Observations of Fault Growth Under Elevated Fluid Pressure Using Dynamic Microtomography

点击翻译按钮获取中文摘要

Sudden motions of a tectonic fault such as the San Andreas fault cause earthquakes. Better seismic risk assessment requires quantitative knowledge of fault distribution and propagation. The discovery of slow slip events, those that occur over hours to months instead of seconds, at convergent plate boundaries, like in the Pacific Northwest, provides new opportunities to study the mechanics of earthquakes and other fault instabilities. Seismic observations link slow slip events to high fluid pressure within the fault zones but how this works mechanically is still unclear. Recent studies in the lab that emulate these conditions show that increasing pore pressure slow down fault growth. This project looks to advance these experiments to improve our understanding of the mechanics of slow faulting under high pore pressure. The work has broader impacts on our understanding of seismic hazards at coastal plate boundaries as well as other areas that see this type of complex faulting. The researcher will also provide a research experience for an undergraduate, and conduct outreach to a nearby high school to bring students into a scientific lab. The project supports a postdoctoral fellow and a graduate student.The researchers hypothesize that dilatant hardening at crack tip can cause deformation to migrate, which results in delocalized fracturing and slow fault propagation. To test this hypothesis, the work enables deformation experiments using an X-ray transparent deformation apparatus to record the real-time fault growth. The state-of-the-art dynamic microtomography imaging will elucidate the fault nucleation process and growth pattern in a deforming rock at in-situ conditions. They will also incorporate dilatancy hardening into the damage model to simulate the effect of pore pressure on fault propagation. Comparison of the 3-D microstructure generated by numerical simulations and the time-lapse tomography images will provide new insights into deformation mechanisms. The goal is to build a better understanding of the mechanics of slow fault growth, and thus provide the critical link between the geophysical observations and the stress states of a megathrust fault during the interseismic period of an earthquake cycle.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.