By combining the seismogenic environment, seismic recurrence periods of strong historical earthquakes, precise locations of small–moderate earthquakes, and Coulomb stress changes of moderate–strong earthquakes, we analyze the potential locking status of a seismically quiet segment of Xianshuihe fault between Daofu County and Kangding City (SDK). The interseismic surface velocities between 1999 and 2017 are obtained from updated global positioning system (GPS) observations in this region. After removing the post-seismic relaxation effect caused by the 2008 M_w 7.9 Wenchuan earthquake that occurred around the fault segment, the observed velocities reveal a pronounced symmetric slip pattern along the SDK trace. The far field slip rate is 7.8 ± 0.4 mm/a, and the fault SDK is confirmed to be in an interseismic silent phase. The optimal locking depth is estimated at 7 km, which is perfectly distributed on the upper edge of the relocated hypocenters. A moment deficit analysis shows cumulative seismic moment between 1955 and 2018, corresponding to an M_w 6.6 event. Finally, based on a viscoelastic deformation model, we find that moderate–strong earthquakes in the surrounding area increase the Coulomb stress level by up to 2 bars on the SDK, significantly enhancing the future seismic potential.

Unprecedented levels of seismicity have been seen in southern Sichuan, China, since the large‐scale exploitation of shale gas. Fluid and pore pressure transported through hydrological channel are thought as pivotal elements in the induction of earthquakes. Our high‐resolution tomography results reveal two inclined seismic anomalies featured by low V _s and high V _p / V _s at different depth range. The deeper anomaly extends 15 km from NE to SE and connects the well g 048 from 3 km depth to the vicinity of the Ms 4.7 Gongxian earthquake 5.4 km deep, which is hinted to be a hydrological channel inferred from the high fluid overpressure of 28 Mpa calculated from focal mechanism solution. The injection operation of multiple shale gas wells along the channel may potentially accumulate the pore pressure and cause the fault near the end of the channel to reach critical stress state through various mechanisms.

Frequency‐dependent anelastic attenuation is a fact that must be considered when inverting seismic data. The shallow attenuation characteristics of large sedimentary basins with frequent earthquakes in mainland China are still unclear, which hinders the study of strong ground motion. Borehole seismometers distributed in these areas provide information on shallow structures. In this study, the direct and surface‐reflected phases in local earthquake borehole seismograms were extracted to calculate the average S wave anelastic attenuation of shallow sediments in mainland China. Relying on the seismograms recorded by 103 borehole stations, the attenuation values and lithologies of the shallow sediments above the borehole seismometers were estimated by applying a multi‐time window analysis method. We suggested that the values generally decrease from 0.04–0.50 at 1 Hz to 0.01–0.05 at 10 Hz. We obtained the empirical relationships among attenuation, velocity, and depth and found that the dominant mechanisms for attenuation above and below a depth of 400 m could be different due to sediment compositions and scales. Certain borehole depths and corresponding V_s values were corrected by analyzing the time difference variation and the distinction.

SUMMARY: The Groningen gas field located in the northern Netherlands is the largest gas field in Europe. Many induced earthquakes have occurred since the gas extraction commenced in the 1960s, especially in the last two decades, which have caused concerning social and economic problems. To better quantify the seismic hazards caused by the induced earthquakes, the near surface attenuation in the Groningen area needs to be characterized from actual earthquakes. The spectral ratio method based on multiwindow analysis has proven to be a powerful tool to estimate the S-wave attenuation parameters of shallow sediments. In this study, waveforms from earthquake events recorded by the dense network of 70 boreholes, each of which is equipped with four geophones are used to estimate the S-wave attenuation parameters of shallow sediments. There are strong lateral variations in the near-surface attenuation, which is structurally similar to the S-wave model from a previous study in the same area. Besides, the calculated $Q_S^{ - 1}$ values are inversely proportional to the frequency and depth. The averaged ${\rm{\ }}Q_S^{ - 1}$ values for depths between 0–150 m and 0–200 m are close to those of the soft soil Sendai basin in Japan. The $Q_S^{ - 1}$ values from this study have been used to model a surface peak ground acceleration (PGA) map. As expected, both near surface $Q_S^{ - 1}$ values and source mechanism have a profound effect on the modelled PGA.