ABSTRACT

Earthquakes generate heat on fault surfaces and exposed fault rocks that provide a temperature record of past earthquakes. Documenting temperatures and textures produced by fossil nano- to micro-earthquakes in seismically active fault zones has the potential to transform our understanding of the role of heat in fault strength during the seismic cycle and our ability to reconstruct the million-year history of earthquakes that refine modern seismic hazard analysis. This project develops a new approach for identifying and quantifying friction-generated heat from past earthquakes on now exposed fault surfaces in the Wasatch fault zone of Utah with field observations, nano- to microscale fault surface characterization, high-spatial resolution fault rock low-temperature thermochronology, and novel high-velocity, hematite deformation experiments to simulate laboratory earthquakes. The research and education components of this CAREER grant advance desired societal outcomes by offering mentoring opportunities at multiple academic levels from middle school through postdoctoral researcher designed to recruit, train, and prepare a diverse STEM (science, technology, engineering and mathematics) workforce. The project will support a female, early career scientist, a postdoctoral fellow, two graduate students, and four undergraduate research assistants. The education plan supported by this award provides field and laboratory education and research experiences for over 300 middle school students, teachers, and their parents in a rural community located in the shadow of the seismically-active Wasatch fault zone. Education activity modules produced during this project will used to engage middle school students elsewhere along the Wasatch front. The education plan will shape and develop middle school students' STEM identities at a critical time in their lives. This is fundamental for shaping future generation of STEM workforce and increases the likelihood that students will engage with STEM courses in high school, college, and graduate school. Natural and experimental fault textures, parameters, and paleotemperatures can be integrated into construction of hazard maps published by the Utah Geological Survey. Education of students, teachers, and parents about faults, earthquakes, and geohazards will enable stakeholders to understand these reports, their surroundings, and the significant seismic hazards they face.

Deciphering the fault damage zone record of microseismicity is critical for understanding in situ physics of processes promoting fault dynamic weakening, earthquake rupture and propagation, recurrence intervals, and earthquake self-similarity. This CAREER grant involves a transdisciplinary research and education plan to document paleotemperatures on 'mirrored'or high gloss, light reflective hematite and silica slip surfaces to understand deformation mechanisms and fault strength evolution during the seismic cycle. These surfaces are hypothesized to preserve transient, elevated temperatures that yield textural and thermochronometric fingerprints of microearthquakes. Natural fault rocks in the Wasatch fault footwall damage zone, UT, are an ideal research and education laboratory and will be compared with hematite surfaces produced in novel rotary-shear experiments. Research phases include: field characterization of mirrored hematite and silica-coated faults; high-velocity, rotary-shear experiments to document hematite friction, temperature, microstructure, and helium (He) loss; nano- to micro-scale characterization of natural and experimental samples with atomic force microscopy, focused ion beam-scanning electron, and transmission electron microscopy; high-spatial resolution, low-temperature thermochronometry using hematite (Uranium-Thorium)/Helium (He), apatite He, and apatite fission-track dating; and synthesis of natural and experimental fault surface observations. Hematite He, apatite He, and apatite fission track thermochronometry strategies employed here reflect new approaches to decipher complex spatial and temporal thermal-resetting signatures. When coupled with microtextures and compared with experimental results, these in situ fault paleotemperatures proxies bear directly on potential hematite and silica fault dynamic weakening mechanisms such as flash heating of asperities. The integrated education plan applies place-based and research-based field and lab learning activities and sustained engagement with role models to facilitate middle school student interest in earthquake science and STEM, and inform an underprepared and underserved population about relevant seismic hazards. The 5-year plan develops and uses these learning modules for 5th-6th grade education along with teacher workshops in a rural community situated in the shadow of the seismically-active Wasatch fault zone. Education activities mirror project research activities to provide students experiences doing real science at a critical age when they are forming their potential STEM identities.

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