Project Results Cont.
Total Shear Strain
Below are contour maps of the total shear strain field for each of the epochs of terrane collision. Total shear strain was calculated using the following formula:

G = (g12 + g22)0.5

Where:

g1 = Pure Shear Strain Component (dDx/dx - dDy/dy)

g2 = Simple Shear Strain Component (dDx/dy + dDy/dx)
Epoch 1: Time step between photos 1 and 2. Note that the strain is concentrated at the toe of the wedge, as would be expected from critical wedge theory. The displacement velocity vectors are indicated by the arrows.
Epoch 2: Time step between photos 2 and 3. This is the time just prior to collision between the terrane and the wedge. Note that the strain is concentrated at the toe of the wedge. The displacement velocity vectors are indicated by the arrows.
Epoch 3: Time step between photos 3 and 4. This is the time of initial collision between the terrane and the wedge. Note that strain is still concentrated at the toe of the wedge, but the region is no longer arcuate (this agrees with what is observed in the photo). The displacement velocity vectors are indicated by the arrows.
Epoch 4: Time step between photos 4 and 5. Note that strain is more broadly distributed and that there are local concentrations in the terrane. However, this is not evident by visual inspection of the photos because no faults are developed in the terrane. The displacement velocity vectors are indicated by the arrows.
Epoch 5: Time step between photos 5 and 6. Note that strain is once again concentrated in the area at the toe of the wedge. This is supported by the observation that thrusts have developed in the terrane, localizing the strain. Also note the concentration of strain near the back of the wedge, which coincides with the location of major thrusting in the overriding wedge. Velocity displacement vectors are indicated by the arrows.
Epoch 6: Time step between photos 6 and 7. Strain is more broadly distributed throughout the orogen. This coincides with the development of a decollement at the base of the accreted terrane and the focussing of deformation at the toe of the terrane. Velocity displacement vectors are indicated by the arrows.
Epoch 7: Time step between photos 7 and 8. Note that strain is starting to become more concentrated at the toe of the accreted terrane, which is consistent with what is observed in the photos. Velocity dislacement vectors are indicated by the arrows.
Epoch 8: The final state of strain. Note here that the strain field outlines the toe of the orogen and that there is some localization in the terrane. This is consistent with what is observed in the photos in that there is some shortening within the terrane at this time. Velocity displacement vectors are indicated by the arrows.
Total Shear Strain