Correlation between seismic activity and acoustic emission on the basis of in situ monitoring

Abstract. Since April 2023 an in situ experimental campaign has been underway in a granite underground tunnel, which is a dedicated monitoring platform located in Southeast China. Acoustic emission (AE) signals and seismic sequences were recorded simultaneously by installing the AE device together with the seismometer in order to investigate, among other parameters, the b value and the natural-time variance, κ1, of AE time series. In addition, AE and related temporal correlation with incoming seismic events are analysed using an appropriate multi-modal statistical analysis. The results show that AE has a strong correlation with seismic swarms in surrounding areas. The changing trend in AE temporal distribution occurs before that of the earthquake and regularly anticipates a major seismic event by approximately 17 h. The AE bursts indicate that an earthquake is approaching. The dense clusters of AE are closely related to two major earthquakes with Richter magnitudes equal to 3.2 and 2.4. Approaching the earthquake occurrence, the b value shows a downward trend, reaching its minimum value prior to the earthquake, whereas the natural-time variance κ1 rapidly decreases from 0.07 to a minimum value close to zero. Moreover, κ1 occurs earlier than the minimum b value and the AE bursts. Therefore, trends in the b value and the natural-time variance derived from the AE time series can be used as effective earthquake precursors. It is also evident that there is widespread micro-seismic activity in the earthquake preparation zone before the earthquake occurrence. The micro-seismic activity represents the origin of microcracks in the nearby ground surface, resulting in the AE bursts. The results of this paper provide new experimental evidence for the application of fracto-emissions as seismic precursors.