Radiofluorescence as a tool to estimate the degree of friction-induced heat caused by co-seismic slip

Sufficient temperature rise during frictional heating is a key parameter controlling whether luminescence dating of fault gouges can determine the timing of past earthquakes. Regardless, the true temperatures induced in the rock during a co-seismic slip event are often unknown. This significantly hampers the accuracy of luminescence age results from fault gouges. Laboratory-controlled friction experiments can adequately simulate different friction scenarios by modulating normal stress and slip velocity and then recording induced temperatures using thermocouples [1] or an infrared camera [2]. However, monitoring those events in nature is highly impractical for past events.

Systematic luminescence studies on ultraviolet (UV) radiofluorescence (RF) of quartz reported a strong correlation between heating and subsequently recorded UV-RF signaldynamics [3,4].

Here, we explore the potential of UV-RF to shed light on the extent of friction-induced temperature in quartz-bearing host rocks. In our experiments, we tested one sediment quartz sample with a known luminescence characteristic and a polymineral sample from the North Tehran Fault. For one part of each sample, we first recorded a UV-RF temperature profile after heating subsamples in batches from 30 ºC to 575 ºC in increments of 25 ºC. The other (untreated) part was then subjected to frictional heating in the laboratory under a normal stress of 12 MPa and a slip velocity of 5 cm/s using a rotary shear apparatus. During the experiment, the frictional heat was recorded using an infrared camera. We then measured the UV-RF signal and projected the results onto the signal-preheat profile to estimate the (unknown) frictional heat temperature.

Although our study is preliminary at this stage, we could calculate realistic friction-induced temperatures for the quartz sample. In contrast, the UV-RF signals of the polymineral sample will require additional experiments. We will present the experimental design and initial results, and discuss the challenges and the potential of our approach for tracking the temperature levels generated by earthquakes.

References

[1] Kim, J.H., Ree, J.-H., Choi, J.-H., Chauhan, N., Hirose, T., Kitamura, M., 2019. Experimental investigations on dating the last earthquake event using OSL signals of quartz from fault gouges. Tectonophysics 769, 228191. https://doi.org/10.1016/j.tecto.2019.228191

[2] Heydari, M., Kreutzer. S., Hung, C.C., Martin, L., Ghassemi, M.R., Tsukamoto, S., Niemeijer, A., under review, Scientific Reports. Unveiling Earthquakes: Thermoluminescence Signal Resetting of a Natural Polymineral Sample in Laboratory-Produced Fault Gouge

[3] Friedrich, J., Pagonis, V., Chen, R., Kreutzer, S., and Schmidt, C.: Quartz radiofluorescence: a modelling approach, Journal of Luminescence, 186, 318–325, https://doi.org/10.1016/j.jlumin.2017.02.039, 2017a.

[4] Friedrich, J., Fasoli, M., Kreutzer, S., and Schmidt, C.: The basic principles of quartz radiofluorescence dynamics in the UV - analytical, numerical and experimental results, Journal of Luminescence, 192, 940–948, https://doi.org/10.1016/j.jlumin.2017.08.012, 2017b.