HR: 09:20h
AN: S11C-06    [Abstracts]
TI: Strongly localized near-coastal generation areas for $\sim$4 s microseismic noise in the North-East Atlantic
AU: Dahm, T
EM: dahm@dkrz.de
AF: Institut f. Geophysik, Univ. Hamburg, Bundesstr. 55, Hamburg,, 20146 Germany
AU: * Tilmann, F J
EM: tilmann@esc.cam.ac.uk
AF: Bullard Laboratories Department of Earth Sciences University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Morgan, J
EM: jpm@geology.geo.cornell.edu
AF: IFM-GEOMAR, Wischofstr 1-3, Kiel, 24148 Germany
AB: Mapping the generation areas for ocean-generated microseismic noise is of importance both for the planning of future ocean bottom experiments and for the use of historical seismological microseismic noise data as a proxy for ocean wave height in historical climate studies. We report on the results of a large aperture (400 km), 3 month pilot deployment of 10 ocean bottom stations (7 seismometers/hydrophones, 3 hydrophones) in the North Atlantic south of Iceland. The noise level was found to be highly variable both with time and for the different stations, and shows marked variability between bands. By correlating noise levels recorded on the ocean bottom stations as well as on nearby land stations with wave height data for the same period, we map out estimated generation areas for microseismic noise. For high frequency noise (0.5--2 Hz) the noise turns out to be predominantly related to local waves, and for lower frequency noise ($<$0.3~Hz) noise seems to originate mainly in a few source regions near the coasts of Ireland, Scotland and Iceland. The generation areas for the ocean bottom instruments were similar to those of land instruments in the same region. It should thus be possible to estimate the generation areas for proposed future ocean bottom installations based on nearby land stations, and thus allow better estimates of expected noise levels than those derived from regional averages of typical weather conditions. The directivity of noise suggests optimised array designs for noise suppression. Below the microseismic band and at the relatively noisier stations, the vertical seismograms at frequencies below $\sim$0.3 Hz could be substantially enhanced by removing the part correlated with the horizontal components, suggesting that noise introduced by instrument tilt was considerable at those stations.
DE: 7299 General or miscellaneous
DE: 4247 Marine meteorology
DE: 3094 Instruments and techniques
SC: Seismology [S]
MN: 2004 AGU Fall Meeting