The 2017 Mw 6.5 Jiuzhaigou earthquake occurred at the southeastern boundary of the Bayankala block in Tibetan Plateau. Here we investigate the spatial and temporal seismicity rate changes in the Jiuzhaigou region using the finite‐source epidemic‐type aftershock sequence model and stochastic declustering method. The background probabilities of all events are obtained, and the cumulative background seismicity is extracted and fitted by a linear function. Following from this, we argue that there was a decrease of background seismicity in Jiuzhaigou region immediately after the occurrence of the 2008 Mw 7.9 Wenchuan earthquake. On the other hand, we also calculate the static and viscoelastic stress changes in the area around the hypocenter of the Jiuzhaigou earthquake induced by the Wenchuan earthquake. Although opposite results are resolved by previous studies, we infer a negative Coulomb failure stress change under reasonable assumptions of parameters for this case. Combining these two observed empirical relationships, we conclude that the 2017 Jiuzhaigou earthquake is delayed by the Wenchuan earthquake and the former event possibly results from the southeastward movement of the Bayankala block, which in turn arises from the collision of Indian‐Australian Plate and the Eurasian Plate. These findings indicate that Bayankala block and its adjacent tectonic faults are still in the highly active seismic period that started in the 1990s.

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The Ms 6.0 earthquake in Changning, Sichuan, China, on 17 June 2019 was the largest recorded earthquake in the stable Sichuan basin. It occurred in a complicated region with salt mining and shale gas production. Whether this earthquake is induced raises concerns among the public and the scientific community. Furthermore, the relation between this earthquake and nearby industrial activities has also been of great interest. To address these questions, we estimated the nonstationary background seismicity rate and inverted for spatiotemporal stress changes. The results show that the background rate dramatically increased after hydraulic fracturing (HF) and remained at a high level until the present. Starting in 2005, the study region experienced an accelerating stress increase, and the rates of cumulative modified Coulomb stress changes were approximately 0.11  MPa/yr from January 2005 to January 2015 and 0.24  MPa/yr from January 2015 to December 2018. The 2019 Changning earthquake produced a stress step of 0.32 MPa. A clear difference between seismicity induced by salt mine injection and by HF is documented. Our results suggest that the Changning sequence might have been induced by long-term injection for salt production. Furthermore, the seismicity-stress inversion method provides a tool for using seismicity rate changes as a stress meter to monitor human-induced seismicity.

This paper presents a new adaptive random weighting cubature Kalman filtering method for nonlinear state estimation. This method adopts the concept of random weighting to address the problem that the cubature Kalman filter (CKF) performance is sensitive to system noise. It establishes random weighting theories to estimate system noise statistics and predicted state and measurement together with their associated covariances. Subsequently, it adaptively adjusts the weights of cubature points based on the random weighting estimations to improve the prediction accuracy, thus restraining the disturbances of system noises on state estimation. Simulations and comparison analysis demonstrate the improved performance of the proposed method for nonlinear state estimation.