Mrs Mermaid (by sarah)
Mobile Earthquake Recording in Marine Areas by Independent Divers
This was last week it was the second one of the Departmental Research semiars which UCL's Earth Sciences department are having. This turned out to be about the project I had heard about when doing the MRes before becuase back in those days Frederik Simons was at UCL and thus took some of the Birkbeck classes - he's now at Princeton. I remembered his stuff from before so well as it involved fourier transforms which at the time Alaric was having issues in using himself. It was intersting to see how the project had evolved and to also to here yet agian the run down on the gaps in our knowledge of the earths structure due to the uneven distrabution of earthquake detectors - ie on land!
The interesting things I picked out of this talk was that the presance of mantle plumes below certian volcanics - ie the stuff that occures in the middle of the oceans away from either subduction zones or mid ocean rifts. I hadn't realised this and thought it was all sorted out!
In fact it turns out we are still asking questions like:
What is the convection style of the mantle
What is the nature of mantle plumes and what is the heat flow like
Then another interesting thing is are the siesmic data consistant with mineral physics.
Again Tomography came into it and he showed some really groovey pictures of like the who earth though there are lots of gaps still!
It also turns out that not only do you have to deal with the fact that the earthquakes are not evenly distributed but that they are often of the wronge size - now it's obvious that the majority of quakes will be too small to get any useful data out but what I hadn't appreciated was that they can also be too big! They fail as they are too big to actually be used as a point source!
He ran through things like Argo which have floating devices but these are tethered and there fore pick up alot of noise and stuff. If they get the funding for their floatation devices it seems that we would get much better data.
I remembered that there was a low velociety channel in the oceans but I hadn't known that the whales use it as obviosly the sound waves travel further. This can cuase problems as there are sound waves that can initially look like the p-waves from earthquakes - you seem to need to put the data through a few processes and then they look different this is important as it turns out you can use the initial 2 seconds of p-wave to predict the size/magnitude of the earthquake - p-waves are the first ones to arrive but they are what are known as body waves and they dont do any damage it is the surface waves that lag behind them that destroy buildings and if there is going to be a Tidal wave then there is even more warning for that.
This is still a highly contested idea but it would be cool if it worked - Japan seems to be the most lickly place to find out!
I went to the drinks afterwards but didn't get a chance to actually ask my questions about what type of batteries they are using on the devices as they look like one of the main issues - I also wanted to ask about how the positioning system worked but never mind.
Tue 21st Oct 2008 4:06 pm 
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By Frederik Simons, Tue 24th Mar 2009 @ 2:26 pm
Hi Sarah,
I found your post by accident. We are using Lithium batteries for the first Mermaid, and the positioning is by the crude Argos satellite system. However, in the new Mermaid, we will be using GPS. In the latest incarnation of the instrument, the planned Son-o-Mermaid, we will be using traditional Alkaline batteries as a back-up to a green-energy wave-action generator - i.e. the instrument itself will be generating energy as part of it will be bopping around in the waves up and down from the submerged part that contains the hydrophones...
By Sarah, Fri 27th Mar 2009 @ 10:48 am
Cool thankyou 🙂