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Field geology

Stereonet Lab

Orientation statistics, pole density, rose diagrams and kinematic counts on the lower hemisphere.

Analyses any number of planes and lines measured in the field or with the phone: pole density contours, Fisher statistics of each set, eigenvalue fabric and π-girdle axis, rose diagram of strikes, and the percentage of measurements critical for planar, wedge and toppling failure against a slope face.

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Stereonet Lab
NBedding 045/38Slope face 060/62Joint sets J1, J2Friction cone φ = 30°Planar slidingPossibleRMR 47 · Class III

Overview

Measurements are entered as dip direction / dip or right-hand-rule strike / dip, imported from CSV, pasted from a field sheet or recorded with the phone compass-clinometer and corrected to true north with the IGRF-14 declination. Sets are taken from the field labels or detected automatically by axial k-means.

Pole density gives where the measurements concentrate; Fisher statistics give the mean orientation of each set and its precision; the eigenvalues of the orientation tensor tell a cluster from a girdle and yield the statistical fold axis; the kinematic counts give the proportion of discontinuities able to fail toward a given slope face.

What you enter · What you get

What you enter

  • Planes: dip direction and dip, or strike (RHR) and dip
  • Lines: trend and plunge
  • Set labels or the number of sets
  • Site position for the magnetic declination
  • Slope face, friction angle and lateral limits (optional)

What you get

  • Pole density contours in MUD with set means and α95 cones
  • Mean planes, intersections, eigenvectors and π-girdle
  • Rose diagram of strikes with axial mean
  • Kinematic stereonet with critical percentages
  • Directional hazard radar
  • Set statistics table and CSV exports

How it works in the field

Record or import planes
Assign the sets
Read the statistics
Test against the face
Export

Method and equations

Projection

Lower-hemisphere equal-area (Schmidt) projection for statistics and density, equal-angle (Wulff) for angular construction.

rSchmidt = √2·R·sin(θ/2)  ·  rWulff = R·tan(θ/2)

Pole density (Vollmer 1995)

Exponential Kamb smoothing; densities are expressed in multiples of a uniform distribution (MUD).

W = exp[k(|cos θ| − 1)], k = 2(1 + N/9)

Fisher statistics (Fisher 1953)

Mean orientation of each set, precision parameter and the 95 % cone of confidence of the mean.

k = (N − 1)/(N − R)  ·  cos α95 = 1 − (N − R)/R·[201/(N−1) − 1]

Orientation tensor (Woodcock 1977)

Eigenvalues S1 ≥ S2 ≥ S3 distinguish clusters (K > 1) from girdles (K < 1); E3 of a girdle is the π-axis.

K = ln(S1/S2) / ln(S2/S3)  ·  C = ln(S1/S3)

Kinematic counts

Planar and toppling tests on every dip vector, wedge test on every intersection of two planes (Markland 1972; Goodman & Bray 1976); results as percentages of the total.

φ < ψj < ψf, |αj − αf| ≤ 20°  ·  φ < ψi < ψfi

Who uses it

Structural geologistsEngineering geologists and mining engineersResearchers and students of structural geology

Standards and references

  1. Fisher, R.A. (1953). Dispersion on a sphere. Proceedings of the Royal Society of London A, 217, 295–305.
  2. Goodman, R.E. & Bray, J.W. (1976). Toppling of rock slopes. Proc. ASCE Specialty Conference on Rock Engineering for Foundations and Slopes, Boulder, 2, 201–234.
  3. Hocking, G. (1976). A method for distinguishing between single and double plane sliding of tetrahedral wedges. Int. J. Rock Mech. Min. Sci., 13, 225–226.
  4. Kamb, W.B. (1959). Ice petrofabric observations from Blue Glacier, Washington, in relation to theory and experiment. Journal of Geophysical Research, 64, 1891–1909.
  5. Markland, J.T. (1972). A useful technique for estimating the stability of rock slopes when the rigid wedge type of failure is expected. Imperial College Rock Mechanics Research Report 19.
  6. Vollmer, F.W. (1995). C program for automatic contouring of spherical orientation data using a modified Kamb method. Computers & Geosciences, 21, 31–49.
  7. Woodcock, N.H. (1977). Specification of fabric shapes using an eigenvalue method. Geological Society of America Bulletin, 88, 1231–1236.
Results support professional judgement. They do not replace a licensed engineer’s or geologist’s sign-off.

At a glance

Category
Field geology
Runs on
Phone, tablet and desktop browser
Export
PDF report, PNG figures, CSV
Access
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