Lucky for this team, 70 new seismographs (SIZE moh grafs) had recently been installed all over the world. In particular, “We were looking for evidence of surface faulting,” he recalled at a press briefing earlier this week. Plafker’s team mapped all the changes triggered by the quake that they could find. The epicenter is that X-marks-the-spot site where the tremors commenced. They also sought to locate the quake’s epicenter. One was figuring out why some parts of Alaska had risen as much as 11.5 meters (38 feet), while the ground at other sites had dropped, or subsided. They knew earthquakes develop when shifts occur along underground fractures, called faults. Their mission: Figure out what had just happened. He and two of his colleagues flew up, landing at an Air Force base outside Anchorage, Alaska, just a day after the main shaking stopped. Geologist George Plafker worked for the USGS near San Francisco, Calif. Map showing plate boundaries that were active during the 1964 Great Quake. But it took some geological sleuthing to determine how and why. Some start and then stop, only to start again much later.Įarth definitely moved with a start during the 1964 quake. The friction between these massive plates means they don’t move fast. At still others, known as transform boundaries, plates slide past each other. Along other, divergent boundaries, plates move away from each other. Along convergent boundaries, neighboring plates either collide head-on or a denser ocean plate dives beneath a lighter continental plate. Scientists now classify the bumping and grinding between plates in three different ways. But they could also be explained by other things.’” Back then, he points out: “There was no smoking gun yet.” “Before the 1964 quake,” he recalls, “you could look at features and say ‘Yes, these could be explained by plate tectonics. It was only after the 1964 quake, he says, that scientists could definitively point to the effects plate movements on Earth’s surface. USGS/Nat’l Park ServiceĪs Alaska’s state seismologist, Mike West studies earthquakes. Most plates (like the North American one) span both land and seafloor regions. The fastest plate ‘race’ at 15 centimeters (6 inches) per year The slowest creep along at fewer than 2.5 centimeters a year. These tectonic plates move gradually, bumping and grinding against each other.Ī map of some dozen major tectonic plates and several minor ones. Plates beneath the oceans are much thinner than those under continents. Their thickness ranges from 80 to 200 kilometers (50 to 124 miles). It includes the crust and uppermost mantle.) Depending on how you count them, there are about 12 main tectonic plates, and numerous smaller ones. (The lithosphere is Earth’s outer solid layer. Like a jigsaw puzzle, Earth’s lithosphere is divided into interlocking pieces, called plates. Now, 50 years later, plate tectonics is no longer a clever hypothesis. Each giant slab was expected to be moving slowly. It held that Earth’s uppermost layer, called the lithosphere, is broken into enormous pieces. In 1964, plate tectonics still was just an emerging - if unproven - concept. And it has forever changed what scientists understand about the constant remodeling of Earth’s surface. The reason: This quake opened a new era in geology.
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Now, a full half-century after Alaska’s gigantic quake, geologists are still feeling its effects. The only stronger trembling ever recorded was a magnitude-9.5 monster that shook Chile in May 1960. The Great Alaskan Earthquake was a magnitude-9.2 event. Similar sloshing swamped fishing boats in Louisiana. Quake effects were felt in nearly every state.In Washington, Seattle’s Space Needle swayed like a tree in the wind. Underwater landslides along the Seward, Alaska, waterfront triggered the strong waves which hit here, 2 miles (3.2 kilometers) from Seward. The yellow cab of the truck wrapped around the right side of a tree its wheels around the left side. This vehicle illustrates the force of the tsunami waves that had struck this truck, which had been 32 feet (9.8 meters) above sea level at the time of the quake. Indeed, like ripples in a pond, a tsunami travels outward in all directions. Most had been killed by the tsunami waves that raked not just the coast of Alaska, but Oregon and California too. No Alaskan who survived would ever forget this day. They washed away everything in their immediate path - buildings, docks and people. In places, the waves towered as high as a 20-story building. Together, these destructive waves swept Alaska’s coastline with devastating speed and power. Lost ark giant whirlpool.Explainer: Telling a tsunami from a seiche