Biomarker Thermal Maturity Reveals Localized Temperature Rise From Paleoseismic Slip Along the Punchbowl Fault, CA, USA

Heather M. Savage, & Pratigya J. Polissar

Published July 8, 2019, SCEC Contribution #9984

The Punchbowl Fault, California, USA, is an example of a simple fault zone that has a relatively narrow fault core with further slip localization to principal slip zones. We sampled the principal slip zone, fault core, and wall rocks and conducted hydrous pyrolysis experiments to analyze biomarker thermal maturity within the Punchbowl Fault. Using biomarker maturity as a proxy for temperature rise, we show that the existing principal slip zone experienced greater temperature rise than the surrounding fault core and wall rock, and therefore, we infer that earthquake slip localized along this layer. Furthermore, evidence of slight thermal maturity within the ultracataclasite suggests that the fault core is made up at least in part of reworked former principal slip zones. Using a wide range of possible layer thicknesses, we find that the maximum temperature range during a single earthquake could have varied from ~460 to 1,060 °C at 1‐m/s slip velocity. However, not all samples from within the principal slip zone show a temperature rise, indicating that layer thickness, slip, or shear stress varied during slip. Our temperature estimate also allows us to constrain the frictional energy dissipated during the earthquake to 2.2–25 MJ/m2. Our study demonstrates that localized slip structures can be directly linked to seismicity and that small changes in earthquake or fault parameters can lead to changes in temperature (and likely fault strength) at small scales.

Citation
Savage, H. M., & Polissar, P. J. (2019). Biomarker Thermal Maturity Reveals Localized Temperature Rise From Paleoseismic Slip Along the Punchbowl Fault, CA, USA. Geochemistry, Geophysics, Geosystems,. doi: 10.1029/2019GC008225.