HR: 0800h
AN: S51E-1059    [Abstracts]
TI: A Neighbourhood Algorithm Analysis of the Constraints Provided by Surface Wave Dispersion Data on Upper Mantle Structure
AU: * Beghein, C
EM: beghein@mit.edu
AF: MIT, 77 Massachusetts avenue #54-526, Cambridge, MA 02139 United States
AU: Lebedev, S
EM: sergei@geo.uu.nl
AF: Utrecht University, 4 budapestlaan, Utrecht, 3584 CD Netherlands
AU: van der Hilst, R
EM: hilst@mit.edu
AF: MIT, 77 Massachusetts avenue #54-526, Cambridge, MA 02139 United States
AB: Interstation dispersion curves can be used to obtain regional 1D profiles of the crust and upper mantle. Unlike phase velocity maps, dispersion curves can be determined with small errors and for a broad frequency band. We want to determine what features interstation surface wave dispersion curves can constrain. Using synthetic data and the Neighbourhood Algorithm, a direct search approach that provides a full statistical assessment of model uncertainites and trade-offs, we investigate how well crustal and upper mantle structure can be recovered with fundamental Love and Rayleigh waves. We also determine how strong are the trade-offs between the different parameters and what depth resolution can we expect to achieve with the current level of precision of this type of data. Synthetic dispersion curves between approximately 7 and 340s were assigned realistic error bars, i.e. an increase of the relative uncertainty with the period but with an amplitude consistent with the one achieve in ``real'' measurements. These dispersion curves were generated by two types of isotropic model differing only by their crustal structure. One represents an oceanic region (shallow Moho) and the other corresponds to an archean continental area with a larger Moho depth. Preliminary results show that while the Moho depth, the shear-velocity structure in the transition zone, between 200 and 410km depth, and between the base of the crust and 50km depth are generally well recovered, crustal structure and Vs between between 50 and 200km depth are more difficult to constrain with Love waves or Rayleigh waves alone because of some trade-off between the two layers. When these two layers are put together, the resolution of Vs between 50 and 100km depth apperas to improve. Stucture deeper than the transition zone is not constrained by the data because of a lack of sensitivity. We explore the possibility of differentiating between an upper and lower crust as well, and we investigate whether a joint dataset composed of both Love and Rayleigh wave measurements can improve the constraints on upper mantle structure compared to distinct Love and Rayleigh wave datasets. We also determine how well this type of data can constrain the presence of a low velocity zone and the presence of radial anisotropy.
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: Fall Meeting 2005