Experimental tectonic tremors triggered at subduction zone conditions

The origin of tectonic tremors, low-amplitude and long-duration seismic signals, observed at depth greater than 20-30km at some of the world’s tectonic plate boundaries, remains enigmatic. Here, olivine + antigorite mineral assemblages, containing up to 75 vol.% of the hydrous bearing phase, thought as analogues for dry and water-rich subducting lithologies, were experimentally compressed along pressure-temperature (P-T) paths typical of hot subduction zones. During all experiments, ultrasonic acoustic monitoring of the compression was performed. At PT conditions below 1GPa and 500°C, earthquake-like signals were recorded, with a peak activity at 0.5GPa and 250°, ie. conditions coresponding to the base of the megathrust . Above these PT conditions, spectral analysis (corner frequency, stress drop, duration vs. moment) revealed that the recorded acoustic emissions (AE) signals shared striking similarities with natural tectonic tremors. In particular, stress drops of few kPa and linear moment release vs. duration scalings were observed. While nominally dry experiments confirmed that these tremor-like AEs originated from the viscous deformation of the dry matrix, hydrous mineral bearing experiments demonstrated that experimental tremors could be triggered in bursts at the onset of dehydration reactions, probaly via a mechanism compatible with dehydration stress transfer.