The first SEAMSTRESS experiment successfully started this summer (July 2019) and will continue next summer. The experiment is conducted in close collaboration with Geomar (in Kiel) and Awi (Bremerhaven). The first part of the experiment was done using R/V Helmer Hanssen in an expedition lead by professor Stefan Bünz from UiT. The scientific crew comprised ten fellows (including PhD students, researchers and technicians) from UiT and GEOMAR and two intern students from India.
One part of the experiment consisted on recording acoustic waves that can give us a tomography (sort of radiography but with lower frequencies) of the rocks beneath the ocean. Having a tomography is like seeing through the ground. Waves generated from an air gun towed behind the ship travel through the water column, then through sediments and back up to be recorded by a seismometer that sits on the seafloor. The waves tell us whether there are cracks, or if there is gas or frozen gas (hydrates) accumulated. During this expedition, we placed 22 ocean bottom seismometers (OBSs) on the seafloor (just by dropping them into the water with a weight attached to it) for what we call the “active seismic experiment” (we generate the signal ourselves with the air gun). The instruments were collected by the end of the cruise that lasted about a week.
The second part of the experiment is still ongoing. It consists on recording acoustic waves generated by the Earth itself. We left 7 OBS instruments on the seafloor for what we call the “passive seismic experiment”. We will collect these instruments next summer by sending an acoustic signal from the ship to release the weight that keeps instruments on the seafloor. Passive seismic experiments involve energy generated by earthquakes and other ambient sources (it is also possible to hear the whales). Our ultimate goal is to develop a regional stress model using seismic records of this dataset. If the same tremor or wave is recorded by several OBS instruments we can predict where it came from and what caused it (movements along faults, movement of fluids through cracks, etc).
We will repeat this experiment in 2021 in another area to get a better idea of what kind of stresses are affecting the release of methane to the ocean in the area.
Text: Sunny Singhroha and Andreia Plaza-Faverola
Pictures: Stefan Bünz