Cascadia's Fault Page 6
Measurements were made by a network of seismic stations around the globe, but again—because none of the instruments on the ground in Alaska had survived long enough to capture an accurate local record of the energy—there were discrepancies in Richter scale calculations as well. A report prepared by the U.S. National Research Council lamented that the seismographic record of this earthquake was “woefully incomplete.” Some seismologists figured the magnitude was 8.3; others pegged it at 8.6. Part of the problem was the Richter scale itself.
As one geologist explained it to me, no seismograph in the world at that time could get a correct magnitude because—until digital seismographs came along—the entire earthquake spectrum could not be accurately recorded for any event that lasted longer than about a hundred seconds. Great earthquakes like this one can take as long as three hundred seconds, sometimes even more, to finish rupturing. At an average velocity of just over 1.8 miles (3 km) per second, that’s how long it would take for a fracture like this to unzip over such a long distance.
Basically, the old Richter scale was good only for shocks up to about magnitude 8; anything bigger (or longer lasting) was off the scale, so to speak. So an extension of the scale—the moment magnitude scale—had to be devised for measuring the relative sizes of the 8+ events. Thus the Alaska temblor was eventually assigned a magnitude of 9.2 while assessment of the Chile quake of 1960 shifted from 8.9 to 9.5, the largest earthquake ever recorded with modern equipment. The point being that no matter how the numbers are crunched, the Good Friday earthquake was then and remains the largest scientifically documented seismic shock to hit continental North America and the second largest in the world.
Piecing together a sequence of events in the days and weeks after the Easter weekend, scientists concluded that the zone of significant damage covered 50,000 square miles (130,000 km2). The vibrations were felt over an area of 500,000 square miles (1.3 million km2). The pulses of energy had traveled roughly 1,200 miles (1,930 km) to the southeast, when a group of scientists attending the annual conference of the Geological Society of America, who were enjoying dinner in the revolving restaurant atop Seattle’s Space Needle, felt the tower vibrate slightly.
Barometers in La Jolla, California, roughly two thousand miles (3,200 km) from Anchorage, detected an atmospheric pressure wave generated by the quake. Water levels in 650 wells across North America, in Hawaii, and as far away as South Africa jumped abruptly, one as much as seventeen feet (5 m). The Council report said “probably twice as much energy was released by the Alaska earthquake as by the one that rocked San Francisco in 1906.” Measured by the newer moment magnitude scale, Alaska 1964 was 160 times larger than San Francisco 1906.
In the immediate aftermath of Good Friday, however, reports of casualties and property damage were slow in reaching the outside world because power and telephone lines were down all over south-central Alaska. Only those living through the disaster knew how bad things really were. The statewide death toll, at 115, would be described officially as “very small for an earthquake of this magnitude.” Of those who died, 106 were killed by the tsunamis. But in some ways, the people of Alaska had shared a bit of the luck that blessed their neighbors down in Port Alberni.
Consider the element of timing. The rupture happened late on a holiday Friday afternoon, the beginning of Easter weekend, so schools were empty and most offices were deserted. Construction crews working on the new Four Seasons building in Anchorage had packed up and gone home only thirty minutes before the earth began to shudder. The unfinished and fortunately unoccupied high-rise collapsed in a heap of buckled concrete and twisted steel.
At the moment of the rupture hundreds of trollers and seiners were tied up and dozens of canneries were shut down because fishing season had not yet opened. As luck would have it, the tide that afternoon was among the lowest of the year, so the reach and hydraulic impact of the tsunami was somewhat reduced. Imagine what might have happened along the docks and boat harbors in the middle of a busy workday on a swollen tide in high season.
Although snow blanketed the mountain slopes and still covered the ground in many places even at sea level, the temperature had been pleasantly mild that afternoon, with highs near forty degrees Fahrenheit (about 4°C). But weather-wise Alaskans were still dressed for the most part in warm clothing, which no doubt helped them survive a long, cold night outdoors or until they made their way to rescue shelters. Of all the things that could have gone wrong, not all of them did.
