TRAILBLAZER: Leveraging Extreme Environment Experimental Mechanics to Decipher Deep-Focus Earthquake Faulting Mechanisms

About This Grant

This award will fund research to address a grand challenge in the geophysics community: deep-focus earthquakes, which are earthquakes that originate at depths greater than 70km below the Earth’s surface. Although there is no consensus on the processes that cause the sudden release of energy that results in a deep-focus earthquake, there are three agreed-upon mechanisms that could occur individually or together during a deep-focus earthquake event. These mechanisms are 1) the transformation of minerals from one phase to another, 2) the dehydration of rocks, which causes them to become easier to fracture, and 3) the formation of a small molten band caused by thermal heating during shearing. This research project will critically examine each of these mechanisms under the extreme temperatures, pressures, and deformation rates present in the Earth’s mantle. Multiple factors underlie the need for updated earthquake hazard models, including aging infrastructure, continued concentration of population centers, and the fact that supply chain interruptions at one location can have substantial economic impacts well beyond the earthquake-affected region. This project is anticipated to have significant implications for updating earthquake hazard models. Education and outreach efforts will focus on community education, the engagement of citizen scientists, and addressing the scarcity of science education resources in rural counties through the creation of portable teaching toolboxes and science programming for K-12 youth aimed at sparking a passion for science. This research project will advance Pressure-Shear Plate Impact (PSPI) experimentation to achieve the temperatures (up to 2500 K), pressures (>30 GPa), and slip rates (> 1m/s) that occur over the span of depths at which deep-focus earthquakes originate. State-of-the-art PSPI apparatus will be leveraged to generate novel data sets to interrogate prevailing hypotheses as to the cause of deep-focus earthquakes. These data sets include: 1) identifying the onset and defined kinetics of the temperature and pressure-dependent shear-induced phase transformations of silicates (i.e., olivine to wadsleyite or ringwoodite) as a function of deviatoric stress at seismic discontinuity depths; 2) Quantified rheological properties of hydrous peridotite that reveal the relationships between bound water (wt. % H2O), subducted slab thermal parameters, and the emergence of eased fracture embrittlement; 3) An envelope of rate-and-state friction measurements that assess fault weakening (and strengthening) mechanisms under constant and variable normal pressure with the aim of determining whether molten shear band formation is a spontaneous or triggered process. The data captured has strong transformative potential for our understanding of the dynamic processes occurring within the Earth’s mantle, which are currently inferred from sparse surface formations, seismology measurements, or experiments that are unable to simultaneously match subducted slab temperatures, pressures, or slip rates. Anticipated Tranformative Impact: Disaster prevention and mitigation 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.