60 Years Ago, the Largest Earthquake in U.S. History Astonished Geologists.
This natural disaster continues to drive scientific discoveries in today’s world.
From Theory to Reality
The earthquake is evidence for the plate tectonics theory.
On March 27, 1964, the largest earthquake in U.S. history and the second strongest in the world struck Alaska with a magnitude of 9.2 on the Richter scale. In Anchorage, streets were split apart, and even an entire neighborhood sank into the sea.
Along the Alaskan coast, massive tsunamis destroyed ports and swept away many villages. Businesses relocated, residents were forced to evacuate and rebuild. The disaster caused $3 billion in damages across the state.
However, perhaps the most significant and long-lasting impact of the earthquake was on science. This disaster reshaped humanity’s understanding of earthquakes, tsunamis, and the land beneath our feet. Today, scientists continue to study the effects of the earthquake on the natural world.
Immediately following the disaster, the U.S. Geological Survey dispatched field geologists to Alaska to investigate the earthquake’s origins. For weeks and months, scientists carefully measured the impact on the landscape and discovered vast areas of Alaska had experienced permanent uplift or subsidence as the ground shook.
For instance, a section of coastline near Kodiak rose by about 9 meters. More than 300 kilometers northeast of Anchorage, the land sank approximately 3 meters. This evidence was the first concrete proof of plate tectonics. According to this theory, the Earth’s crust is made up of tectonic plates that are not stationary but move. Earthquakes cause these plates to collide, separate, or overlap.
Before the 1964 earthquake, scientists lacked the necessary data to prove the existence of subduction zones, where one tectonic plate sinks beneath another. But after the earthquake, they had clear evidence of plate tectonics.
Using ideas about plate tectonics and data on uplift and subsidence, geologists traced back to accurately identify two tectonic plates that had slipped 18 meters along the subduction zone, causing the earthquake. Scientists also made significant advances in geophysics, helping them understand the Earth’s movement processes.
Researchers are building a global network of seismometers to measure ground movement and monitor nuclear weapon tests. These tools also have the added benefit of collecting data on earthquakes.
Additionally, researchers developed techniques to date similar rock types found on different continents, proving that they had separated and moved vast distances across tectonic plates over millions of years.
Since the emergence of this technology, scientists have discovered numerous subduction zones in Indonesia, Japan, and Chile—areas that would later experience significant earthquakes. “I think it is fair to say that the 1964 earthquake was a significant part of the transition from the theory of plate tectonics to the reality of plate tectonics,” said Michael West, a seismologist in Alaska.
The 1964 earthquake caused severe damage to the state of Alaska, USA.
Earthquake History
In addition to the issue of plate tectonics, scientists also discovered the history of earthquakes in Alaska. Coastal forests in areas that suddenly subsided were inundated by seawater.
As field scientists dug deeper into the mud in these forests, they found layers of buried vegetation interspersed with ocean sediments. This indicates that the areas that subsided in 1964 had previously experienced multiple subsidence events during significant earthquakes spanning thousands of years.
Forests grew. Earthquakes occurred, the forests were submerged and covered by ocean sediments. Then the forests grew again.
By coring sediments deep in these forests and using new techniques to date layers of organic material within, scientists uncovered evidence of earthquakes that occurred thousands of years ago. Thus, the field of paleoseismology was born.
When they applied this method in the Pacific Northwest, they discovered the Cascadia subduction zone off the West Coast of the United States had previously caused significant earthquakes. This region is expected to experience future earthquakes.
Paleoseismology laid the groundwork for the U.S. Geological Survey’s National Earthquake Hazard Maps. These maps include estimates of the probability of earthquakes occurring across the country. Governments and companies rely on these maps to determine safe construction locations, the types of structures to build, and insurance costs.
The events in Alaska also helped scientists better understand the impact of landslide tsunamis during earthquakes, allowing them to monitor tsunami risks. Additionally, scientists warned that tsunamis could carry pathogens inland. However, no one could have anticipated this to develop preventive measures.
