Details

Autor(en) / Beteiligte

• Cembrowski, Marcel
• Junge, Andreas

Titel

Electrical anisotropy in the presence of oceans—a sensitivity study

Ist Teil von

• Geophysical journal international, 2018-05, Vol.213 (2), p.1029-1043

Ort / Verlag

Oxford University Press

Erscheinungsjahr

2018

Beschreibungen/Notizen

• Summary Electrical anisotropy in the presence of oceans is particularly relevant at continent–ocean subduction zones (e.g. Cascadian and Andean Margin), where seismic anisotropy has been found with trench-parallel or perpendicular fast direction. The identification of electrical anisotropy at such locations sheds new light on the relation between seismic and electrical anisotropies. At areas confined by two opposite oceans, for example the Pyrenean Area and Central America, we demonstrate that the superposed responses of both oceans generate a uniform and large phase split of the main phase tensor axes. The pattern of the tipper arrows is comparatively complicated and it is often difficult to associate their length and orientation to the coast effect. On the basis of simple forward models involving opposite oceans and anisotropic layers, we show that both structures generate similar responses. In the case of a deep anisotropic layer, the resistivity and phase split generated by the oceans alone will be increased or decreased depending on the azimuth of the conducting horizontal principal axes. The 3-D isotropic inversion of the anisotropic forward responses reproduces the input data reasonably well. The anisotropy is explained by large opposed conductors outside the station grid and by tube-like elongated conductors representing a macroscopic anisotropy. If the conductive direction is perpendicular to the shorelines, the anisotropy is not recovered by 3-D isotropic inversion.