping downward beneath the landmass, which was labeled the “Benioff zone.” Could it be, he had asked, that the ocean floors were being consumed beneath the continents, and that the dipping layer of earthquake hypocenters he had identified revealed places where the layers above and the sliding layer below had snagged, then broken? If so, the prevailing model of the earth was all wrong.
George Plafker sat in the Chilean sun and watched one of his assistants working with a level, determining the exact height of a point on the distant cliff. The boat they had used to get here bobbed in the foreground in the bright sunlight, lending an almost Mediterranean feeling to the scene, even though the latitude was nearly forty-five degrees south.
These were very exciting times geologically. Plafker was glad in some respects that so much time had elapsed since the terrible death toll of the 1960 disaster here. It was hard to enjoy “good science” when so many had died or suffered. Yet enjoyment was exactly what he was deriving from finding further confirmation that on-site investigation—surficial evidence—could take a statistical ambiguity and resolve the conflict. What he was documenting here, like Alaska, had to be a dip-slip earthquake, caused by something shoving the floor of the Pacific under South America and Chile. Perhaps those who stayed in the lab and examined the numbers and the seismograms couldn’t tell what was happening, but here on the affected shoreline in person it was crystal clear.
He thought back to an incident of a few years before when he, an obscure geologist from Menlo Park, suddenly found himself unintentionally challenging the two-thousand-pound gorillas of the seismological world. He could laugh about it now, but at the time it had been unnerving. His definitive report on Alaska (a 1965 paper printed in Science magazine more than a year after the Good Friday quake) had taken careful issue with those scientists who thought a steep vertical fault had caused the great quake, and who, by inference, did not believe that the Pacific Ocean floor was pushing beneath the North American continent along south-central Alaska.
The problem was that the scientists with the opposing viewpoint included none other than Dr. Frank Press, one of the most respected seismologists and geophysicists on earth (based at Caltech), and Dr. Ari Ben-Menahem, a brilliant Israeli mathematician and seismologist (also at Caltech). Shortly after publication of the paper, New York Times science writer Walter Sullivan had interviewed Plafker at an East Coast symposium about his postulated model for the Alaska quake and how it implied that the radical new idea of plates slipping beneath other plates might be the cause, and how that differed from the other experts. Plafker talked freely, never dreaming that in bold headlines a few weeks later there would be a major story about the competition between two dynamically opposed theories, one espoused by Dr. George Plafker, the other by Dr. Frank Press.4
George Plafker was stunned. Here he was, a geologist who knew next to nothing about earthquakes and seismology, one who had never even studied an earthquake before the Alaska quake of 1964, and he had ended up constructing a model for the cause of the earthquakes that diametrically opposed the most brilliant and respected men in seismology.
Half hiding in his office at Menlo Park, George Plafker wasn’t entirely sure whether to be professionally proud or professionally frightened.5
But he was sure of his conclusions. While the others had relied on the ambiguous mathematical analysis of seismograms, he had pulled on his boots and walked the whole damned Alaskan countryside, documenting raised and lowered landscape that simply could not have been moved in such directions by a vertical fault.
And there was a larger issue than just the correctness of his Good Friday quake fault model. George Plafker’s conclusions about Alaska, and the curiosity which led him to the southern coast of Chile in 1968, were about to take on a pivotal role in changing the way earth scientists viewed the earth. His 1965 paper on the Good Friday quake was about to provide one of the last missing pieces to a global puzzle—the tectonic puzzle—which had been falling into place with accelerating rapidity since the early fifties. The science of seismology was soon to be catapulted into a brave new world of understanding in a blinding series of advances that would touch the lives of almost everyone on the planet.
Slowly, inexorably, like a recurring bad dream which begins to take on the trappings of reality, a new model of the earth had begun to creep into the periphery of earth science. It was a very troublesome model for many dedicated scientists because with each successive discovery, the traditional scientific model of the earth’s crust was beginning to crumble. The worst part was that the picture that was beginning to emerge from an increasing snowstorm of papers and articles bore a frightening resemblance to a heretical and thoroughly discredited idea first espoused in 1912, a postulation which had been received by the serious scientific community with univer
sal derision and scorn, and one which had been sneeringly dismissed as Wegener’s theory of continental drift.
It was a ludicrous idea. It was, said the leading scientists of the early twentieth century, a ridiculous manifestation of unprincipled and unfettered imagination. “It” was a theory dreamed up by an obscure German scientist, theorist, and meteorologist named Alfred Wegener, who had brazenly announced that the earth’s surface features were in constant horizontal motion.
The earth, in fact, was like a drying apple. That was the accepted view of the planet: a hot molten-rock interior covered by a thin, cooling crust, which over the eons had contracted as the crust had cooled, wrinkling and shearing into mountain ranges and valleys while collapsing and settling in spots during violent earthquakes.
But all that was primarily vertical motion. No right-thinking scientist would even laughingly propose that the major continents did anything but remain where they had first formed. Therefore, Alfred Wegener could not be a right-thinking scientist.
Wegener, a curious and energetic man trained in a variety of scientific fields, had found a naked emperor. The “accepted theory” of the cooling, drying apple could not explain why mountain ranges and vast plains were not evenly distributed worldwide. It failed to provide even a hint of explanation as to why the west coast of Africa seemed to fit the east coast of North and South America like pieces of a planetary jigsaw puzzle. And after some transoceanic investigation of the plant life and microbiology of both seashores (which turned out to be very similar on shores thousands of miles apart), Wegener began to look for reasons to believe that the continents, in fact, did move around.
From his early discomfort with the prevailing theories, Wegener, by 1912, had proceeded to what he called the theory of continental drift, a radical idea which he published in 1915 in a book entitled The Origin of Continents and Oceans, a book which emerged to the universal howls and abusive laughter of a scandalized world of scientists who knew that they already had the final answer, and a globeful of roaming continents was not a part of it.6
On Shaky Ground Page 16