Return to the Alaska Wilderness
USGS Scientists explore one of North America’s fastest-moving faults
Five geologists spent two weeks in the Alaskan wilderness studying one of the fastest-moving earthquake faults in North America. Project leader Rob Witter led the team on the expedition to the Fairweather Fault, only accessible by boat, with the group camping outdoors during their field work.
Even though their work takes place 500 miles from the contiguous U.S., much of what the team will learn during the ongoing project can be utilized in many other areas.
“Our research in Alaska likely will have its greatest impact elsewhere in the U.S., by informing federal agencies and the public about the seismic hazards posed by the Fairweather Fault,” said Witter. “Our data will be used to update the Alaska seismic hazard map, part of the collection of USGS maps used to support effective building codes. Other federal agencies, such as the National Park Service, NOAA, U.S. Forest Service, and FEMA use our data to increase public safety related to earthquake and tsunami hazards.”
The team hopes to also determine how fast the tectonic plates on each side of the fault slide past each other and how this fault “slip” has altered the landscape at Icy Point. The rate (or speed) that a fault slips controls the time between earthquakes, and is a critical input for seismic hazard assessments in a region.
In 1958, a magnitude 7.7 earthquake struck Lituya Bay, Alaska — leading to a tsunami that devastated the area. The earthquake was studied right after it occurred by USGS geologist Don Miller and University of California, Berkeley geologist Don Tocher. Last year, Witter and his team picked up the trail to use new technologies to understand the Fairweather Fault’s motion.
Witter’s work leverages research done by USGS geologist George Plafker, who worked along the Fairweather Fault in the 1970s.
“We continue to consult these scientists to take advantage of legacy data they contribute, including field observations, aerial photography, and radiocarbon dates on glacial moraines and marine terraces,” Witter said. “Their many years of experience working in the region can help our team target the right research questions and be better prepared for what we might find in the field.”
This year, Witter’s field team included USGS geologists Adrian Bender, Richard Lease, Kate Scharer, and Humboldt State University geologist Harvey Kelsey.
Field Work Advances Science Research
Despite huge advancements in remote sensing (e.g., satellite) technology, there is still a need for scientists to physically look at, study, and collect samples from the Earth’s surface in order to decipher its history.
For example, during their fieldwork, the team discovered that the valley east of Icy Point had been impacted by both glaciers and faulting in the geologic past. They discovered the valley once had been filled by a lake. The field crew collected samples of trees buried by gravel from glacial outwash streams, and radiocarbon dating will determine when the trees died. They also found bivalve shells on a terrace lifted 30 feet above today’s sea level, from which they will determine the age and rate of that uplift. The team will use the age and elevation of the deposits above sea level to understand how fast the landscape has been lifted up or down by large earthquakes.
All these field observations and samples can only be collected by scientists with “boots on the ground.”
“Geologists have to go into the field to collect data,” said San Andreas Fault-expert Dr. Kate Scharer. “Though satellite images are important, we cannot collect samples of the past landscapes from behind our desk. We will take our observations back to the lab and the computer, but for this type of work, there is no other method but to start in the field.”
Scharer describes Icy Point as a beautiful yet complicated place with a geological history spanning many thousands of years. The diverse terrain, with a deep-rooted history, requires more than the physical ability to endure the strenuous work needed to explore this remote area.
“In an early edition of the Boy Scout Merit Badge pamphlet for Geology, there is a phrase about how geologists wear their 'mental boots.' I have always loved this, because it is our job to be out there, to make clear observations, and to recreate the past from what we can see on the ground and analyze in the lab.” Scharer said. “This takes careful thought, but also a lot of walking around! Certainly the most challenging and rewarding aspect of this science is to keep developing hypotheses and then building on them or discarding them, depending on the data collected from our field work. It takes mental boots!”
Read about the team’s previous work in Alaska: Uncharted: Exploring one of America’s fastest faults