How is the daylight envelope on a stereonet constructed?

The Daylight Envelope is simply the locus of all pole vectors whose corresponding plane (dip vector) lies exactly on the slope plane.


Kinematic analysis results for planar sliding (see Tutorial 4 for more information)


The envelope is calculated by taking the trend and plunge of a number (say 30 or 45) of sequential points on the slope great circle (starting at one equator and moving to the other).  For each successive point, calculate a daylight pole point at trend+180, 90-plunge and connect the dots to get the daylight envelope.

The daylight envelope represents all planes which can theoretically daylight from a given slope.  In practice, planes which have a similar dip direction to the slope plane are more likely to fail, so angular limits can be placed (typically plus/minus 20 degrees or so) to decrease the number of critical planes.

Note:  to display the dip vector “tic” for a user plane, right-click on the plane after adding, select Edit User Plane from the popup menu, and select the Marker Ticks checkbox.