On the nature of regional seismic phases–II. On the influence of structural barriers |
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| Authors: | T Furumura B L N Kennett |
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| Institution: | Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia |
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| Abstract: | The blockage of the L g wave by crustal barriers such as continental margins and graben structures has long been recognized as providing a very useful tool for mapping large-scale lateral crustal variations along the propagation path. Numerical simulation of L g -wave propagation in complex anelastic media using the pseudospectral method provides insight into the nature of the propagation process using both snapshots of the wavefield and synthetic seismograms. A variety of 2-D structures have been investigated, including the influence of sediments, crustal thickness and attenuation.
Thick sedimentary basins covering a graben structure can have a major influence, since they remove L g energy by generating P conversion and scattering–the principal mechanisms for strong L g attenuation across a graben. The reduction of the L g energy is reinforced by anelastic attenuation in the sediments as well as the influence of the gradually thinning crustal waveguide associated with an elevated Moho.
The extinction of L g in a sequence of explosions fired across the central graben of the North Sea can be simulated by numerical calculations for the structure derived from refraction experiments. |
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| Keywords: | lateral heterogeneity L g wave Moho discontinuity North Sea Central Graben nuclear explosions seismic modelling synthetic seismograms wave propagation |
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