Record-breaking survey investigates Alaskan ocean trench

By Alice Kim

A University of Hawaiʻi at Mānoa postdoctoral fellow took part in a world record for the deepest controlled-source electromagnetic (CSEM) survey of the seafloor. At 5,150 meters (approximately 3.2 miles) below sea level, the record-breaking survey happened above an oceanic trench in the Aleutian-Alaska Subduction Zone (AASZ) on June 6, 2019, during the research crew’s night shift. 

Postdoctoral fellow Dr. Eric Attias is participating as a volunteer crew member for the Electromagnetic Alaskan Geoprisms Experiment (EMAGE). This Columbia University project lead by Principal Investigator Dr. Kerry Key is using cutting-edge technology to survey the sea floor of AASZ. 

According to Key, Attias is helping EMAGE by using his experience working with the instrumentation used during the survey and his knowledge of electromagnetic data analysis and modeling to conduct quality control among other essential duties. 

“Eric’s experience … made my life easier since he’s taken on many of the duties I would normally be doing, which means I have more time to concentrate on overseeing the project,” Key explains.

“I was fortunate enough to participate in the EMAGE cruise thanks to my long-lasting collaboration with the Scripps and Lamont EM groups,” Attias says. “The EMAGE project utilizes state-of-the-art and unique EM system that was developed by the Scripps Institution of Oceanography EM lab, where only a handful of people worldwide know how to operate. This EM technology helps us to image both the shallow and deep Earth innovatively, while we study the fluid distribution in the crust and upper-mantle rather than structural geology, enabling us to understand the mechanism of the AASZ subduction zone and associated earthquakes.”

CSEM detects formations on the seafloor by transmitting an electromagnetic field through the seafloor and measuring the resistivity of the formations. EMAGE is using CSEM technology to study the fluid content of the crust and mantle along the Semidi and Shumagin sections of the Aleutian Trench, south of the Alaska Peninsula. The Semidi section lies south of the Shumagin Islands and Chirikof Island, and the Shumagin section lies south of the Shumagin Islands. 

AASZ is one of the most seismically active subduction zones in the world, stretching from the Gulf of Alaska to the Kamchatka Peninsula in the Russian Far East. A subduction zone is an area on the Earth’s crust where tectonic plates collide, and this collision creates volcanoes and causes earthquakes and tsunamis. The AASZ has experienced four earthquakes greater than magnitude 8 in the past seventy-five years, and one of them caused the 1946 tsunami that killed 173 people in Hilo, Hawaiʻi (also known as the “April Fool’s Tsunami”). 

As Key explains, EMAGE is studying how the transport and release of water along the plate boundary may regulate earthquake behavior and plate slip. EMAGE is looking for water trapped along fault planes on the incoming Pacific ocean plate, which is subducted beneath the North American plate. As the Pacific Plate slides beneath that North American plate, it can generate earthquakes (for example, the 1964 magnitude 9 Kodiak Island earthquake). EMAGE is hoping to map where the water exists and analyze the fluid content to explain why one part of the plate interface is locked and another region is freely sliding. The locked part may be storing up stress, which can suddenly release in a large earthquake. This earthquake can generate a large tsunami if the seafloor moves up and down enough or a submarine landslide is triggered.  

During the record-breaking survey, the ship was off the Alaska Peninsula, to the south of Kodiak Island. Key describes the scene that occurred around 1 a.m. as surreal with the darkness outside of the Research Vessel Sikuliaq’s Science Control Room lit only by a dim red light to maintain night vision. 

According to Key, the deep depths of this record-breaking survey allowed the researchers to study the geology of AASZ. The deepest deep-towed electromagnetic survey of a subduction zone ever made, EMAGE is only the third of this survey type; the first two were done offshore of Nicaragua and New Zealand. 

A week before the team reached the record-breaking depth of 5,150 meters, the team broke the world record for the first time at 5,100 meters (approximately 3.1 miles) below sea level, making the EMAGE crew two-time world record breakers during this survey.  

EMAGE is a research project by the Electromagnetic Geophysics Laboratory at the Lamont-Doherty Earth Observatory, Columbia University. 

Attias is a postdoctoral fellow for ʻIke Wai, a large-scale, multidisciplinary project funded by the National Science Foundation’s Established Program to Stimulate Competitive Research (EPSCoR). For ʻIke Wai, Attias is using the CSEM technology to survey how freshwater from the Hualālai aquifer, Hawaiʻi Island, releases into the ocean from below the seafloor.