Deep interactions between faults, earthquakes, creep, and rock fabric: Why do seismicity and fault creep care about rock foliation?
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Vera Schulte-Pelkum
University of Colorado Boulder
- Date & Time
- Location
- Online-only seminar via Microsoft Teams
- Host
- Travis Alongi
- Summary
Faults show a wide range of behaviors in locking and creeping, simple or complex geometries, and patterns of alignment of fault strands and microseismicity. Off-fault deformation and how faults root into a ductile substrate are not well understood. Receiver functions are very sensitive to rock fabric contrasts and can be used to image narrow shear zones even without changes in bulk seismic velocity. They can detect detachment faults, such as the Main Himalayan Thrust, the Appalachian detachment, and the recently proposed Pioneer detachment in the San Andreas-Cascadia transition zone. They can also be used to image near-fault deformation fabric deep into the crust. Results show that fabric strength is amplified in the immediate vicinity (a few kilometers) of faults, with orientations aligned with fault strikes. Fault-parallel fabric continues well below the seismogenic zone. Surprisingly, rock fabric strength near faults correlates with fault creep rate, more strongly so than recently proposed correlations between fault alignment and creep. Another strong correlation is between anisotropy of microseismicity and creep rate. The correlation between these geological time scale (rock fabric) and short term (seismicity and creep) processes suggests that both are controlled by lithology. The depth and orientation resolution offered by fabric imaging opens new avenues of research.