DVIDS – News – An NRL scientist in the right place, at the right time to record a historic earthquake
WASHINGTON – Ben Phrampus, a researcher at the United States Naval Research Laboratory (NRL), recorded the largest earthquake in the United States in nearly half a century when he recently struck off the coast of southern Alaska. The magnitude 8.2 earthquake went almost unnoticed as it was nearly 20 miles below the ocean floor. However, it briefly triggered evacuations, tsunami warnings in the area, and two aftershocks of 6.2 and 5.6, respectively.
Phrampus, a physics researcher in the geology and geophysics section of the NRL, was in the right place at the right time while on watch aboard a research vessel when the earthquake struck on July 29, and the instruments of the crew recorded the event.
The US Academic Community National Seismic Research Center, Marcus G. Langseth, operated by the Lamont-Doherty Land Observatory Marine Operations Office at Columbia University, was located west of a chain of islands called Haida Gwaii, off the North Pacific coast of Canada. An acoustic receiver, known as a hydrophone streamer, recorded the noise while in the water at the time and showed a massive spike.
“Seeing it live on the data stream was particularly exciting,” said Phrampus. “We were actually seeing the acoustic waves of the earthquake on our instruments in near real time, which is just great. “
The earthquake occurred near Perryville, Alaska, a small community on the Alaska Peninsula about 500 miles southwest of Anchorage.
“I was on guard (on duty) watching the incoming data to make sure everything looked okay,” said Phrampus. “There have been times when I looked at the streamer’s data at the right time to capture the event as it happened.”
The technicians on board were primarily concerned with what they saw.
“We wanted to be sure there was no problem with the equipment,” he said. “We quickly recognized that this was not an equipment problem. This led to our curiosity to find the source.
A quick check revealed it was an earthquake. They confirmed their findings after checking the website of the US Geological Survey, which reported the magnitude 8.2 quake.
After the tsunami warnings were triggered, residents of the coast rushed to higher ground and / or were evacuated. The earthquake was the strongest in North America since a 9.2 magnitude earthquake in Alaska in 1964. Known as the “Great Alaskan Earthquake,” it spread through the center South Alaska, cracks in the ground, collapsing structures and tsunamis. More than 130 people died in the strongest earthquake on record in North America. It is the second largest earthquake ever recorded on Earth.
The most recent earthquake may have caused light to moderate damage and moderate tremors, according to preliminary seismic data. The US National Tsunami Warning Center has canceled a tsunami warning issued for parts of Alaska after waves of less than one foot hit the coast. The tremors spread throughout the Alaska Peninsula and Kodiak.
Phrampus said an offshore break has spread to the seabed along the continental slope. This produced seismic energy that interacted with the Sound Fixing and Telemetry Channel, or SOFAR, which is an ocean channel that allows sound to transport great distances, according to the National Ocean Service. The ocean is made up of many areas, and sound can travel through an area for hundreds or even thousands of kilometers. Interaction with SOFAR converted energy into sound waves, a process called downslope conversion, said Phrampus.
This interaction trapped the acoustic waves in the water column and helped their propagation in the Pacific Ocean. Just 20 minutes later, the hydrophone streamer recorded the event, said Phrampus, surprising and exhilarating the crew.
The research team is assessing the tectonics and seismic risks of earthquakes and tsunamis along the Queen Charlotte Fault, which has produced large earthquakes in the past. While the recent event was exciting enough, there is still a lot to learn about the most recent earthquake and the fault itself, he said.
“We only did a preliminary scan to verify that the 8.2 earthquake is what we are seeing on our equipment,” he said. “We will be digging deeper into this area in the coming months. “
The research cruise ended on August 24. The results will be presented to the American Geophysical Union in New Orleans in December.
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