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NOAA maps tectonic faults

Daily News Staff Writer

Researchers from the National Oceanic and Atmospheric Administration, U.S. Geological Survey and their partners recently completed the first high-resolution, comprehensive mapping of one of the fastest moving underwater tectonic faults in the world, which just so happens to be partially located in Southeast Alaska. The data will help coastal communities prepare for risks from earthquakes and tsunamis.

The Queen Charlotte-Fairweather fault system is a 746-mile-long strike-slip fault line — a fault that moves side to side — that extends from offshore of Vancouver Island, Canada, to the Fairweather Range of Southeast Alaska.  

Although USGS has known about large earthquakes along the fault system, Peter Haeussler, a research geologist with USGS, explained that researchers didn’t have much in-depth data about the fault system.

Now scientists have a little more insight into the record-breaking fault system, thanks to the most recent survey on the NOAA research ship Fairweather.

From April through July, USGS scientists collected multibeam bathymetric data along the U.S. and Canadian international border in water depths ranging from 500 feet to more than 7,000 feet deep. Haeussler explained that multibeam bathymetric data gives an in-depth look at the sea bottom.

“It typically acquires data that is four times the width of the water depth, so if you’re in 100 …. feet of water, then you’ll get a swath of 400-feet wide showing you all the little bumps and stuff on the sea bottom as you go along,” Haeussler said. “It’s basically the state-of-the-art way that oceanographers use to map the sea bottom.”

Even with the new mapping advancements, scientists likely don’t know as much about the The Queen Charlotte-Fairweather fault as they do about its famed counterpart: The San Andreas fault in California. The two faults form the boundary between the North American and Pacific tectonic plates.

“It’s the same plate boundary, the same two plates moving past each other — but the big difference is that the San Andreas fault is mostly on land, whereas the Queen Charlotte fault system is entirely offshore and underwater,” the research geologist said.

Another difference between the two is their slip rates. The Queen Charlotte fault system has a slip rate of more than 2 inches per year, making it one of the most fast-moving strike-slip faults in the world. The San Andreas fault slips about an inch to an inch-and-a-half each year, according to USGS.

According to Haeussler, this matters because fast-moving faults more commonly create large earthquakes compared to slow-moving faults, which is apparent with the Queen Charlotte fault system. Movement between the tectonic plates at the fault line has generated six earthquakes of magnitude 7 or greater within the last century, according to USGS.

An article in Earth and Space Science News magazine states that the 2012 magnitude 7.8 Haida Gwaii earthquake, centered on Moresby Island, British Columbia; and the 2013 magnitude 7.5 earthquake near Craig increased awareness of the potential geologic hazards posed to residents of Southeast Alaska and western British Columbia.

Haeussler said earthquakes can shake the ground so much that they can cause underwater landslides, and other phenomena. It’s those kinds of things that can sometimes cause tsunamis, Haeussler explained.

Take, for example, the magnitude 7.8 earthquake in July of 1958, which the Fairweather fault is known for.

“It caused a big landslide which then hit the water, and then caused the world’s largest tsunami runup ever of 1,740 feet within Lituya Bay,” the research geologist explained.

Haeussler said the data USGS and NOAA have gathered through this mapping expedition gets incorporated into updates for the seismic hazard map for the State of Alaska, and is helpful to other entities as well, such as the Alaska Department of Fish and Game.

The research geologist said the seafloor mapping can help Fish and Game understand bottom-dwelling fish.

“It also enters into tsunami modeling,” Haeussler said, “and just having a better picture of what the earth is like.”

The 2018 Fairweather survey built on five previous USGS-led marine geophysical and geological surveys between 2015 and 2017 in Southeast Alaska aboard a number of research vessels, as well as two cruises led by researchers from the Geological Survey of Canada, Sitka Sound Science Center and USGS, according to a press release.

The prepared statement from USGS and NOAA states that scientists have been gathering sonar data on the Queen Charlotte-Fairweather fault system since 2015 because of the two aforementioned large-magnitude earthquakes and associated aftershocks in 2012 and 2013.

The research cruises in 2015 were the first systematic effort to study the fault system in U.S. territory in more than three decades, and a similar effort led by the Geological Survey of Canada has been underway along the portion of the fault located in Canadian territory, the press release stated.

“Working with USGS and our state and academic partners allows us to speed the development of information that can help communities better anticipate and prepare for risks from tsunamis and earthquakes,” said W. Russell Callender, assistant NOAA administrator for the National Ocean Service, in a statement.