A Crack in the Edge of the World

by Simon Winchester

  And they trend north and south because they are the result of collisions that occurred millions of years ago, either between three north-south-trending plate edges—those of the Pacific and Farallon and North American Plates, whose edges very roughly parallel the Oregon and California coastlines that exist today—or between their antecedents, that formed other oceans and other continents, such as Pangaea and Rodinia and Kenorland and all the other bodies and seas that composed the earth in times that, unlike mankind’s own history, were truly ancient. These bodies moved headlong into one another, banging, diving below, arching up, retreating, and banging into one another again, with one of the plates heading from the west toward the east, the other moving slowly but with immense and unstoppable power from the east toward the west. And all of these bodies and plates were compelled to move by the convection currents in the earth below, currents that are churning ceaselessly and that are making the plates execute these unending mazurkas and tarantellas up above on the mantle top.

  Nowhere is this more visibly true today than along the 750 miles of the San Andreas Fault, at the very western edge of the North American Plate, where it meets up with its neighbor plate that underlies the Pacific. The San Andreas Fault is young by the standards of the West, and very young by the standards of geology. But it is a very great deal older than America, older than California, and older than San Francisco, and it has been making its own kind of mischief for many millions of years past, and will continue to do so for many millions more to come.

  SEVEN

  The Mischief Maker

  The law against sodomy goes back fourteen

  hundred years to the Emperor Justinian, who felt

  that there should be such a law because, as

  everyone knew, sodomy was the principal cause of

  earthquakes. “Sodomy” gets them. For elderly,

  good-hearted audiences, I paraphrase; the word is

  not used. College groups get a fuller discussion of

  Justinian and his peculiar law, complete with

  quotations from Procopius. California audiences

  living on or near the San Andreas Fault laugh the

  loudest—and the most nervously. No wonder.

  GORE VIDAL, Matters of Fact and Fiction, 1977

  AT A QUARTER PAST TEN ON THE MORNING OF SEPTEMBER 28, 2004, a woman named Christy Gieseke was taking a shower on her horse farm in San Miguel, in the vineyard country of central California. Suddenly the house began to shake violently. Ms. Gieseke ran out of the bathroom, noticed that the living-room chandelier was shimmying dramatically on its chains, decided to run, and eventually made it, unscathed, into the open air. Her dog, a usually well-tempered Rhodesian ridgeback, was panicking, running wildly across the yard, barking madly. But her horses, which she might have supposed would be bucking in panic, were by contrast unusually and strangely quiet—stunned, perhaps, by this inexplicably frightening set of circumstances.

  After only a few more seconds, the shuddering, and the barrage of curious creaking and cracking sounds from the very earth itself, came to an abrupt halt. The event was, at least for the time being, quite over. The horses began to graze peacefully once again, pawing the ground with their hooves by way of seeming remonstrance; the chandelier’s swaying slowed, then stopped completely; and whatever growling sound had welled up from the ground faded to mere white noise, and then was gone altogether.

  It was at this point that Christy Gieseke realized that she had dashed into her garden quite naked but for a dishtowel she had grabbed in the kitchen on the way through. She ran back into the house, found her clothes—and hoped that would be the end of it. Earthquakes tend to make people nervous—and to behave spontaneously, even in a place as accustomed to the earth’s violent movements as San Miguel, California, and the rather more notorious neighboring towns of Paso Robles and Parkfield.

  This, as the locals like to say, is earthquake country. San Miguel, hilly, pretty, moneyed—horse ranches, wineries, and exemplary weather—suffers from a ceaseless onslaught of small seismic events, to which many of the locals have become almost entirely inured. Once in a while a larger earthquake strikes. The last of major significance hit just before Christmas in 2003; it killed two people in Paso Robles, toppled a church tower there, and did grave damage to the 200-year-old Mission San Miguel nearby.*

  But let us concentrate on the event of September 28. Ms. Gieseke and her horses; a vineyard owner named Harry Miller, who observed “trees shaking like brooms, and dust coming everywhere,” as 300 cases of wine stored in his cellar were upset and jets of water were sent spouting thirty feet into the air from his tank; and the 9,000 Californians living between Sacramento and Santa Ana who are officially recorded as having felt the event—all were affected by what is now as properly and fully annotated a disturbance of the earth as has ever been known.

