Rapid extraction of central vacancy by image-analysis of Fry plots |
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| Institution: | 1. CICESE, División de Ciencias de la Tierra, Departamento de Geofísica Aplicada, Carretera Ensenada-Tijuana No 3918, Fraccionamiento Zona Playitas, Ensenada, Baja California Postal Code 22818, Mexico;2. Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de Mexico, Blvd L.D. Colosio S/N y Madrid, A.P. 1039, Hermosillo, Sonora Postal Code 83240, Mexico |
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| Abstract: | The Fry method, based on the relative movement of different material points, typically grain centers, with reference to each other graphically yields a point distribution that displays the finite strain ellipse as a central vacancy. The diffused nature of the central vacancy induces subjectivity in strain estimation, particularly, if the point population when undeformed lacked an isotropic anticlustered distribution. Most existing methods use analytical and/or iterative approaches for improving the sharpness of the central vacancy and positioning the best-fit strain ellipse in a Fry plot. We provide an image-analysis method that is independent of any iteration or analytical solution. It is also an efficient technique for extraction of the central vacancy without any subjectivity. The method is more direct, simple and easy-to-use than most existing techniques.The image-analysis method uses Gaussian blur filter for distinction between the areas of largest and smallest pixel intensities in a Fry plot image. It then applies the optimal threshold value and an inversion filter for extraction of the sharp central vacancy. The method also searches for the best-fit strain ellipse through the extracted central vacancy and displays axial ratio and orientation of the ellipse in a separate window. The validity of the method is tested using several computer-simulated and natural examples. |
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