Thursday, April 12, 2012

Travel time

Here we are only four days away from Honolulu, after some 2 weeks and a half at sea. This is my fourth cruise and it will be the longest one so far. And the first leg of the Shatsky Rise cruise lasted for 60 days! But, exactly how long will this second leg take? That is, with all the date and time changes, what will the real duration of the cruise be? We sailed off at around 8 am on March 24th and will dock at approximately 8 am on April 15th, which gives 22 days. We had one day change in which we went back in time and repeated April 8th, so it's 23 days. Finally, when we get to Honolulu we will have made four hour changes of +1 hour, which means that we need to subtract 4 hours from the real time duration. Then my final approximate guess is 22 days and 20 hours. Is this correct?

Last day I posted was April Fools' Day, today is Cruise Picture Day. At 1 pm this afternoon, we all gathered in the muster deck, just behind the bridge, and arranged the picnic tables so that the people in the front could sit and the people in the back could prove that they had been in the cruise too. This may sound corny, but this is probably the best souvenir I will be taking home. Unfortunately, for the moment I can only tell you the story because the pictures are not uploaded yet, but I'm sure we will get to see at least one of them in one of the following posts.

But this is a science cruise, so I guess I'm supposed to have some science content in my posts. In the previous one I told you about my thesis main topic: travel-time tomography which is used to model wide-angle seismic (WAS) data. In this second leg of the Shatsky Rise cruise only MCS data have been acquired, so maybe some of you don't know exactly what WAS data is about. In the first leg of the cruise though, there were a couple of WAS data profile and if you check the older posts you will find all you need to know on the acquisition of this kind of seismic data. But once collected, what do we do with these data? That is precisely the purpose of tomo2d and tomo3d. From WAS data we obtain the time interval of seismic waves traveling from source to receiver: the observed travel times. From these, we want to recover a velocity model for the Earth subsurface. Briefly, what the two TTT codes do is simulate the source-to-receiver rays, calculate synthetic travel times for them, then compare these with the observed ones, and finally translate these differences in travel time, or travel-time residuals, to changes in the velocity model. This process is repeated until the resulting velocity model produces synthetic travel times that fit our data to a desired level of accuracy.

As you will know, Team Awesome is also Team Multilingual, and we have had time to learn some French, Chinese, Spanish and of course English. As this likely to be my last post, I'm going to leave you with a multiple choice question to improve your Spanish. The question is based on an anecdote that I'm glad didn't happen to me (you can ask me about it), and I think it will be useful if you ever get a cold while staying in Spain, although English takes you almost anywhere these days: What is the Spanish translation for “I have a cold”? (a) “Estoy constipado”, (b) “Tengo frío”, (c) “Estoy resfriado”, (d) Both (a) and (c) are correct, and (e) “Tengo un frío”. I realize that 5 possible answers is probably too many, so here is a hint, the literal translation of “I have a cold” is a wrong answer.

Oh, I almost forgot! In my first post I said I would tell you about the “First and Second Last Names Paradox”, from now on FSLNP. The FSLNP arises from the fact that in Spain newborns are given a last name from their father and another one from their mother. The tradition is that the first last name of your father be your first last name and the first last name of your mother, your second last name. But nowadays you can have that the other way around too. A funny consequence of the FSLNP is that when we travel to the US, our first last name is assumed to be our middle name and our second last name is picked as our last name. That is basically what happened here on the Langseth, where I've become Adrià M. Catalán.

1 comment:

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