Variations in seismic parameters for the earthquakes during loading and unloading periods in the Three Gorges Reservoir area

Abstract

As the largest water conservancy and hydropower project in China, the Three Gorges Reservoir is a weak seismic activity area before impoundment, but the frequency of earthquakes increases significantly after impoundment. The spatial density scanning method was used to obtain the characteristics of spatio-temporal earthquake distribution in the reservoir area during loading and unloading processes. The results show that the frequencies of earthquakes during the loading and unloading processes were higher than that during the low-water-level operation period, which is well explained by the acoustic emission test results. The seismic b-value, fractal dimension D, and spatial correlation length SCL can be used together to indicate stress criticality. To analyze the impacts of reservoir water loading and unloading on seismicity in the reservoir area, time-scan analyses were performed on the b-value, D-value, and SCL of earthquakes near the Zigui segment and the Badong segment. Previous studies argued that the time-varying characteristics of b-values do not hold predictive significance for earthquakes in the M4.0–6.2 range. However, our study found that the time-varying characteristics of b-values are of predictive significance for earthquakes around M4.0. These seismic parameters decrease significantly before moderate earthquakes but at different rates in different regions.

Vulnerability in the Java northen region in association with earthquake sources of tectonic origin

“…Seismic parameters, a-value, and b-value, can be used to describe respectively the rate of seismicity and the relative proportion of small to large earthquakes of tectonic origin in a region of interest [27,[29][30][31]. In this context, the a-value refers to seismic activity, and the b-value describes tectonic regimes with distinct stresses where a high (low) b-value is associated with a low-stress (high-stress) regime [32][33][34][35].…”