  Its first shock—the mainshock, as the originating shock of an event is known—struck at 24 seconds past 5:15 P.M., Coordinated Universal Time, or 24 seconds past 10:15 A.M. Pacific Daylight Time. The shock produced a strong shaking that lasted for almost exactly 10 seconds, and it was followed by a series of some 161 aftershocks. The event’s epicenter—the point on the earth above which the shock-inducing rock rupture occurred—was seven miles southeast of the village of Parkfield. The hypocenter—the subterranean point where the rupture took place—was a little less than five miles down.

  Once the rock had ruptured the shocks then traveled, and at a fantastic speed, in a northwesterly direction, disturbing people—Mr. Miller and Ms. Gieseke among them—in the myriad ways that a shock as impressive as this one can. The formal classifying number of the event (or the eq, as such happenings are generally known in the seismological community) was NC51147892, with the NC being the internationally recognized two-letter code for the Northern California Regional Seismic Network, based at the U.S. Geological Survey headquarters at Menlo Park, at the upper end of Silicon Valley. The regional moment magnitude of the quake, which is what is usually calculated and released to the press, was 6.0.* No one was hurt by it, nor was there any but the most mildly inconvenient damage.

  In normal circumstances, and in most places, this would have been a merely moderately significant event. But the circumstances, and the place, were anything but normal—and as it happens, the event of the September 28, 2004, was probably more measured a seismic happening than had ever been recorded in the history of this planet. And that is because the event took place very close to this otherwise memorably forgettable little Californian settlement named Parkfield.

  Parkfield, California—a sleepy, dusty farming town that nestles among rolling hills fifteen miles to the northeast of Christy Gieseke’s home—enjoys a peculiar reputation in world seismic lore. It may not suffer most from a superabundance of seismic activity—that record, for what it is worth, appears to be held by a faraway and rather tumbledown Californian village called Petrolia, which has earthquakes almost every other hour—but it is the place that suffers most from a superabundance of seismic science. For it has had so very many measurable earthquakes (dozens of very small ones every week, and larger tremors that are substantial enough to be felt by reasonably aware humans several times a year, and those of a magnitude to drive women from their showers every two or three decades) that in the last years of the twentieth century a program was begun that made sure that every Parkfield hillside and valley and suspicious-looking outcrop or knoll or riverbed was covered with an array of earthquake-detecting instruments. These have become more sophisticated, delicate, and expensive as the years and science have worn on.

  Anyone who makes it to this tiny town rapidly becomes aware that it is a much-measured place. Beside the roads, up on the hilltops, lurking in groves of trees, and in strange boxes with menacing locks and orange notices that warn of the not-so-dire federal penalties awaiting those who interfere, are the devices that monitor, hour by hour and, in some cases, millisecond by millisecond, what happens below the earth around Parkf
ield. A photocopied guide handed to visitors relates the kind of thing: “on your right, look for a 4' X 4' X 4' structure … this contains a seismometer,” “on the south side of the road there is a piece of PVC pipe sticking out of the ground with the letters JPL-GPS—this belong to the Jet Propulsion Lab,” “on the left side is a USGS creep-meter … do not touch the thin metal wire.”

  The data from the machines is broadcast to thousands out in the seismically fascinated world. Some is sent via tiny satellite aerials to Colorado, some goes to a university near San Diego, still more to the Geological Survey’s regional headquarters at Menlo Park, while other parcels of information are flashed to monitors in Pennsylvania, North Carolina, Oxford, London, and Brisbane. Parkfield may be a town very little known in most of the rest of lay California, but to members of the geological priesthood with a keen interest in how the world is believed to work, it is the center of the seismic universe.

