Hur viktig är kemisk bandning i jordens inre? Hypotesprovning genom användning av seismisk anisotropi
Tidsperiod: 2019-01-01 till 2022-12-31
Projektledare: Bjarne Almqvist
Medarbetare: Hem Bahadur Motra, Mattia Pistone, Sandra Piazolo, David Mainprice, Tomas Lokajicek
Budget: 3 600 000 SEK
Seismological observations indicate that large regions within Earth show directionally dependent seismic wave speeds. Such seismic anisotropy is a unique and invaluable indicator for material transport, structure and rheology of the Earth. However, a challenge in using seismic anisotropy is that it arises from different sources, leading to non-unique interpretations of its origin. Intrinsic anisotropy originates from single crystals, or aggregates of oriented crystals, which is known as crystallographic preferred orientation (CPO). It is an important source for anisotropy, generally related to flow of material in the deeper parts of the crust, mantle and core. Extrinsic, or apparent, anisotropy arises from geometrical effects such as layering of rocks, and oriented crack and fluid networks. In this project, particular focus is placed on testing the hypothesis that mineral compositional banding is an important extrinsic contributor to seismic anisotropy. Field work will be conducted to map and collect representative layered rocks for a wide range of rock types, and analyses include detailed microstructural and CPO determination. Seismic velocities and anisotropy are determined using combined state-of-the-art laboratory measurements and modelling methods. Results are expected to increase capability to interpret seismic anisotropy, and shed light on geodynamic processes of Earth´s interior, which cannot be addressed with any other geophysical method.