Once upon a time there was a little mermaid, with the upper body of a human and a tail of a fish, happily diving within the seven seas. Wait … I’m sorry, that is the wrong story. I will tell you today something about a different generation of MERMAIDs, that are pretty useful for seismologists. It is a very exciting story indeed.
Over the last decades seismic station coverage dramatically increased worldwide, which improved 3-D models of the Earth’s interior. However, the data coverage is still geographically unequal since especially seismic monitoring in marine areas is limited. This lack of seismic data affects the possibility to image the interior of the Earth.
“Thus, all 3-D Earth models are marked by blank spots in areas […] where little or no information can be obtained.” Simons et al. (2006)
What is MERMAID and how can it improve the imaging of the Earth’s interior?
MERMAID is an acronym for Mobile Earthquake Recording in Marine Areas by Independent Divers and it consist of hydrophones that record water pressure variations induced by P-waves. MERMAID is quite smart and can distinguish for example between an earthquake and whale singing, so that only significant signals are recorded. The data transmission in near-real time is a huge advantage over Ocean Bottom Seismometers (OBS).
There are two generations of mermaids: The ‘original’ MERMAID, brainchild of Guust Nolet at Geoazur in France, drifts passively and surfaces only after recording a P-wave that it classifies as an Earthquake. A new, recently deployed instrument called Son-O-Mermaid operates at a water depth of about 1500 meters, while a drifting buoy stays at the surfaces and allows the continuous contact with a satellite.
“The MERMAID drifts passively […] until an earthquake signal is detected. If this is identified as a strong P wave, the MERMAID ascends for transmission of the recorded waveform as well as its global positioning system (GPS) coordinates at the surface.” Sukhovich et al. (2015)
Of course the ambient noise in the oceans can be high, but it is a huge success that MERMAID can record up to 60% of distant earthquakes. Up to now, MERMAIDs have a battery lifetime of about 2 years and the next generation will have already a lifetime of 6-8 years which will give them enough time to happily float around and record a lot of earthquakes.
The above short video about the MERMAID project shows actual footage of the recent deployment of Son-O-Mermaid near the Bermudas!
“The Future of Oceanic Data Collection
A worldwide array of MERMAID floating hydrophones, on the scale of the current international land-based seismic arrays, has the potential to progressively eliminate the discrepancies in spatial coverage resulting in poorly resolved seismic Earth models.” Simons et al. (2006)
If you want to know more about MERMAID and I think you definitely want to, then have a look at these websites:
- The MERMAID Project | The Son-O-Mermaid (http://geoweb.princeton.edu/people/simons/MERMAID.html)
- MERMAID (Mobile Earthquake Recording in Marine Areas) (https://www.geoazur.fr/GLOBALSEIS/sukhovich/File1.html)
- The Son-O-Mermaid: A Green Platform for the Blue Ocean (http://geoweb.princeton.edu/people/simons/Son-O-Mermaid.html)
- Access to Mermaid Data (https://www.geoazur.fr/GLOBALSEIS/Data.html)
- Catching a (seismic) wave: Simons measures earthquake in the oceans (http://www.princeton.edu/main/news/archive/S46/59/17Q06/)
Sukhovich et al. (2015): Seismic monitoring in the oceans by autonomous floats, Nature Communications 6:8027 (http://www.nature.com/articles/ncomms9027)
Simons et al. (2006): A Future for Drifting Seismic Networks, EOS, Vol. 87, 31 (http://www.princeton.edu/geosciences/people/simons/pdf/EOS-2006a.pdf)