Assessing the role of effective medium theory in the formation of primary low-angle normal faults

The origin of low-angle normal faults is highly debated. Previous studies have shown that some low-angle normal faults form with steep initial dips before rotating to present-day low-angle configurations while other low-angle normal faults are primary in the sense that they initially formed with dip angles of 30 degrees or less. One of the mechanisms enabling the formation of primary low-angle normal faults is material anisotropy. Here, we explore the role of the effective medium theory (EMT), an anisotropic constitutive model describing effective elastic properties for cracked solids. Previous rock deformation studies have successfully verified the effectiveness of EMT for estimating elastic anisotropic properties of progressively damaged rocks. However, to our knowledge, this model has not been considered in a study of fault formation and orientation. Implementing EMT in DES3D, an open-source long-term tectonic modeling code, we investigate whether and how EMT can promote the formation of primary low-angle normal faults by changing in-situ properties. Being a non-interaction approximation for crack contributions, EMT is dependent on two key parameters: crack density and crack orientation. We present preliminary results for the sensitivity of initial dip angles of normal faults in two-dimensional cross-sectional models for continental crust to these parameters.