Growing seismicity in the Sichuan Basin and its association with industrial activities

Abstract

In the Sichuan Basin, seismic activity has been low historically, but in the past few decades, a series of moderate to strong earthquakes have occurred. Especially since 2015, earthquake activity has seen an unprecedented continuous growth trend, and the magnitude of events is increasing. Following the M5.7 Xingwen earthquake on 18 Dec. 2018, which was suggested to be induced by shale gas hydraulic fracturing, a swarm of earthquakes with a maximum magnitude up to M6.0 struck Changning and the surrounding counties. Questions arose about the possible involvement of industrial actions in these destructive events. In fact, underground fluid injection in salt mine fields has been occurring in the Sichuan Basin for more than 70 years. Disposal of wastewater in natural gas fields has also continued for about 40 years. Since 2008, injection for shale gas development in the southern Sichuan Basin has increased rapidly. The possible link between the increasing seismicity and increasing injection activity is an important issue. Although surrounded by seismically active zones to the southwest and northwest, the Sichuan Basin is a rather stable region with a wide range of geological settings. First, we present a brief review of earthquakes of magnitude 5 or higher since 1600 to obtain the long-term event rate and explore the possible link between the rapidly increasing trend of seismic activity and industrial injection activities in recent decades. Second, based on a review of previous research results, combined with the latest data, we describe a comprehensive analysis of the characteristics and occurrence conditions of natural and injection-induced major seismic clusters in the Sichuan Basin since 1700. Finally, we list some conclusions and insights, which provide a better understanding of why damaging events occur so that they can either be avoided or mitigated, point out scientific questions that need urgent research, and propose a general framework based on geomechanics for assessment and management of earthquake-related risks.

Source Parameters of Three Moderate Size Earthquakes in Weiyuan, China, and Their Relations to Shale Gas Hydraulic Fracturing

“…All earthquakes are within 2 km to injection wells, which suggest that the earthquakes are very likely to be induced by injection activities. Similar to the 2018 Xingwen earthquake, W1 and W3 are probably nucleated within a zone of elevated pore pressure near injection wells and rupture unidirectionally to the northeast beyond the zone (Lei et al, 2020).…”

Toward Retrieving Distributed Aquifer Hydraulic Parameters From Distributed Strain Sensing

“…A better understanding of the spatial distribution of hydraulic parameters can facilitate more manageable and optimized operations for these utilizations (Miller et al., 2017). Moreover, the parameters are essential for understanding the scale of hydromechanical responses and its role in fluid injection induced seismicity (Guglielmi et al., 2020; Jiang et al., 2020; Keranen et al., 2014; Lei et al., 2020; Shirzaei et al., 2016; Verdon et al., 2015). Hydrogeologists have long pursued an understanding of the spatial structure of hydraulic parameters in aquifer formation.…”

Induced Earthquakes Before and After Cessation of Long‐Term Injections in Rongchang Gas Field

“…The Sichuan Basin provided typical cases, in which both long‐term and short‐term injections have caused noticeable (“felt”) induced seismicity, including some destructive earthquakes. Some large earthquakes, such as the M 5.7 (in this article M indicates M L for events of M L < 5 and M S for events of Ms ≥ 5) earthquake on 18 December 2018 induced by shale gas hydraulic fracturing (HF) (Lei et al, 2019a), the M 6.0 earthquake on 17 July 2019 (possibly induced by long‐term injection for salt production) (Lei et al, 2019b), and several earthquakes of M 4.3 to M 5.4 induced by shale gas HF at the Weiyuan‐Rongxian shale gas site (Lei et al, 2020), caused more than 200 casualties including more than 10 deaths and major economic losses. These cases challenge safety implementation measures of related industries and provide opportunities for research on induced earthquakes.…”