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Liang, Beiyuan, 1992

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Liang, Beiyuan, 1992, Orientation and magnitude of principal stresses in seismically active regions from the inversion of focal mechanisms and other geophysical data: University of Colorado, Boulder, Ph.D. dissertation, 286 p.


The stress state in the crust or lithosphere is investigated in several seismically active regions: southeastern Hawaii, the Central Aleutian Islands, and the Reykjanes Peninsula of Iceland. We use stress orientation inversion based on focal mechanisms to estimate the principal stress directions in a seismic volume. We then employ the directions as constraints, combined with geodetic data and the seismic wave velocity structure, to invert for the magnitude and distribution of the complete stress tensor (stress magnitude inversion). Seismically-released strain in a seismic volume is calculated (seismic strain calculation). In order to investigate tectonic characteristics, we compare the principal directions of stress and seismic strain, and the geodetically-observed and seismically-released strains. All these methods are successfully applied to the south flank of Kilauea volcano, Hawaii. The principal stress and strain directions are approximately uniform with space and time. However, the [sigma]1,[sigma]3 plane is almost orthogonal to [epsilon]1,[epsilon]3 plane. Therefore, a weak layer beneath the flank may exist. The direction of [sigma]1 can be interpreted as the superposition of gravity and magmatic pressure. The maximum magmatic pressure at the boundary of the seismic volume is about 160 MPa. In the Kaoiki and Hilea areas of Hawaii and the Reykjanes Peninsula of Iceland, the statistically significant results for the principal stress direction are obtained. In Kaoiki, the heterogeneous stress state distributes in a 10 x 10 x 10 km3 volume. However, in the 200 x 40 x 50 km3 section of the central Aleutian Islands, the solution of the principal stress directions shows great uncertainty due to the fact that almost all focal mechanisms are very similar. In all the areas of Hawaii, a difference between the principal stress and seismic strain directions is found. This suggests that the interpretation of the P and T axes of focal mechanisms as the principal stress directions is not reliable. Stress orientation inversion, seismic strain calculation and stress magnitude inversion used in this study can provide an approach to the estimation of the stress state in the crust or lithosphere. We intend to apply the entire procedure and further test it at plate boundaries and other places in plate interiors in the future.

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