Alaska was and still is a sparsely populated frontier; an event of this magnitude in southern California would have been catastrophic in terms of deaths and injuries. But to those who survived, numerical comparisons are meaningless. No matter how lucky they were, most Alaskans were devastated by the earth’s staggering convulsion. To them Good Friday was every bit as traumatic as anything that has happened in L.A. or San Francisco. Hundreds of homes were damaged or destroyed in communities all along the south coast. In several waterfront towns large oil storage tanks ruptured and caught fire, spreading a blanket of flames across the tops of incoming tsunami waves.
In Anchorage, a multistory apartment block and a big department store collapsed. Yawning cracks opened in downtown streets and slabs of falling concrete crushed cars like pop cans. Outside the city, in a neighborhood called Turnagain Heights, built on a clay bluff with spectacular views of the sea, the earth split open in dozens of places. The ground slumped, houses caved in, and people fell into a maze of crushed timbers and fissures that opened and closed in the liquefied clay.
As the land heaved and bucked, railway tracks got twisted and humped, highways cracked, and bridges were yanked apart. Docks and port facilities in Whittier, Cordova, and Homer were smashed by incoming swells. Undersea landslides created local tsunamis that struck tens of minutes before the main tsunamis arrived from offshore. A wall of seawater fifty feet high (15 m) slammed the vital seaport of Seward, road and rail gateway to Alaska’s interior. Most of downtown Kodiak was inundated; the entire port city of Valdez was wrecked and would have to be relocated.
Later that night a radio operator aboard the oil tanker Alaska Standard tapped a frantic message in Morse code that said, “Seward is burning.” Ham radio operators working from mobile units in their cars finally reached the outside world with fragmented reports of whole towns “wiped out by a great tsunami!” In the end, giant waves took the most lives while rock and mudslides and twisted, heaved, and fractured slabs of solid ground caused the greatest physical damage.
Alaska had always been a rough and tumble, seismically active kind of place, and longtime residents had grown used to the almost constant rumblings of nature. But there had never been one quite like this. Even scientists who knew the most about the state’s geology were puzzled because nobody could say for sure which fault had broken or how it had gone undetected for so many years.
In a series of urgent phone calls late that Friday night, officials at the U.S. Geological Survey decided they needed to know where and how the earth had fractured and how a fault could lie silent, almost as if it were dormant, while storing massive amounts of energy for perhaps hundreds of years before ripping apart in a megathrust earthquake. Famous faults like the San Andreas and many of its lesser known cousins are obviously moving—creeping and slipping and breaking—somewhere almost all the time. Like schoolyard bullies, you always know they’re not far away and could cause trouble at any moment. But for a really big fault to do nothing in all of recorded history and then suddenly rip itself apart—that was a mystery that had to be solved as quickly as possible.
Something very much like this had happened off the coast of Chile only four years earlier, in 1960. That event too was a mystery because scientists still did not know what had caused it—the biggest temblor of all. But first, and most immediately, they had to find out exactly what had happened in Prince William Sound.
CHAPTER 4
Against the Wind of Convention: Plafker, Benioff, and Press
On S
aturday morning, March 28, 1964, thirty-five-year-old geologist George Plafker made a hasty exit from the conference in Seattle to join a team of USGS scientists dispatched to Alaska for a rapid investigation of the earthquake. He and colleague Arthur Grantz from the main West Coast laboratory in Menlo Park, California, wanted to see first-hand what had happened to the landscape—everything from rock and mudslides to compaction of the ground, the liquefaction of soils, the heaving up or dropping down of sections of land, and the effects of tsunami waves—all before anything changed or was cleaned up. They were also hoping to find the unknown fault that had torn the land apart and clues that might explain “the mechanism” of the rupture—how and why it happened.
