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The National Science Foundation is funding the largest marine seismic-monitoring effort yet along the Alaska Peninsula, a region with frequent and diverse earthquake and volcanic activity. Involving aircraft and ships, the new Alaska Amphibious Community Seismic Experiment will be led by Cornell University in Ithaca, New York, with partners at the University of Washington and seven other research institutions.
“This effort will really change the information we have at our disposal for understanding the seismic properties of subduction zones,” said Emily Roland, a UW assistant professor of oceanography and one of nine principal investigators on the project.
The experiment will place seismic instruments on and off a 435-mile stretch of coast that includes the communities of Kodiak, King Salmon and Sand Point. The instruments will be deployed starting next spring and will record for 15 months, spanning two summer seasons.
“Most of what we know about subduction zones comes from land — we have instrumentation on land and we look out toward the ocean,” Roland said. “But there are big questions that are difficult to address unless you have observational capabilities right on top of the fault.”
Some 80 seafloor seismometers will be dropped as far as 300 miles offshore, with 25 having protection from trawling gear to allow them to operate in shallow water. The seafloor study area will cross the Aleutian Trench, the exact location where the Pacific and North American tectonic plates collide.
About 30 land-based seismometers will be placed simultaneously on the peninsula and nearby islands. Land-based instruments will supplement existing seismic instruments in the national Transportable Array and the Alaska Volcano Observatory.
A previous experiment, the Cascadia Initiative, deployed many of the same seismometers on land and at sea off Northern California and the Pacific Northwest between 2011 and 2015. The new experiment was modeled on that effort, and the two datasets will be complementary.
“We can think of this as being a similar plate boundary to the Cascadia Subduction Zone, but in many ways it behaves very differently,” Roland said. Those contrasts could reveal insights that can be applied to all subduction zone faults, she said.
The instruments are scheduled to go out next spring, with the first data to be recovered in the summer of 2019.
“This is something I’ve wanted to see done for a long, long time,” said lead investigator Geoff Abers at Cornell. “I’ve been working off the Alaskan Peninsula since 1990, and it became obvious that the only way to get something of this scale to work is in this kind of collaborative mode.”
The Alaska Subduction Zone, where the Pacific plate plunges below the North American plate, is the same type of coastal fault that threatens Seattle. Alaska is both the most active and the most volatile of U.S. faults: Ninety percent of all U.S. earthquakes occur here, and it’s the only U.S. fault that regularly unleashes magnitude 8 and 9 earthquakes. Most of the continent’s known volcanic eruptions occur along the Aleutian Island chain that lies north of the fault.
But despite being such a geologically active area, the remote region hasn’t been monitored very well — especially at the ocean bottom.
Recent improvements to seismic technology and reliability are providing an opportunity to do so. Precise recordings of how seismic waves travel through different places can pinpoint the makeup of the plates.
“We’ll be using signals from earthquakes we record to try and learn more about what the stuff down there is made out of,” Abers said. “Where do the magmas that show up in volcanoes come from? Somewhere below the crust they form, and there’s a lot of debate about what that process is. And how does that actually trigger the volcanos, and why are they where they are?”
Researchers also hope to understand why the westernmost portion of the study area, near the Shumagin Islands, is the only section that has not recorded a major earthquake for decades.
“We think, based on land observations, that the underlying plate is just constantly moving along and relieving stress, and we don’t expect it to generate a large earthquake in the near future,” Roland said.
The eastern part of the study area, near Alaska, has generated magnitude 8 and 9 earthquakes within the past century. Geologists believe that section of the fault may be locked, building up stress in the same way as the eerily quiet Cascadia Subduction Zone, she said.
“So that makes this a very interesting place to observe both micro-seismicity, which might allow us to understand how stress is relieved, and ways fault structure influences earthquake behavior,” Roland said.
In preparation for the experiment, the team has mapped the best drop location for each seafloor seismometer and is now coordinating a deployment schedule with a fleet of research ships. The team worked with Alaskan landowners, educators and pilots to negotiate land-based locations. Beginning in 2019, data will be provided openly to the entire science community through the Seattle-based IRIS Data Management Center.
“There’s a lot of excitement and anticipation for the data,” Abers said.
The project is funded by a $1.5 million grant from the National Science Foundation, with approximately $3 million more in costs covered by partner organizations. Other participating institutions are the University of California, Santa Cruz; the University of Colorado; Columbia University in New York City; Washington University in St. Louis; the University of New Mexico in Albuquerque; Colgate University in New York state; and the U.S. Geological Survey. Ocean-bottom seismometers are provided by the Woods Hole Oceanographic Institution and Columbia University’s Lamont-Doherty Earth Observatory.
Source: University of Washington