Do slickenfibers record episodic tremor and slow slip?

The earthquake cycle encompasses a variety of seismic processes that are only partially understood by geologists. For example, many large, earthquake-producing faults around the world also exhibit persistent episodes of seismic tremor (shaking that is only perceptible with modern instruments) accompanying slow slip (at rates of millimeters per year rather than the meters per second rates typical of earthquakes).

This process, known as “episodic tremor and slow slip”, has been proposed to be a potential precursory phenomenon that may forecast larger earthquake ruptures. Leveraging this forecasting potential, however, requires determining the physical mechanisms underlying episodic tremor and slow slip, which is hindered by the lack of a definitive geologic record.

This research will test the validity of a recently proposed geologic record of episodic tremor and slow slip: quartz veins that form incrementally following micro-slip events in earthquake-producing faults. This work will quantify the time scales of vein formation via hydrothermal experiments and assess their compatibility with those of the recurrence of episodic tremor and slow slip observed in active faults.

Although much of the formation of incrementally developed quartz slickenfibers is consistent with seismological observations of episodic tremor and slow slip (depth, presence of fluids, stress drops, etc), a critical question remains unanswered: are the time scales of slickenfiber formation compatible with seismologically observed repeat times? For this to be true, quartz cements delineating microslip increments in slickenfibers must precipitate over time scales from 3 months to ~2-years depending on tectonic setting.

Given typical fracture opening increments observed in slickenfibers, this conceptual model implies quartz precipitation rates of more than 10 μm / year. These rates are several orders of magnitude faster than those predicted by current kinetic-rate models. Recent work has argued that coseismic decreases in pore-fluid pressure may stimulate transient increases in quartz growth rates, allowing slickenfiber formation over time scales consistent with the recurrence of episodic tremor and slow slip.

To test this hypothesis, this research will utilize a novel approach that allows accurate detection of precipitation rates as small as ~3 μm / year in hydrothermal experiments simulating large coseismic decreases in fluid pressure. Critically, these experiments will be conducted at temperature and pressure conditions consistent with the crustal depths where episodic tremor and slow slip occurs.

Thus, the proposed work will be able to unequivocally determine if the time scales of slickenfiber formation are compatible with those of episodic tremor and slow slip, regardless of how much quartz is grown over the course of the experiments.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.