On Delayed Triggering of Earthquakes by Anthropogenic Activities
Description:
It is common to observe relatively large earthquakes that occurred after completion of anthropogenic activities. Such delayed triggering poses a significant challenge in hazard assessment, yet its mechanism remains elusive. Here we focus on the Weiyuan shale gas field, Sichuan Basin, where the largest earthquake (Mw 5.0) occurred 3 months after the shut-in of nearby fracking wells. We first construct a high-resolution earthquake catalog, illustrating that the source fault of the 2019 Mw 5.0 earthquake was activated one year ahead. After frackings were completed nearby, the rate of seismicity decreases until the mainshock occurrence. To explore the mechanism of 3-month delay, we then develop a fault model in 2D antiplane shear governed by rate-and-state friction, coupled to pore pressure diffusion. We take into account three past injections at different wells, and inject fluids in three stages into the velocity strengthening (VS) part of the fault. A velocity weakening (VW), seismogenic patch is placed some distance away from the injector. We observe that after injection stops, aseismic slip is able to propagate further from the VS part of the fault into the VW patch, making it more susceptible to earthquake nucleation. Even though the first and second injections failed to rupture the fault, they both contributed to bringing the fault closer to failure. Eventually, the additional stress perturbation from post-injection aseismic slip due to the third injection triggered an earthquake, which occurred about 3 months after injection stopped.
This type of delayed earthquake triggering due to post-injection aseismic slip from multi-stage injection has not been explored before, and we believe it is highly plausible that such an effect is not unique to our study region. It may be a viable mechanism to explain other induced earthquakes that occur sometime after well shut-in. Apart from pore pressure diffusion and poroelastic effects, post-injection aseismic slip should also be taken into account when assessing the hazard of earthquakes trailing well stimulation completion.
Session: Induced Earthquakes: Source Characteristics, Mechanisms, Stress Field Modeling and Hazards [Poster Session]
Type: Poster
Date: 5/1/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Hongfeng
Student Presenter: No
Invited Presentation:
Authors
Hongfeng Yang Presenting Author Corresponding Author hyang@cuhk.edu.hk Chinese University of Hong Kong |
Jinping Zi zijinping@link.cuhk.edu.hk Chinese University of Hong Kong |
Yuyun Yang yuyunyang@cuhk.edu.hk Chinese University of Hong Kong |
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On Delayed Triggering of Earthquakes by Anthropogenic Activities
Session
Induced Earthquakes: Source Characteristics, Mechanisms, Stress Field Modeling and Hazards