1). What are the boundary types? Strong ground motion at Seward lasted 3-4 minutes. The tidal wave had diminished by the time it hit Hawaii and Japan, causing little damage. The plate boundary is a broad zone of deformation with a width of about 60 miles (100 kilometers). Downtown Anchorage had the most property damage mainly due to immense landslides, one of which dropped the business district nine feet. For example, rocks found today in Point Reyes National Seashore north of San Francisco were originally part of the line of granite rocks formed beneath ancient subduction zone volcanoes. When two plates are moving away from each other, we call this a divergent plate boundary. This Story map combines an interactive map with historic photos of the earthquake. The duration of strain accumulation in the epicentral region, as interpreted from the time interval during which the coastal submergence occurred, probably is 9301,360 years. Each giant slab was expected to be moving slowly. It explains how the continents and oceans have been shaped, and why there are earthquakes, mountains, volcanoes and tsunamis. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. The 1964 earthquake in Anchorage, Alaska occurred as a result of an oceanic plate sinking under a continental or land plate. Quake leaves destruction, fear. Science News for Students. This megathrust fault has been the source of many large earthquakes including the 1964 Alaskan earthquake that registered a magnitude 9.2 and remains the second largest earthquake in . The earthquake rupture started approximately 25 km beneath the surface, with its epicenter about 6 miles (10 km) east of the mouth of College Fiord, 56 miles (90 km) west of Valdez and 75 miles (120 km) east of Anchorage. And it moved parts of the Alaskan coast 15 meters (50 feet) toward the sea. Every century or so a large earthquake is necessary to release stress accumulated along large segments of the San Andreas Fault that lock rather than slip smoothly. Georges interpretation of this as a subduction zone was a real key, says Gary Fuis. Some had been up to 24 inches (61 centimeters) in diameter and as much as 101 feet (30.8 meters) above sea level. Relatively few earthquakes occur in intraplate environments; most occur on faults near plate margins. Along much of the boundary, the bulk of the motion occurs along the San Andreas Fault. Learn about the Great Alaska Earthquake of 1964 in this video adapted from the Valdez Museum & Historical Archive. Finally, the pressure between the plates is so great that they break loose.