Formation & Geometry of Normal Faults Flashcards
Griffith cracks / tension cracks
Cracks that form perpendicular to the least compressive stress
Mohrs diagram
Normal stress (x-axis)
Sheer stress (y-axis)
Defines the stresses on a plane by creating a relation between sigma_1 (Maximum compressive stress) and sigma_3 (Minimum compressive stress) where 2*sigma (angle) is equal to the normal and sheer stresses that act on a plane
Mohrs envelope
Predicting the orientation of the fracture and the forces acting
The Mohr–Coulomb[7] failure criterion represents the linear envelope that is obtained from a plot of the shear strength of a material versus the applied normal stress. This relation is expressed as
tau=sigma*tan(ø)+c
Conjugate faults
Two opposite sets of faults with the same dip. This will create a triangle
Bimodal conjugate fault set
Fault sets of conjugate faults that when plotted in a stereonet create two points
The relation between the maximum cumulative displacement and length
d_max=c*L^n
D=L^2/P
d_max: Maximum displacement (D)
L: fault length
n: Empirical determined value
c=1/P: constant depending on the material
How do you measure the length and depth of a fault?
It is typically done through seismic data. It’s important to remember the same fault measured in differing places will plot differently in length.
Seismic resolution
Defines the minimum offset which can be observed
This means the observable length through seismic data is shorter than the actual length
Ductile deformation
Ductility refers to the capacity of a rock to deform to large strains without macroscopic fracturing
Reverse drag
A reverse fault where the layers will drag and curl slightly. Effects from reverse drag are found far away from the fault. There’s a footwall uplift.
Perceptible reverse drag radius:
r= 0.2W=0.4R
How do faults grow?
- Earthquakes single slip events
- Growth of a single fault
-Segmentation and linkage
