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Investigating the Triggering Mechanism of the 2019 Mw 5.0 Earthquake in the Weiyuan Shale Gas Field, China

Description: 

Understanding the triggering mechanism of damage earthquakes related to hydraulic fracturing (HF) is critical for seismic hazard mitigation, which highly relies on high-resolution earthquake catalogs and detailed production data. To address the triggering mechanism of the largest earthquake (Mw 5.0) in the Weiyuan shale gas field, Sichuan, we conduct an earthquake relocation and template-matching study. We first refine the local 1-D velocity model and absolute earthquake locations using phases recorded by the five closest stations that are within 10 kilometers of the Mw 5.0 event. We then conduct double-difference earthquake relocation to improve the catalog. Our results show that the Mw 5.0 event nucleated at a depth of 4.5 km, which is 1.8 km below the fracking layer. To identify more earthquakes, we conducted template-matching detection using 334 templates in the vicinity of the Mw 5.0 event. We find 40 times more events with the lowest magnitude of M­_L -1.4. We observe plenty of earthquakes on the NE-striking Mw 5.0 fault plane in the depth range of 3.0-4.5 km that occurred 6 months to 1 month before the mainshock. After a quiescent period with no on-fault earthquakes from -30 to -8 days and few earthquakes since -8 days, the Mw 5.0 occurred as a sudden shock. Analysis of earthquake catalog and injection data support our inference that pore pressure increase due to fluid diffusion contributed to the weakening of the fault plane and the Mw 5.0 event is a delayed triggered earthquake. Our study emphasizes the importance of identification of basement faults and monitoring hydraulic fracturing activities to avoid potential destructive earthquakes.

Session: Understanding and Managing Induced Seismicity [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Jinping Zi

Student Presenter: Yes

Invited Presentation: 

Authors