One Year Later – Return to the NoMelt Site
The R/V Marcus G. Langseth completed the initial portion of the NoMelt experiment on Dec 29, 2011. In the subsequent year, scientists began analyzing the active-source seismic data collected on that cruise, constructing initial models of the oceanic plate. The full analysis awaits the so-called “passive source” data – the year-long recordings of earthquakes and natural electrical and magnetic signals on the instruments that remain on the seafloor.
On Dec. 18, 2012, the R/V Melville departed San Diego to recover remainder of the NoMelt instruments and data. The expedition includes two scientists from Columbia’s Lamont-Doherty Earth Observatory: Post-doctoral scientist Patty Lin and graduate student Natalie Accardo. Natalie is sending regular reports from the ship, and I will post them here.
Post 1: Natalie Accardo, Dec. 19, 2012.
In the early hours of Dec. 18, a team of scientists aboard R/V Melville set out from San Diego to a remote portion of the Pacific Ocean on a trip that will take 28 days and cover more than 8,500 kilometers. On this voyage, we aim to recover 27 ocean bottom seismographs (OBS) instruments that have been sitting silently on the ocean floor for nearly a year. Throughout their stay on the seafloor, the OBS have been continuously listening and recording the shaking caused by distant earthquakes all over the world. By recording ground motion, we can constrain seismic wave properties and in turn the geologic characteristics of the oceanic plate. With this information, we hope to answer the multilayered question of what defines a tectonic plate.
For decades, geologists have focused most of their attention on locations where tectonic plates come together (i.e. subduction zones like Japan) and break apart (i.e. rift settings like the East African Rift System). Yet to better understand the complex processes happening at those sites, we must first understand the fundamental characteristics of a tectonic plate. For further information concerning instrument deployment and other aspects of this project, please refer to previous blog entries.
It takes seven days to make the 4,300 km journey from San Diego to the NoMelt OBS sites. During the transit time, we use instruments aboard the Melville to map topography and gravity of the ocean floor. Additionally, at regular intervals we toss “drifter” instruments overboard. These so-call “instruments of opportunity” were designed by students at the University of California San Diego (UCSD) to be deployed by any research vessel traveling through an area of interest. They are completely autonomous and will record sea surface information (temperature, salinity, etc.) wherever the currents take them, data that will be of use to oceanographers at UCSD.
Today marks only our second day on board and has given us our first true glimpse of the open ocean. Rocky seas have confined most of the science party to their bunks in a group effort to retain what is left of our last meal. However, the promise of calmer weather in the coming days has brought some cheer to the entire crew.