SZ

3.5 Shear Zone Event

In order to define an shear zone or kink event, place an shear zone icon in the History window. You will then be provided with the Shear zone definition window.

Shear Zone Definition Window

Shear zones and kinks are parallel sided zones of simple shear which share the same overall geometries as faults. The cross-sectional profile of the shear zone can either be sharp (kink) or smooth (shear zone).

GROUP	NAME	FUNCTION
Form	Type:
	Shear Zone	Smoothly varying displacements across shear zone
	Kink	Kink like displacement profile
	Geometry:
	Translation	Simple planar translational shear zones
	Rotation	Simple planar rotational shear zones
	Elliptical	Elliptical shear zone Elliptical fault plane, these shear zones displace material within an ellipsoidal zone defined by the long axes of the ellipsoid, with slip vectors dying off away from the centre of the ellipsoid.
	Curved	Curved shear zone Curved fault plane, essentially an elliptical shear zone with a curved shear zone surface, which is defined by its profile, and the amount of decay of the curvature away from the plane of definition.
	Ring	Ring shear zoneRing fault, producing a cylindrical volume of slipped material. Dip and Dip Direction are actually the to Plunge and Plunge Direction of central axis of ring shear zone.
	Movement:
	Hanging Wall	Hanging wall Hanging wall only movement on shear zone (hanging wall is inside of ring shear zone).
	Foot Wall	Foot wall Foot wall only movement on shear zone (foot wall is outside of ring shear zone).
	Both	Both footwall and hanging Both footwall and hanging wall. The total slip vector is divided into 50% movement in each direction.
	Alterations:
	None	No alteration halo associated with this event
	Top	Alteration halo on hanging wall side of shear zone
	Bottom	Alteration halo on foot wall side of shear zone
	Both	Alteration halo on both sides of shear zone
	Edit	Brings up Alteration Profile window
	Show Profile	Shows Profile Definition window for Curved Shear zones
Surface Shape	Flat Plane	Shear zone plane defined only by Geometries options (see above)
	DXF Surface	Part of shear zone plane defined by DXF triangulated surface
	View	View grey scale image of DXF surface topography
	X Dim	Scaling factor for X direction of plane
	Y Dim	Scaling factor for Y direction of plane
	Z Dim	Scaling factor for Z direction of plane

Position	X	X position of one point on shear zone plane (centroid of elliptical and curved shear zones, centre of rotation of rotational shear zones, top right hand corner of DXF surface bounding rectangle)
	Y	Y position of one point on shear zone plane
	Z	Z position of one point on shear zone plane
Orientation	Dip Dir	Dip Direction of Shear zone Plane
	Dip	Dip of Shear zone Plane
	Pitch	Pitch of slip vector on shear zone plane
	Trace From Image	Allows orientation of shear zone to be traced directly from BMP format (PICT on Mac) file.
Scale	Rotation	Rotation of shear zone block in degrees, around normal to shear zone passing through X,Y,Z, anticlockwise looking down rotation axis
	Slip	Displacement on shear zone parallel to slip vector
	Amplitude	Amplitude of curvature of shear zone, as defined on profile
	Width	Width of shear zone
	Radius	Radius of Ring Shear zone
	Cyl Index	Cylindricity index for decay of curvature of curved shear zones. Distance perpendicular to profile at which amplitude drops to 1/2 following a exponential drop-off
	Profile Pitch	Orientation of Curved Shear zone Profile (Independant of Slip Vector Pitch)
Scale (Ellipsoid)	X Axis	Long axes of ellipsoid for elliptical shear zones (X=slip direction, XZ plane = shear zone) The magnitude of the chosen slip vector must always be less than the X value.
	Y Axis	Magnitude of ellipsoid normal to shear zone plane
	Z Axis	Magnitude of ellipsoid normal to slip vector

Tracing Shear Zone Orientations From Maps

When the Trace From Image Button is selected, the program will ask for a .BMP format (or PICT format on the Mac) image from which fault trends can be traced directly, and also calculates the position. The scaling is determined by the Fault Trace Control Window, which determines the coordinates of the NW and SE corners. The two points on the fault trace may be defined by clicking in the Image window, and may be edited by dragging them.