Local officials in Alaska and U.S. military officers involved in the rescue and recovery effort wanted a quick damage survey that would warn them of any unfinished landslides, avalanches, or rivers that had been dammed by landslides—anything that might cause still more havoc and destruction. What they wanted to know more than anything else was whether the shaking was over yet. And if not, when might it start again?
Within twenty-four hours of the main shock, there had already been at least ten aftershocks of magnitude 6, along with dozens of smaller but nonetheless nerve-rattling vibrations. Seismometers would eventually log twelve thousand aftershocks in the first sixty-nine days after Good Friday. But any reputable scientist knows there is no simple answer to the question of when the next tremor might come. In this case they couldn’t even say for sure what had caused the main event.
Plafker saw some of the worst devastation right away in the bluffs around Anchorage, along Turnagain Arm and near the harbor at Fish Creek. The land underneath had liquefied, causing the surface to fracture into blocks. “There were these large areas along the bluffs that had just kind of slipped seaward,” he recalled. “They’d broken up—the blocks at the surface broke up and tilted. And there were several people killed . . . It was pretty overwhelming.”
At the very least, Plafker and his colleagues figured they would be able to provide a detailed description of what the temblor had done to the surface of the land and which way the fault had come unstuck—assuming they could find it. What started out as a one-week reconnaissance mission to determine the scale of the thing turned into a summer-long operation requiring a whole team of USGS personnel to catalog and research the devastating aftereffects.
They hitched rides on airplanes and helicopters borrowed from the military and flew hundreds of miles along the coast, making detailed descriptions of a torn and ravaged land, searching all the time for evidence of a major fault. The shaking had triggered a series of long, jagged rockslides that left gaping scars on the slopes of heavily forested mountains. There were open fissures and heaved-up slabs of rock in several segments along these smaller escarpments. But there was no sign of a much bigger fault—no continuous rupture in the earth’s crust, nothing obvious enough from the air to have caused an earthquake this widespread and violent.
Hundreds of seismometers around the world had recorded the shockwaves from Prince William Sound, and early calculations pointed searchers toward a small glacial fjord in the mountain shoreline called Unakwik Inlet. Somewhere twelve to thirty miles (20–50 km) underground was the “focus,” or starting point of the main rupture. Directly above the focus, where a vertical line would meet the surface of the earth, was the epicenter. But the epicenter was a problem; there was nothing to see, no physical damage to the surface that common sense would tell you ought to be there after one of the biggest earthquakes in the world had just broken the place apart.
Plafker’s first impression was that the rupture zone lay hidden beneath new snow or was perhaps somewhere offshore. Several new science papers resurrecting the old theory of continental drift had been published only two years earlier and were still the source of controversy and buzz, but the exciting idea that a slab of the Pacific Ocean floor might be sliding underneath the state of Alaska might explain why the fault was not visible from the surface.
As the investigation continued, Plafker hiked the shoreline to take detailed measurements of vertical changes in the level of the land. What he discovered was truly astonishing. A segment of the earth’s crust 430 to 500 miles long and 90 to 125 miles wide (700–800 km by 145–200 km) had been “deformed” by the earthquake. An area roughly the size of Washington and Oregon combined had been either heaved up or dropped down—“larger than any such area known to be associated with a single earthquake in historic times,” he later wrote.
Somewhere between 66,000 and 77,000 square miles (170,000–200,000 km2) of the ocean floor had been hoisted up, while vast areas of dry ground inland (behind the beach zones) had sunk. The sea floor southwest of Montague Island appeared to have been lifted more than fifty feet (15 m). The sudden upthrust of the ocean bottom was clearly what had displaced so much seawater and created the deadly tsunamis that hit Port Alberni and the West Coast.
