Report to the UO Department of Geological Sciences from Santorini: “Marine Geophysics in Action”
by Emilie Hooft (Chief Scientist), Dec. 4th 2015, from the R/V Marcus Langseth
We are ¾ of the way through a 4-week-long seismic expedition to the volcanic island of Santorini, the source of Earth’s largest super-eruption in the past 10,000 years. I am sitting in the large “main lab” of the US Research Vessel Marcus Langseth, deep below the main deck and surrounded by an impressive bank of monitors. The computers reflect the vast quantities of data we are collecting: the generation of the seismic sound source, multibeam bathymetry and backscatter, sub-bottom profiling, gravity, magnetics, navigation, weather, and sea state.
The resources of the most sophisticated seismic ship in the academic world have come to the Aegean. The goal is to understand the deep roots, or magma plumbing system, of an arc volcano. We have some idea of how shallow magma bodies are shaped, but the magmatic system that lies in the deep crust beneath remains poorly understood and difficult to study. It is in this region that magmas from the mantle undergo chemical processes to form the rock compositions that presumably dominate the continental lower crust.
Santorini, besides being an idyllic vacation spot, is perfect for tackling this problem. It recently experienced significant unrest due to magma recharge, including inflation of the ground and intense earthquake swarms during 2011-2012. Since Santorini is a semi-submerged volcanic system, we can use the R/V Langseth to collect a large and very dense 3D marine-land seismic dataset; collecting a similar quality data set for an onshore volcano, such as those in the Pacific Northwest, is not possible. At the start of the expedition we dropped 91 specially designed seismometers to the seafloor to record the seismic sound source. My British and Greek colleagues have installed another 65 land seismometers on Santorini and nearby islands. The R/V Langseth will shoot her guns over 12,000 times to achieve the desired outcome, which is to sample the seismic wavefield with unusually high spatial density.
Once back on shore, we will apply state-of-the-art travel time and waveform inversion methods to the seismic data; methods that promise to reveal the structure of the entire crustal magmatic system and its surroundings in 10 times more detail than at any volcano to date. A primary goal is to define the magma geometry and connections throughout the crust – physical parameters that control magma migration, storage, and eruption are also important to predict eruptive potential.
During our transits back and forth around the volcano we are mapping regions of the seafloor that have never been observed in detail before. The structure of faults and landslides between the islands of Santorini and Amorgos reveal themselves daily. These measurements will help resolve the enigmatic occurrence of the largest 20th century earthquake in Greece (1956, M 7.5) and its accompanying tsunami. This looks to be one of many secondary products from this study.
This is a large team effort and several colleagues have amplified the project. Prof. Joanna Morgan (Imperial College London) took DoGS graduate student Joe Byrnes to install seismometers on beautiful Anafi, while her colleague and husband Prof. Mike Warner worked with several teams on Santorini itself. To install stations on the islets of Anhydros and Christiana, Prof. Costas Papazachos (University of Thessaloniki) even managed to organize a military helicopter.
The shipboard science party includes 8 members from our own department: Profs. Emilie Hooft (Chief Scientist) and Doug Toomey (co-Chief Scientist and GoPro expert); graduate students, Gillean Arnoux, Brandon VanderBeek, Miles Bodmer, Ben Heath, and Dan O’Hara; and undergraduate Claire Getz. Greek co-Chief Scientist, Prof. Paraskevi Nomikou (University of Athens), helps us navigate Greek waters and the party is complete with one British and two Greek graduate students. The students help with design and planning, work with the technicians putting instruments on and off the ship, and monitor, document, and process all the different data streams. They are now experienced shipmates and mix well with the range of characters that crew the vessel. An incredible experience!