Free Cascadia's Fault by Jerry Thompson Page B

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 km 2 ) 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