Wearing gumboots and hauling a surveyor’s level across the slippery rocks, Plafker spent most of that summer in Alaska making more than eight hundred separate measurements of uplift or subsidence (relative to sea level) along thousands of miles of shoreline between Bering Glacier and the Kodiak Islands. In some places he didn’t need equipment to see what had happened. He could tell how far a beach had been raised simply by examining the whitish band of dead barnacles, algae, and mussels that had been killed when seafloor rocks were lifted above the reach of tides. Without their daily slosh from the ocean, all the sea creatures clinging to those heaved-up rocks had died and been bleached by the sun. Their reeking bodies painted a marker line on the rocks that measured how much the earth had moved.
In other places, where the ground had subsided, he found bands of dead brush that had been killed by seawater. As the incoming tides extended their reach over newly sunken beaches and marshes, the salt was slowly poisoning huge shoreline trees that once had lived above the tides altogether. It would take a while for the big trees along the beach to die and wither, but their mossy hulks standing in knee-deep, newly created saltwater lagoons would become vital clues in a later investigation.
Plafker found hoisted sea cliffs, drained lagoons, new reefs and islands—all indications of violent and widespread upheaval. A short time later another crucial piece of the puzzle came from the USGS survey crew, who rechecked a network of triangulation points and discovered that the earth’s surface had also been stretched horizontally as much as sixty-four feet (20 m) between Anchorage and the outer island of Prince William Sound. This extraordinary piece of geographic distortion would eventually help prove what kind of rupture this really was and why nobody could see the fault from the surface.
Plotting his elevation numbers on a map, Plafker also noticed an invisible line of “zero change” in the level of land, approximately parallel to the south coast mountain ranges and to the deep Aleutian Trench offshore. On the seaward side of this invisible line, the land had been raised; on the landward side it had dropped down. “What I was doing was just trying to get some feeling for whether these areas of uplifted and subsided ground might be pointing to a fault in between them,” he told me.
If there was a hidden crack in the earth, it seemed odd that heaving up and dropping down—especially on a scale as grand as this—could have happened without breaking the surface. How could so much land be jacked up or slumped with no visible fracture line? And yet “we never could see the fault,” he said, and that made the Alaska mystery all the more fascinating.
In numerous places he saw the “squeezing up of the rocks,” which he likened to a crumpled fender. It all looked very different from the kinds of surface damage he’d seen when plates slid past each other along a fault like the San Andreas. In California the earth was fractured vertically—and it was plain to see—but in Alaska the rocks were being folded up and shortened. Or stretched horizontally like taffy.
The essential unknown of the Good Friday rupture—the true nature of the fault—needed an explanatio
n, so Plafker and his colleagues spent months living on a converted river tugboat, prowling the shore in small skiffs, measuring rocks and crunching numbers trying to make sense of what they’d found. Their data logs were so chock-full of bewildering new information it would take until June the following year to get it organized and published.
To make the job more challenging, Plafker, a relatively young scientist who had not yet earned his PhD, was preparing a report about earthquakes—not his chosen specialty. He was a geologist who’d spent most of his career up to that point mapping rock formations, searching for oil and other natural resources. He was not trained as a seismologist, yet here he was writing about an unseen fault that had behaved contrary to what most experts in the field were familiar with. This invisible crack along the Alaska coast appeared so unlike the San Andreas that the facts and figures Plafker came back with beggared belief. And got him into a bit of hot water.
The new science that would eventually explain what happened in Alaska—the revolution in geology now known as plate tectonics—was in mid-evolution in 1964. The controversial theories had not been refined, tested, or accepted. “They were still just barely getting to it at the time of the earthquake,” recalled Plafker. Strange as it may seem today, there was no broad consensus then on how mountains and volcanoes were formed or what kinds of forces generated earth tremors. Geophysicists didn’t even know for sure whether faults caused earthquakes or, the other way around, earthquakes caused faults. Was the earth’s surface cooling and shrinking and cracking? Or was it expanding and cracking because of radioactive heat from the deep interior of the planet? All these big ideas were still very much in play.