  Though Parkfield is no Grand Canyon, the local residents know they are onto a good thing. So the town’s café, across the dusty street from a hotel made of logs, sports a water tower painted with the slogan BE HERE WHEN IT HAPPENS, and the hotel tries to tempt passersby with SLEEP HERE WHEN IT HAPPENS. On the menu is a steak called the Big One, as well as a rather more modest version called the Magnitude Six; and the desserts are called Aftershocks. A sign nailed to a tree offers eggs produced by an evidently surprised chicken shown being shaken awake; and there are a handful of memorials and notices and walking trails that remind people of the dramatic moments to which this town is prone.

  At the southern entrance to Parkfield is a white-painted iron highway bridge that takes the road across the oak-shaded and occasional stream known as the Cholame Creek. Anyone crossing the bridge will notice that it is spectacularly bent: The metal rails and supports all veer off to the right by well over a foot and a half. Moreover, there are patches of freshish asphalt on the pavement, where repairs have been made by CalTrans, the authority that fixes damaged state roads, and whose crews doubtless sigh whenever they hear of fresh earthquake activity up at Parkfield. The event that pitched Ms. Gieseke from her shower moved large chunks of concrete off their foundations and opened up a new gap several inches wide. For a time the bridge was closed, yet again, while the asphalters did their stuff. By measuring the bridge—and people have been doing this for many years, especially since it was particularly badly damaged by an earthquake in 1966—it can be shown that the abutments have moved more than five feet since the structure was built in 1936: The westernmost abutment, the side farthest away from Parkfield, has moved to the north, while the side closer to town has slid down toward the south.

  The little iron bridge and the half-dry creek serve as all-too-visible reminders of just why it is that Parkfield occupies the place that it does in the seismic canon. For the creek marks the very edge of the North American tectonic plate, and is the center of the narrow zone that shows where the next-door Pacific tectonic plate butts up against it, and lurches and slides northward along it with predictable unpredictability.

  SOME CHAPTERS BACK we began a long journey clear across the full expanse of the North American Plate. It was a journey that started in a valley in the center of Iceland, where a line of cliffs marks the plate’s far eastern edge. Here, in the middle of this very ordinary-looking Parkfield town bridge, is the point that marks its extreme end—the plate’s western edge, where it rubs against its Pacific neighbor. Central Iceland is divided from central California by 6,000 miles—a distance that marks, at this place in the world, the width of the entirety of one of the greatest and most important geological entities of all.

  THE ABUTMENT of the bridge that stands closer to Parkfield is on the massive North American Plate; the abutment on the other end stands on the Pacific Plate, the equally massive and ever-moving part of the world that underlies such faraway places as Hawaii and Tonga, Pitcairn Island, Easter Island, and the South Island of New Zealand. Another part of the world begins right here. And the line that divides the two plates, the place that geologists like to call the plate abutment, or the plate boundary, coincides with the visible surface manifestation of what is perhaps the best-known geological fault that can be seen anywhere.

  The line is some 750 miles long. It curves sinuously, in the shape of an elongated boomerang, from where it makes its landfall on an unstable clifftop up in Humboldt County, in the wet and windy north of California, to where it dives into the heart of the earth in a hot and muddy field beside a hissing geothermal plant, down by the fences and well-armed border guards at the Mexican frontier. The town of Parkfield lies almost halfway along the line; the buckled bridge is buckled because although it, too, is sited on the fault, it cannot be said to lie along it, but rather to lie across it, since the road in and out of Parkfield needed to cross from one side to the other. And it is axiomatic that any structure that is built across a fault like this is placed under enormous stress whenever the fault moves—something that this one does, uniquely, all the time.

  Shifting, sliding, vibration, destruction—everything about this 750-mile-long line suggests that we are dealing with a living, breathing, ever-evolving giant that slumbers lightly under the earth’s surface and stirs, dangerously and often, according to its own whims and its own rules. At almost every single place where the line can be traced there is evidence of movement, damage, some kind of mysteriously infuriating life. The bending of the Parkfield bridge is one instance, as is the crumbling instability of the sea cliffs up in Humboldt County where the fault first comes ashore; the regurgitating steam that hisses around that muddy southern field is another, as is every earthquake that is measured every day in the Cholame Valley, like the one that drove Christy Gieseke from her shower in San Miguel, like the one that knocked down the nearby mission some years before, and like hundreds of others besides.

