Measurement and confirmation of tectonic stress directions using three-component seismic data
Global Seismology Research Group, British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, Scotland UK.
Global Seismology Research Group, British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, Scotland UK.
Geochemistry Directorate, British Geological Survey, Nicker Hill, Keyworth, Nottingham NG12 5GG, England UK.
Abstract
Analysis of all suitable recordings of three-component seismic data, from both earthquake and man-made sources, reveals that the shear-waves display characteristic shear-wave splitting with preferential directions of polarization. Modelling experiments indicate that this behaviour is caused by shear-waves propagating through distributions of stress-aligned, parallel, vertical, liquid-filled inclusions. Such distributions of inclusions, which can have many shapes, are known to permeate, and shear-waves indicate that they are aligned, throughout at least the upper 10 to 20 km of the Earth's crust in a variety of tectonic environments. Various parameters of these inclusions can be estimated by analysing shear-waves, such as the crack density, and, most important, their orientation which is parallel to the direction of maximum horizontal compressive stress causing the orientation. Such research has important implications in hydrocarbon and geothermal reservoir monitoring, earthquake prediction, mining, and in many other geological fields in which a knowledge of the cracks and stress is important. The results of such monitoring will be demonstrated. It is suggested that our knowledge of stress directions in NW Europe could be considerably improved by analysis of more three-component seismic data.
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