Abstract
On 8 August 2017, a Ms7.0 earthquake occurred in Jiuzhaigou in the Sichuan Province of China. In this study, we obtained the vertical continuous data recorded at 12 nearby broadband seismometers from April to December 2017, in order to characterize the temporal and spatial variations in the vertical ground motion prior to the onset of the earthquake. Using the self-mutual information method, we determined that from July to August 2017, the self-mutual information value of the vertical ground motion increased at several stations. The spatiotemporal evolution also shows that the region of highest value migrates from south to north toward the earthquake epicenter. Among them, the change of SPA (the station closest to the epicenter) is the most prominent. We believe that this phenomenon is related to the formation of the Jiuzhaigou earthquake. Our work, in combination with other published works, indicates that the Jiuzhaigou earthquake was caused by the continued eastward movement and obstruction of the Qinghai Tibet Plateau by the Sichuan Basin, and the movement of Longmenshan fault is also one of the causes of the earthquake.
Highlights
A Ms7.0 earthquake occurred near Jiuzhaigou in the Sichuan Province of China on 8 August 2017
After smoothing our data to visualize the temporal variations in the selfmutual information values (Figure 4), we examined the spatial variation in self-mutual information values by calculating the monthly mean self-mutual information value at each station using the grid interpolation method (Figure 5)
Based on our self-mutual information results, we infer that the migration of the vibration source from south to north represents the seismic energy gathering before the Ms7.0 Jiuzhaigou earthquake, and that the evolutionary trend of the vertical ground motion in this area reflects the obstruction of material in the middle and lower crust by hard material in the Sichuan Basin, a theory that is supported by the potential decoupling of the middle and lower crust from the upper crust in this region [Xiong and Teng, 2002]
Summary
A Ms7.0 earthquake occurred near Jiuzhaigou in the Sichuan Province of China on 8 August 2017. The seismogenic fault is the northern extension of the Huya fault [Xu et al, 2017, Ji et al, 2017]. This earthquake may be the result of the northeastward extrusion of the lower crust of the Qinghai Tibet Plateau [Li et al, 2017]. By analyzing both the Jiuzhaigou earthquake and the 2008 Wenchuan earthquake via the Coulomb stress method, previous studies proposed that the continuous action of the viscoelastic lower crust increased the Coulomb stress to the point where it eventually resulted in failure and rupture in the Jiuzhaigou area [Cheng et al, 2018]. An alternative theory for the cause of this earthquake involves the accumulation of stress and strain due to the ongoing eastward movement of ISSN (electronic) : 1778-7025 https://comptes- rendus.academie- sciences.fr/geoscience/
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