How do horizontal, frictional discontinuities affect reverse fault-propagation folding?

Testing Different Tectonic Models for the Source of the Mw 6.5, 30 October 2016, Norcia Earthquake (Central Italy): A Youthful Normal Fault, or Negative Inversion of an Old Thrust?

“…is characterized by alternating limestones, marls, and clays. In such rock types, the cyclical transition between strong and weak layers suggests that the kinematic model to be preferred is the kink‐band fold‐propagation fault for reverse faults (Bonanno et al, ; Hughes & Shaw, ) and a flexural slip model for the extensional structures. All younger formations, from Paleogene to Quaternary, are dominated by weak rocks. In this case, our preferred model is trishear fault‐propagation fold.…”

“…If a weak layer located above a propagating fault causes its plane to be refracted (i.e., steepening for extensional faults and shallowing for reverse faults) and its characteristic propagation‐to‐slip ratio to be delayed, the role of a frictional weakness becomes more complex. Several investigators have explored this effect using analog and numerical models (e.g., Albertz & Sanz, ; Bonini et al, ; Bonini, Basili, et al, ; Bonanno et al, ; Hughes & Shaw, ; Roering et al, ).…”

“…In the case of a reverse fault (e.g., a thrust ramp), a frictional surface located ahead of the propagating tip initially deflects the fault plane along the frictional interface, mimicking a ramp‐flat geometry (e.g., Bonanno et al, ). As stress increases, a new fault splay forms and become able to cross the frictional discontinuity when the angle between the two structures reaches a critical value (Bonanno et al, ). Note that until the critical angle is not reached, the propagating fault merely is stopped below the frictional surface (Figure b).…”

Growth of Fault‐Cored Anticlines by Flexural Slip Folding: Analysis by Boundary Element Modeling

“…Again, each of these mechanical models investigates the passive folding of markers in materials of various rheology in response to slip on a fault. On the other hand, boundary element models of Cooke and Pollard (); finite element analyses by Niño et al (), Sanz et al (), and Albertz and Lingrey (); and analogue experiments by Bonanno et al () examined the influence of slip between bedding planes in fault‐related folding. These studies show that the existence a few layers with interface slip can significantly influence the resulting shape of the fold.…”

“…However, as discussed in more detail below, mechanical analyses of fault‐related folding have largely focused on passive folding by slip on faults; the mechanical layers required for buckle folding are absent in many analyses. Notable exceptions are the numerical simulations of Shackleton and Cooke () and Albertz and Lingrey () and analogue experiments of Bonanno et al () that showed that folding of layers above a blind fault is enhanced by allowing flexural slip at layer contacts.…”