Response of Earthquakes to Transient Stresses, in Laboratory and Nature

Citation

Sirorattanakul, Krittanon (2024) Response of Earthquakes to Transient Stresses, in Laboratory and Nature. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2fgg-0m89. https://resolver.caltech.edu/CaltechTHESIS:05202024-162817936

Abstract

Earthquake rates are known to fluctuate with time according to the changing state of stress in the Earth’s crust. Studying the response of earthquakes to transient stresses provides a unique insight into the mechanisms controlling the earthquake nucleation process. Common sources of transient stresses include stress changes from fault slip during large earthquakes, spontaneous slow fault slip, fluid pressure diffusion, seasonal changes of water mass and snowpacks related to hydrological cycles, tidal stresses from changes of gravitational forces of the Sun and the Moon, and anthropogenic fluid injection and extraction related to geoenergy production. In this thesis, we first start in the laboratory-scale fault and conduct friction experiments to enhance our understanding of the underlying friction laws used for modeling earthquakes. We find that the traditional view of Coulomb friction, which postulates that there exists a threshold shear force called “static friction,” below which the frictional interface remains stationary, is incorrect. Our measurements have shown that such an interface is still sliding, albeit with extremely small decaying slip rates down to 10^{−12} m/s. This is consistent with a more recently developed friction law, which describes friction as dependent on slip rate and the state of the interface, e.g., time since the last earthquake. Next, we move beyond the laboratory and study natural faults. In one example, we study the response of earthquakes to transient stress induced by a spontaneous slow fault slip event that preceded the earthquake swarm sequence by approximately half a day. In another example, we study the response of earthquakes to seasonal stress perturbations as a result of seasonal changes in groundwater mass and snowpack between wet and dry seasons, using California as a case study. In both examples, we find that earthquake nucleation is not an instantaneous process. Rather the earthquake rates lag after the stress rates. Such behavior cannot be described by Coulomb friction but can be quantitatively explained by the rate- and state-dependent friction. In the final example, we document bursts of fast propagating swarms of induced earthquakes at the Groningen gas field in the Netherlands. While transient stress must exist to drive the sequence, we cannot explicitly quantify the sources. Overall, our work provides key insights into the earthquake nucleation process, allowing us to better understand how to model the response of earthquakes to transient stress, including earthquakes that are induced by anthropogenic activities related to geoenergy production.

Thesis Files