Department of Geophysics
Utrecht University, PO Box 80.021, 3508 TA Utrecht, The Netherlands
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The stable East European Platform (EEP) adjoins tectonic Central and Western Europe (TE) along the Tornquist-Teisseyre Zone (TTZ). Seismic studies indicate a significant change in S wave velocity at the top of the mantle across the TTZ, with higher velocities under the EEP. Recently, we used a genetic algorithm (GA) (Lomax and Snieder, 1995b) to invert Rayleigh group-velocity data for paths across TE and the EEP to determine "average", layered S velocity models separately for each region. The GA allows an identical, non-linear search to be used for both regions giving a relatively unbiased estimate of the difference in structure. However, the GA uses a poor sampling of the model space and consequently the uncertainty in the results are not well defined ( Lomax and Snieder, 1995a; Lomax and Snieder, 1996).
Here, we repeat this inversion using an adaptive, Monte-Carlo importance sampling algorithm (AMI) which has improved sampling of the model space. This method produces approximate likelyhood functions at each depth giving a better understanding of the uncertainty and resolutions of the inversion. The new results confirm the earlier GA results but give clearer and more quantitative images of features including velocity-depth trade-offs around the Moho, the maximum depth resolution, and the contrast in upper mantle S velocity.
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In the figures below we show the AMI inversion results for the EEP and TE dispersion data. In each figure the left frame shows the sampling density at each depth in the model space, the center frame shows relative likelyhood for S velocity at each depth. The right frame shows the acceptable models, those models that fit the data within a cutoff based on the scatter in the data.
Anthony Lomax - firstname.lastname@example.org
Last update: 15 Dec 1995