Structural geology . Fig. Wire netting model undeformed. See also Figs. 6 and the use of the sphere as the unit of original structure and the strainellipsoid as its deformed equivalent. Fractures under compressiontend to follow the cross sections in the strain ellipsoid which are thesame in dimensions as those of the original sphere; in other words,planes (called planes of no distortion) determined by the intersec-tions of the original sphere with the strain ellipsoid. COMPRESSION FRACTURES 19 A simple device for illustrating the position of strain ellipsoidand shearing planes in both rotation
Structural geology . Fig. Wire netting model undeformed. See also Figs. 6 and the use of the sphere as the unit of original structure and the strainellipsoid as its deformed equivalent. Fractures under compressiontend to follow the cross sections in the strain ellipsoid which are thesame in dimensions as those of the original sphere; in other words,planes (called planes of no distortion) determined by the intersec-tions of the original sphere with the strain ellipsoid. COMPRESSION FRACTURES 19 A simple device for illustrating the position of strain ellipsoidand shearing planes in both rotational and non-rotational strainis shown in Figs. 5, 6; and 7. A cardboard upon which is inscribeda circle is laid between two sheets of wire netting. The three arethen fastened together by a rivet in the center of the circle. Awooden hinged frame fastened to the netting allows and controlsthe distortion of the netting, while the interior sheet remains undis-. Fio. 0. Wire netting model deformed by non-rotational strain. Straight linesconnecting intersections of circle and ellipse mark positions of planes of nodistortion or planes of maximum shear. torted. A circle and diameters are painted on the netting corre-sponding with those on the central sheet. AVhen the screen isdistorted the circle on the wire becomes an ellipse or a cross sectionthrough the greatest and least principal axes of a strain ellipsoid,which is superposed upon the undeformed circle of the Fig. 6 a non-rotational strain is represented, called pureshortening and elongation. The circle elongates normal to the 20 STRUCTURAL GEOLOGY maximum shear, stand normal to the surface of the screen. Theirintersections with the plane of the screen are to be seen at about45° to the pressure. It will be noted that the lines representing theplanes of shear are parallel to the wires. The distortion of thescreen actually occurs by shearing of the wire mesh. This should KALEVIM
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