At the boundaries of tectonic plates, deformation evolves with depth, transitioning from rapid earthquakes near the surface to viscous flow at depth. Between these two regimes, transient slow slip events accommodate a significant portion of tectonic movement. However, their dynamics remain poorly understood.
By analyzing these phenomena across several major faults, a team of scientists involving several researchers from CNRS Earth & Universe demonstrated in a recent study that their behavior is primarily controlled by temperature. They thus identified simple laws linking their duration and frequency as a function of depth, common to different tectonic settings.
To conduct this study, the scientists used swarms of low-frequency earthquakes, which act as a proxy for slow slip at depth. Using seismic catalogs covering four tectonic zones (subduction zones and a transform fault), they systematically measured the durations and recurrence intervals of slip episodes.
Statistical analysis of these signals provides access to the temporal dynamics of the processes, allowing these observations to be linked to independent thermal models.
The researchers demonstrated that the duration and frequency of slow slips decrease with depth, while maintaining a constant ratio, implying a nearly uniform average slip velocity. These dynamics occur within a restricted temperature window (~400-550 °C), suggesting a fundamental control of temperature on the mechanics of deep faults.
This result unifies previously disparate observations and opens new avenues to better constrain the physics of transition zones, as well as their links with seismicity and tectonic hazard.
(A-B) The recurrence interval and duration of slow slips decrease with depth.
(C) Their velocity remains nearly constant, intermediate between earthquakes and plate motion.
(D) These dynamics occur within a common thermal window.
© Zaccaria El Yousfi