thermochronometric and textural signatures of earthquakes
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 project - supported by NSF CAREER and SCEC - develops a new approach for identifying and quantifying friction-generated heat from past earthquakes on now exposed fault surfaces in the Wasatch fault zone, Utah, USA with (1) field observations, (2) nano- to microscale fault surface characterization, (3) high-spatial resolution fault rock low-temperature thermochronometry, and (4) novel high-velocity, hematite deformation experiments to simulate laboratory earthquakes. Hematite He, apatite He, and AFT 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.
Publications (denotes * graduate, ** undergraduate, *** postdoctoral mentee) ***Calzolari, G., Ault, A.K., Hirth, G.E., 2020, *McDermott, R.G., 2020, Hematite (U-Th)/He thermochronometry detects asperity flash heating during laboratory earthquakes, Geology, v. 48, p. 509-513, doi: 10.1130/G46965.1. Ault, A.K., 2020, Hematite fault rock thermochronometry and textures inform fault zone processes, invited review article, Journal of Structural Geology, v. 133, p. 104002, doi: 10.1016/j.jsg.2020.1004002. Ault, A.K., **Jensen, J.L., *McDermott, R.G., Shen, F-A., Van Devener, B.R., 2019, Nanoscale evidence for temperature-induced transient rheology and post-seismic fault healing, Geology, v. 47, p. 1203-1207, doi:10.1130/G46317.1 Ault, A.K., Gautheron, C., King, G., 2019, Innovations in (U-Th)/He, fission track, and trapped charge thermochronometry with applications to earthquakes, weathering, surface-mantle connections, and growth and decay of mountains, invited review article for AGU Centennial, Tectonics, v. 38, p. 3705-3739, doi: 10.1029/2018TC005312. |
An exciting dimension of our on-going research, supported by SCEC and NSF CAREER, are deformation experiments in collaboration with Dr. Greg Hirth (Brown University). We use rotary shear experiments, together with microtextural analysis and (U-Th)/He thermochronometry, to characterize the frictional properties and temperatures of experimentally-generated fault materials on thin slip surfaces.
For example, friction experiments at ambient conditions and seismic slip rates (0.032 m/s) reveal hematite has relatively low coefficients of quasi-static and dynamic friction (μ) and deformation yields sintered, nm-scale gouge (Calzolari et al., 2020). These experiments yield >70% He loss from hematite in localized “fault mirror” zones generated during deformation (Calzolari et al., 2020). |