Fault damage zones—the shattered rock surrounding a major earthquake fault—may contain a hidden record of the largest earthquake that fault can produce. Current methods for estimating the maximum possible earthquake magnitude on a given fault rely on incomplete historical records and painstaking paleoseismology. This project tests whether the type, width, and intensity of damage in the rock around a fault can distinguish earthquakes above roughly magnitude 6.6–6.8 from smaller ones. If so, geologists could read the maximum earthquake size directly from the rock, without needing a full seismic history. If successful, this would provide an independent, deterministic check on a critical input to probabilistic seismic hazard assessment. That assessment directly shapes building codes, insurance rates, and safety planning for critical facilities such as nuclear power plants and dams in seismically active regions. A more reliable estimate of maximum earthquake size could reduce uncertainty in hazard models—potentially lowering the estimated hazard on some faults by showing that rare large earthquakes dominate moment release, meaning fewer moderate but frequent damaging events. This is primarily fundamental science about how earthquake energy dissipates in the crust. The researchers will combine field geology, rock mechanics experiments, and fracture theory to build a roadmap linking outcrop features to earthquake source physics.
View original technical description
Overview: For the past two decades, the PIs have studied the structure of fault damage zones with the intent of understanding how damage zone architecture develops over long term fault evolution and provides feedbacks with the earthquake rupture in the principal slip zone, resulting – along with work of others – in a deep literature regarding damage zone structure, the impact of fault zone damage on effective constitutive behavior and permeability, and scaling laws between slip, fault damage intensity, and fault zone thickness. Much like the debate on the genesis/significance of pseudotachylyte toward the end of the 20th century, leading to insights into earthquake source characteristics from pseudotachylyte-bearing faults, the next step in advancing the state of the art in damage zone science is to make direct connections between outcrop observables and earthquake source characteristics. A fundamental question in our research is whether fault damage zones contain information about Mmax (the maximum earthquake size a fault can host) in terms of type, style, extent, width and degree of damage. We propose to developing criteria to distinguish damage related to earthquake rupture from quasi-static damage accrued over the longer-term fault evolution, and to use these criteria to test the hypothesis that the style and intensity of damage on faults that experience earthquake magnitudes greater than ~Mw6.6 to 6.8 can be clearly distinguished from that on faults experiencing smaller magnitude events. We suggest the difference in damage state can be explained by increased energy dissipation by off fault deformation above a critical moment magnitude threshold, and understanding this relation yields the potential for estimating Mmax for active faults with incomplete historical and paleoseismological records. We propose to conduct a collaborative study utilizing field-based structural geology, cutting edge rock mechanics experiments, and theoretical rock and fracture mechanics to provide a roadmap for identifying uniquely seismic features preserved in damage zones, and to test the overarching hypothesis that Mmax can be estimated by examining the damage zone structure of active strike slip faults. Intellectual Merit: Mmax is a critical component of probabilistic seismic hazard assessment (PSHA) as it limits the maximum size of earthquakes considered in a seismic hazard model. The slip rates of faults are the main driver of hazard, but Mmaxcontrols the upper end of moment release. If Mmax is large, then a significant proportion of the long-term seismic moment release is accommodated by rare large earthquakes. In PSHA, this actually decreases hazard because it results in fewer moderate earthquakes, which also generate strong shaking but have higher recurrence rates. Hence, quantitative information on Mmax is a significant aspect of quantifying hazard to critical facilities. Current approaches for determining Mmax can be strengthened by developing independent criteria that allow for Mmax determination without knowing the full paleoseismic history. This project has the potential for developing an independent, deterministic criterion for Mmax on individual active faults by examining the damage zone structure. Broader Impacts: The Broader Impacts lie in large part in the development of an independent check on Mmax determined for individual faults. If successful, this will have transformative impact on PSHA. This effort is synergistic with the aims of NSF-supported centers like SCEC and dovetails with the recent push to build a near fault observatory in California.Furthermore, this proposal is being submitted between US PIs Ashley Griffith (Ohio State) and Thomas Rockwell (SDSU) and UK PI Thomas Mitchell (UCL) under the NSF/GEO-NERC Dear Colleague letter; therefore, the project will benefit from significant investment from the NERC if selected for funding by the NSF. This project will support multidisciplinary education of two graduate students in the US, all of whom will participate in field work and experiments in both laboratories, as well as bi-weekly Zoom meetings of all project participants. Undergraduate students at OSU, where a thesis forms the capstone requirement of all B.S. degree seekers in Earth Sciences, will participate in experiments and microstructural analysis.
Plain English summaries and category classifications on this site are generated by AI and may not perfectly reflect the original research.
Is something wrong? Let us know