Distinguished Speaker Huang examines "Physics of Injection-Induced Earthquakes"
Next up in the EES Distinguished Speaker Series is Dr. Yihe Huang from University of Michigan.
"Physics of injection-induced earthquakes unveiled by seismic wave analysis and numerical simulations"
It is well known that fluid injection can induce earthquakes, but how fluid induces earthquakes initially and then contributes to the sequences of earthquakes following afterwards are still puzzling. Fluid pressure is usually considered as the major driving force when injection wells are close to the fault, whereas stress loading due to poroelastic deformation can take over when injection wells are more distant. We tackle three questions related to the physical processes of induced earthquakes: 1) How large is the change of fluid pressure or poroelastic stress? 2) Can fluid migration leave a signature in earthquake characteristics and ground motions? 3) Are earthquakes always a direct response to fluid injection?
Using spectral ratio approaches based on empirical Green’s functions, we show that stress drops of induced earthquakes are indistinguishable from those of tectonic earthquakes in the central US, indicating that most stress released by induced seismicity has been accumulated by tectonic activities and the fluid-induced fault stress change is relatively small compared to the absolute fault stress levels. We also explore the magnitude-frequency distribution (MFD) and spatial-temporal evolution of induced seismicity by improving detections of small earthquakes using single-station waveform template matching. We find significant temporal variations in the MFD with respect to Gutenberg-Richter statistics that suggest temporal changes in deformation patterns and source mechanisms. By forward-modeling the rupture directivity of major induced earthquakes, we show that the 2016 Fairview earthquake that occurred near a high-pressure injection zone ruptured toward injection wells, whereas the 2011 Prague and 2016 Cushing earthquakes ruptured away. Such observations are consistent with numerical simulations with energy-based crack propagation and fluid flow, which suggest that high-pressure injection and low-stress faults can together favor ruptures propagating back to injection wells. We also find through simulations of induced earthquakes that aseismic slip plays an important role in inducing earthquakes besides fluid pressure and poroelastic stress. Small fluid-induced stress perturbations can trigger substantial aseismic slip that may either advance or delay subsequent earthquakes. Finally, our analysis of very small induced earthquakes in an injection experiment in France revealed their low stress drops, supporting the notion that there was tremendous amount of aseismic deformation during the experiment.
Join us for this unique perspective on Injection-induced earthquakes on Friday September, 13, 2019 at 12:30 PM in Room 204 Natural Science Building on the East Lansing Campus.