How effective is effective stress? The evolution of the effective stress law through the brittle-ductile transition

Rabinowitz Hannah S, New York NY

Investigators

Abstract

Dr. Hannah Rabinowitz has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education activities at Brown University. The research project focuses on carrying out deformation experiments to characterize the stress regime in the zone where large earthquakes originate. Earthquakes occur in the Earth's crust where deformation is controlled by brittle fracture and frictional sliding. This brittle portion of the crust is underlain by ductilely flowing material, and the depth to the ductile transition controls how large an earthquake can become. Describing deformation at brittle-ductile transition is essential to the understanding of the nucleation processes that initiate large, societally damaging earthquakes. For the education plan, Dr. Rabinowitz teaches at multiple levels conducting hands-on labs with elementary school children in Providence, RI; leading a seminar course at Brown University; and mentoring an undergraduate student to conduct microstructural analyses as part of a senior thesis. This project addresses the evolution of crustal strength through the brittle-ductile transition (BDT). The combination of the mechanical and detailed microstructural analyses provides new insight into the evolution of the effective stress law through the BDT and the microstructural mechanisms that control the transition in deformation style at the base of the seismogenic zone. Deformation experiments will be conducted to characterize the BDT in the context of a changing effective stress. Experiments on quartz with water pore fluid at pressure and temperature conditions spanning the BDT will allow for the assessment of the conditions at which the effective stress law controls rock strength. Furthermore, experiments on copper with argon gas pore fluid will allow for the isolation of the mechanical effects of pore fluid pressure without the weakening that is expected in quartz in the presence of water. Both 2D and 3D microstructures will be analyzed to determine how the mechanical evolution through the BDT is related to an evolving porosity structure. 2D imaging will be accomplished using traditional techniques such as optical microscopy and scanning electron microscopy (SEM). 3D imaging will be conducted using X-ray microtomography at the University of Maryland. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.