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O'Brien G.S.,Geophysical Technology and Operations
Computers and Geosciences | Year: 2014

Elastic lattice methods (ELMs) have been shown to accurately model seismic wave propagation in a heterogeneous medium. These methods represent an elastic solid as a series of interconnected springs arranged on a lattice and recover a continuum wave equation in the long wavelength limit. However, in the case of a regular lattice, the recovery of the continuum equation depends on the symmetry of the lattice. By removing particles above a free surface this symmetry is broken. Therefore, this free surface implementation leads to errors when compared with a traction free boundary condition. The error between a traction free boundary condition and the ELMs grows as the Poisson[U+05F3]s ratio deviates from 0.25. By modifying the interaction constants with a scalar, the error can be reduced while keeping the flexibility of the nearest neighbour interaction rule. We present results of simulations where modified spring constants reduce the misfit with a traction free boundary solution and hence increase the accuracy of the elastic lattice method solution on the free surface. © 2014 Elsevier Ltd.

Martini F.,Geophysical Technology and Operations | Davi R.,Geophysical Technology and Operations | Doherty J.,Geophysical Technology and Operations | Mongan J.,Geophysical Technology and Operations
First Break | Year: 2015

Passive recording of background noise have been successfully used to retrieve information about the large-scale structure of a sedimentary basin. Ambient noise can be used to retrieve velocity profiles in order to investigate the velocity structure and the depth of a sedimentary basin, in an unexplored area and/or when additional constraints on the basement depth may be needed for interpretation of active seismic or non-seismic data. We exploit techniques usually used in geotechnical or earthquake hazard/engineering studies. Surface wave dispersion analy sis can be used to obtain 1D velocity-depth profiles below an array of seismic stations which record passive ambient noise. Analogously, the horizontal-to-vertical spectral ratio of both the surface and body waves can provide 1D velocity-depth profiles below standalone seismic stations which record passively ambient noise. We successfully applied this technique in Uganda, Ethiopia and Kenya, where field surveys were carried out to recover the depth to basement. With this work we present and discuss the results we obtained in those areas, the accuracy of which was validated by comparing with depth values obtained by other seismic and non-seismic datasets (independently acquired and processed). © 2015 EAGE www.firstbreak.org.

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