  And, while there have been countless other shakings and vibrations randomly scattered across the American West, once a series of systematic studies of California’s seismicity had been made a century or so ago, a very obvious pattern soon emerged along this line. There seemed to be much more movement and nuisance of one kind or another along it than anywhere else in the state.

  The activity was first noted as being concentrated in a valley south of San Francisco, which lay right on top of the line. This valley had been named the Valle de San Andreas by its Spanish discoverer, because he found it on November 30, 1774, the feast day of the apostle most English-speakers (like most Russians) know as Saint Andrew. Once it was realized that the valley lay on (and indeed was caused by) the very fault line where all this activity was concentrated, the fault itself was given the name of the valley: It became the San Andreas Fault.*

  The San Andreas Fault is a feature so well known to geologists around the world that it is generally referred to by its initials, SAF. More important for this account, movement along the San Andreas Fault was the fundamental event that all but destroyed San Francisco in 1906. It is also the phenomenon that, on some unpredictable day in the future near or distant, will surely destroy any city built by those improvident enough to site it nearby.

  THE STORY OF THE BIRTH of the San Andreas Fault is far from simple, and interpretations change as new information is uncovered. It can be summarized, however, and in essence it appears that the mechanisms that gave rise to the fault can conveniently be said to have begun about 150 million years ago, out on the edges of a Pacific Ocean that was very much larger than it is today.

  A submarine chart of the ocean today shows a line of relatively shallow water that extends southward for several thousand miles from a point close to the west coast of Mexico, via the Galápagos Islands and Easter Island and the Juan Fernandez Islands,* all the way down to the Antarctic. The island groups that lie along it are volcanoes, some active and some not; these, and the submarine ridge of which they are the visible peaks, are the manifestations (just as the Mid-Atlantic Ridge is a manifestation on the farther side of the world) of a part of the earth tha
t is splitting open, where plates are moving away from each other, and where new material is being oozed out onto the planetary surface (in this case most of it invisibly, beneath the sea). The ridge is called the East Pacific Rise—not least because it is the dominant feature of the eastern half of the Pacific Ocean.

  But 150 million years ago it was not in the east: It was much more in the middle of what in those days was the very much wider Pacific. And just like the Mid-Atlantic Ridge, this then Mid-Pacific Ridge was also a spreading zone, a place where two tectonic plates were moving steadily away from each other. The plate on the western side of the ridge was the Pacific Plate that we know today, and it was moving northwestward. The plate on the eastern side of the ridge, which geologists have named the Farallon Plate, was moving southeastward. To complicate matters further, the North American Plate, which was being forced by pressure from the upwelling of magma at its eastern edge, at the Mid-Atlantic Ridge, was shifting steadily westward, in the direction of these two spreading plates, the Pacific and the Farallon.

  The consequence of movements like this one—the collision of the North American and Farallon Plates—is the familiar one of subduction, the phenomenon that is known in every corner of the world where there are active and very violent volcanoes, from Java and Sumatra to Japan, from Kamchatka and New Zealand to Alaska—places where a light continental plate hits a heavy oceanic plate square on, and the heavier plate is subducted beneath its continental collision partner. Wherever such a collision takes place, volcanoes and earthquakes are created and break out in dangerous abundance. In this case the heavy and oceanic Farallon Plate subducted below the light and continental North American Plate—causing many of the geological features, Eldridge Moores’s ophiolite sequence in particular, that make up the American West.

  The North American Plate’s westward movement continued until, sometime around 30 million years ago, it hit a snag: It ran into the selfsame East Pacific Rise. The rise then began subducting below the North American Plate as well—and this created the kind of tectonic confusion that is much better seen on a pool table. (Physicists with a penchant for divining the way that a number of colliding forces all moving in different directions can impinge on and interact with one another work out this kind of thing mathematically; in The Hustler, which some say it parallels, it was more a matter of intuition, and gin.)