McGill Structural Geology

Jamie Kirkpatrick

Our Work

We use ground-based LiDAR, differential GPS (dGPS), and the Structure-from-Motion method to collect digital field data to measure the properties of fault zones and other deformation structures in the field. In the lab, we carry out microstructural work using SEM (and EBSD), TEM, microprobe and micro-scale surface pofiling instruments and quantify the effects of deformation using statistical and numerical models. The goals are to develop new methodologies for investigating rock mechanics in the field and ultimately bridge the divide between structural geology and seismology. Below are some research themes that are current and ongoing in the group.

Corona Heights fault

Fault geometry and mechanics

Faults are geometrically complex. When the various bumps and depressions on either side of a fault interlock, they control the static strength of the fault and dynamic earthquake source parameters. We are using new tools to measure the shape and distribution of different components of fault zones, such as slip surfaces or damage zones, to investigate how the geometry of faults impacts mechanical strength. This approach allows us to address questions like these:

  • Slickenlines record fault displacement vectors - can we use them to constrain tectonic stresses?
  • Damage zones form partly due to stress concentrations resulting from geometric complexity - can we use damage zones to estimate fault friction
  • Principal slip zones are non-planar - can we simulate the boundary geometry and test the implications for stability in the lab?
  • Fault growth requires stress concentrations at the propagating tip - can we measure this in recently active fault systems?
Steelhead Lake fault

Faults and fluid flow

When faults, fractures and joints form in the crust they represent open cracks through which fluids can flow. The development of these structures is therefore critical to groundwater, mineral and hydrocarbon resources. However, fluids reduce the effective stresses at depth, and promote brittle failure so fluids catalyze deformation. We are investigating this interrelationship mapping deformation structures in the field, measuring the geometrical characteristics that impact permeability, and defining the timing of fluid flow.

Fluid assisted shear fracture

Tremor in the rock record

Tectonic tremor is recorded seismologically as bursts of low frequency earthquakes that occur on subduction zones and some transform faults, such as the San Andreas fault. These tiny earthquakes occur at depths where aseismic creep is thought to predominate, and are associated with slow slip events. Because tremor was only discovered recently, and because the events occur at depth not much is known about the geological conditions and processes that drive them. We are investigating fluid assisted shear fractures in ductile shear zones to find out if they could be analog structures that can reveal the source of the tremor. What causes ductile shear zones to fracture? Can we understand the mechanical interactions between tremor, slow slip and earthquakes in the seismogenic zone?