SCEC Award Number 24119 View PDF
Proposal Category Collaborative Research Project (Multiple Investigators / Institutions)
Proposal Title Experimental constraints on shallow earthquake rupture propagation in altered serpentinite gouge: Implications for northern CA including the Bartlett Springs fault
Investigator(s)
Name Organization
Monica Barbery Brown University Greg Hirth Brown University Alexis Ault Utah State University Srisharan Shreedharan Utah State University
SCEC Milestones B1-1, B3-3, D1-1 SCEC Groups FARM, CEM, Geology
Report Due Date 03/15/2025 Date Report Submitted 03/14/2025
Project Abstract
 Creep controls the stress on faults and influences how faults slip throughout the earthquake cycle. The San Andreas fault system, including the Bartlett Springs fault, in northern CA comprises creeping faults with altered serpentinite. Can large earthquakes nucleate in and/or propagate through this fault material? We used comparative direct shear and rotary shear deformation experiments to characterize the frictional behavior and assess the role of fabric development from a high-spatial resolution sample transect across exhumed Bartlett Springs fault gouge. New X-ray diffraction data indicate samples are composed of mixtures of serpentine minerals, chlorite, quartz, talc, kaolinite, and smectite. Spatially heterogeneous mineralogy governs the frictional behavior of reconstituted gouges the BSF. The presence of alteration phases including talc and smectite locally within gouge contribute to its weakness (u = 0.15-0.2) and low healing rates. Ultralow healing rates from a direct shear apparatus and lower healing rates with fabric development generated during the Tullis rotary shear experiments are consistent with the dominance of creep along the Bartlett Springs fault. Instron experiments suggest that the development of fabric increases the frictional stability. Our results imply that earthquakes would not nucleate in altered, talc and smectite-rich patches in Bartlett Springs fault.
Intellectual Merit Creep impacts the full earthquake cycle and may release some fault earthquake moment budget. Dynamic rupture models predict earthquakes can occur along creeping faults but the magnitude depends on fault geometry and fault friction. The San Andreas fault system in northern CA is dominated by creeping faults with altered serpentinite, and an outstanding question that aligns with SCEC research themes and milestones is the extent to which earthquakes nucleate and propagate into this material. Deformation experiments, including healing protocols, are required to simulate rupture propagation through creeping materials and assess the role of fabric development on earthquake frictional behavior.
Broader Impacts This project was led by and supported newer SCEC investigators (Barbery, Shreedharan) in partnership with established SCEC PIs (Hirth, Ault) with the combined expertise necessary to accomplish research objectives and address SCEC milestones. Barbery, Shreedharan, Hirth, and Ault mentored USU PhD student Armstrong on experiments on a direct shear and rotary shear apparatuses. This project supported undergraduate researchers at Brown and USU (Ainsley Macdonald, Brandt Bechtel). To date, these data have been presented at three conferences including SCEC, Gordon Research Conference on Rock Deformation, and AGU.
Project Participants Monica Barbery, Greg Hirth, Alexis Ault, Srisharan Shreedharan, Emma Armstrong (USU PhD student), Ainsley MacDonald (USU undergraduate student), Brandt Bechtel (Brown REU summer intern)
Exemplary Figure Figure 3. (A) Coefficient of friction as a function of shear displacement for DSA for each sample. (B) Frictional healing as a function of hold time for SHS experiments on sample EA23-17 the DSA and TRS. DSA experiments include up to 1,000,000 s hold time; TRS experiments include 0.5-1 m of initial slip with one order of magnitude faster slides after 1 m of slip. (C) DSA data for sample EA23-17 for comparison with (D) results from the TRS showing similar steady-state ยต at saturated conditions and 10 MPa normal stress. Modified from Armstrong et al. (in prep).
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