Most of the major natural hazards associated with geological activity, including major earthquakes, volcanic eruptions and tsunamis, occur when the rigid tectonic plates of the lithosphere or outer layer of the planet collide. Beneath the plates is the asthenosphere, a 200-mile-thick layer of Earth’s upper mantle made of very hot material, part solid rock and part viscous magma, which lubricates the movement of the plates. Since the discovery of plate tectonics 50 years ago, scientists have made significant progress in understanding these processes, but there are still many unknowns about this hugely complex system, especially how the features of the asthenosphere contribute to seismic and volcanic events.
Teacher James Gaherty and associate professor Ryan Porter from Northern Arizona University School of Earth and Sustainability recently received $473,000 from the National Science Foundation for a study of the Cocos Ocean Plate beneath Central America. NAU is collaborating on a large project led by Samer Naif of the Georgia Institute of Technology. Gaherty and Porter will lead the seismological portions of the expedition, while Naif will lead an electromagnetic imaging effort. The NAU team, made up of graduate students and early-career scientists, will participate in two research expeditions to the Pacific Ocean over the next four years to study the region’s tectonic and geodynamic processes that control faulting, magmatism, surface deformation and their associated human effects. repercussions.
The team will use unique seafloor sensors to collect seismic signal data and report it to NAU’s Geophysics Lab, where graduate and undergraduate students will gain research experience analyzing the data. The resulting seismic images of the Cocos plate and the underlying asthenosphere will be integrated with complementary electromagnetic images constructed by Naif and his team.
“Much of Earth science research focuses on ongoing processes – examining why an earthquake starts and stops where and when it happens, for example, or exactly how magma rises from tiny melt pockets deep in the mantle and accumulate in a magma chamber just below the surface,” Gaherty said.
However, to understand these processes at any given location, one still needs to better understand the larger system, including the forces driving the plates, the types of rocks involved, the conditions that cause those rocks to break – forming faults and earthquakes – and conditions. under which they sink like Silly Putty or melt, potentially forming volcanoes.
He noted that the asthenosphere plays a huge role in controlling plate motion and providing the source of melt for most volcanism, and by better understanding the weakness of the asthenosphere and the amount of melt it produces. , scientists can better understand the processes underlying volcanism. the activity and movement of the plates that lead to earthquakes.
Using a fleet of ocean floor seismometers (OBS) and ocean floor electromagnetometers (OBEM), the team will focus on seafloor data in an area off the west coast of the Central America, through a feature called the Nicaraguan Fracture Zone (NFZ). The water in this region ranges from 3,000 to 4,500 meters (9,800 to 14,700 ft) in depth. The OBS and OBEM will operate autonomously on the seabed, recording natural seismic and electromagnetic signals for approximately one year.
“Using passive-source seismic and electromagnetic imaging to quantify the shear rate and electrical resistivity of the lithosphere and asthenosphere on both sides of the NFZ, the team will address a number of key questions associated with the state of the asthenosphere and the nature of intraplate volcanism near the meeting of the Cocos, Nazca and Pacific plates, Gaherty said.
Ultimately, the team hopes to provide a new understanding of how much melt exists in the asthenosphere and the role it plays in volcanic processes and plate mobility.
Gaherty, who joined NAU in 2020, has worked on several other projects that use similar approaches in other parts of the Pacific, but this is his first time working in this region. To learn more about Gaherty’s previous expeditions, visit this research Blog with entries written by several scientists and students.
“I love having the opportunity to collect data that samples parts of the Earth that have never been photographed in any other way,” Gaherty said. “Seismic networks are historically restricted to land and in many cases to highly developed regions. Over my career I have had the opportunity to probe a wide range of tectonic systems that have never been explored before. using these types of seismic techniques, including remote locations in the Northwest Territories of Canada, islands at the eastern tip of Papua New Guinea and deep in Lake Malawi in South Africa. The expanses of the ocean basins are particularly special, and this will be the fifth seismic survey in the Pacific that I have conducted. The data has led me, my students and colleagues, to a much better understanding of the processes at the origin of plate evolution. They also live on as unique data for a wide range of other researchers to mine. NASA emphasizes the excitement of exploring new planets; I take great satisfaction in exploring the depths of Earth’s ocean basins in a way that has never been done before.
The team will work with international partners to share data, improve understanding
The team will work directly with international partners in the region who represent national earthquake monitoring networks in El Salvador, Nicaragua and Costa Rica. Representatives from each organization will be invited to join both expeditions, gaining unique training and experience in oceanographic data collection and ocean floor geophysical instrumentation and enabling a host of scientific analyzes that will enhance understanding of seismic hazards. and tsunamis in the region.
Kerry Bennet | University Marketing