Global Tomography With Long Period P Waves In Resolution-matched Grids
Abstract
Long period travel times, often measured using cross-correlation techniques, suffer from the effects of wavefront healing. Their sensitivity to Earth structure is markedly different from the sensitivity as predicted by asymptotic ray theory. We present the results of an inversion of delay times measured for P waves with a dominant period of 20 s, using the `banana-doughnut' kernels derived by Dahlen, Hung and Nolet (GJI, 2000). These kernels have significant small scale structure. Commonly applied proxies for resolution, such as ray density, are likely to be incorrect. For this reason we also developed a novel technique of model parameterization.
In our study, we use Delaunay meshes to represent the velocity structure. To obtain a first order estimate of the resolving power as a function of location in the Earth, we compute the diagonal elements of the resolution matrix using the theory of Nolet, Montelli and Virieux (GJI, 1999) and use these to re-design the interpolation grid, either by construction or by minimization of an almost quadratic penalty function. For a smaller data set of some 40,000 P waves, the resolution is more homogeneous when we take the finite frequency effects into account, than when we compute the resolution using asymptotic ray theory. The resulting tomographic model shows more continuity of structures such as the Farallon plate when inverted with banana-doughnut kernels. We suspect that these differences will only become more pronounced when we expand the data set to include more data, so that we can use a finer parameteri- zation. We shall present the latest results of our inversions and discuss the improve- ments brought about in the imaging by incorporating the effects of finite frequency and resolution-guided parametrization.- Publication:
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EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.3587M