An Improved Estimation of Stress Drop and its Application on Induced Earthquakes in the Weiyuan Shale Gas Field in China
Description:
The hydraulic fracturing activities in the Weiyuan Shale Gas Field of Sichuan Province, southwestern China, have triggered an increasing amount of earthquake activities in the past 8 years compared to the silent historical record, accompanied by a deadly ML4.9 earthquake in 2019 and multiple ML4.0+ earthquakes afterward. How these earthquakes are related to injection activities is still under debate. Earthquake stress drops have been found to vary spatially and temporally from anthropogenic activities, therefore in this study we aim at estimating the stress drops in the Weiyuan region to reveal the triggering mechanisms of the large earthquakes and inspect the seismic hazard from shale gas exploration.
We include 28,000 earthquakes from Feb. 2019 (after the ML4.9 earthquake) to Aug. 2020. Most are located at shale layer depths (2-4km over space). We propose an improved spectral-decomposition-based approach to estimate their stress drops: the method does not assume stress drop dependence earthquake scale, and significantly mitigate stress drop underestimation. The median stress drop of the Weiyuan earthquakes is 3.08MPa, and stress drops show strong spatial heterogeneity. Based on Mohr-Coulomb failure law, we calculate pore pressures of five ML>4 earthquake from their stress drop values. The results indicate that the Molin fault ruptured by the deadly ML4.9 is near hydrostatic; in the nearby injection zone, other faults of ML>4 earthquakes show over-pressure. These estimates agree with observations that the ML4.9 are missing aftershocks while others do not. Our results show that stress drop can help understand the mechanisms of large induced earthquakes.
Session: Earthquake Source Parameters: Theory, Observations and Interpretations [Poster]
Type: Poster
Date: 4/18/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Jinping Zi
Student Presenter: No
Invited Presentation:
Authors
Jiewen Zhang Corresponding Author jwzhang@cuhk.edu.hk Chinese University of Hong Kong |
Hongfeng Yang hyang@cuhk.edu.hk Chinese University of Hong Kong |
Jinping Zi Presenting Author zijinping@link.cuhk.edu.hk Chinese University of Hong Kong |
Jinrong Su sujr0816@163.com Sichuan Earthquake Administration |
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An Improved Estimation of Stress Drop and its Application on Induced Earthquakes in the Weiyuan Shale Gas Field in China
Category
Earthquake Source Parameters: Theory, Observations and Interpretations