Mid-term Colloquium by Andreas Rosing – Niels Bohr Institute - University of Copenhagen

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Mid-term Colloquium by Andreas Rosing

Title: Tomographic inversion of Lg-surface waves in Northern Europe.

My masters thesis is an inversion investigation of the underground around Denmark. For the inversion I use Lg-surfacewave, instead of P- or S-wave as it's normally done. There haven't been done a lot of Lg- investigations, so it's more interesting to see if this method proves valuable in comparison to other methods. An earlier thesis had a major constriction on the inversions because it used an available program, that nobody knew how worked. To avoid problems like that, and to get a programme that can be used by future investigations, if anyone will do that, I have written my own programme, in MatLab. It is be able to load data almost directly from the International Seismic Center and make an inversion in a given area. The data used for inversion will be the Richter magnitude of regional earthquakes recalculated to a delta(1/Q). And the goal of the thesis is an improved mapping of crustal structure differences. This is, amongst other uses, directly applicable for the oil industries of Denmark, because oil and gas fields are located at the structural differences known as the Central Graben and Wiking. Other important geological differences are known to be connected to differences in the crustal structure. Depending on the amount of time available I'll try to use different inversion techniques, and experiment with the resolution in order to get the best map of the crustal differences. Søren Gregersen did a similar investigation back in the 80's of the middle of the North Sea bassin, so I'll have some results to compare with, even though he had fewer data available to him at the time. To summarize; I'm expecting to have a finished map of the delta inverse quality factor from Lg waves and this will be compared to earlier investigations, and further more I'll be having a MatLab programme that others will be able to use for similar investigations.

Advisor: Klaus Mosegaard