What are we doing out here?

The Aleutian arc is an active string of volcanoes formed over a subduction zone, where two of Earth’s tectonic plates collide and one is forced under the other. These geological settings create the largest and most destructive earthquakes and tsunamis and some of the most active volcanoes on the planet. While some of the magma generated at subduction zones erupts at arc volcanoes, a large portion of it crystallizes before reaching the surface, adding as much as 10-20 km to the crust, the outer layer of the Earth. Although subduction zones may be one of the most significant places where new continental mass is created, we still have many questions about the composition and thickness of this new material. The composition of lavas at the surface change dramatically between adjacent volcanoes – what is happening under the hood to create that variability?

The Aleutian subduction zone has also produced a series of very large earthquakes and tsunamis in the last century, including a magnitude 8.6 earthquake that occurred in our study area in 1957. Our imaging will provide new information on the source region of these earthquakes.

During this study, we will use sound waves to image the Aleutian subduction zone, with a focus on mapping the geology below the Aleutian volcanoes to determine the composition and thickness of the crust and how it varies along the arc under volcanoes with different lava compositions. Sound waves will be generated by a seismic sound source towed behind the ship, and returning sound waves will be recorded on ocean bottom seismometers deployed on the seafloor and a long cable filled with pressure sensors towed behind the ship; these are very sensitive instruments that can record weak returning sound waves from deep in the earth. Data will be collected on transects along and across the subduction zone. Additionally, we will be collecting a suite of other oceanographic and geophysical data throughout the cruise. We are excited about what we will learn – stay tuned!

Planned seismic study for September-October 2020 in the Aleutian Islands

Donna Shillington, NAU

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