Multimodal quantitative segmental analysis of seismicity of the Zhangjiakou-Bohai tectonic belt (North China)

The purpose of this study is to systematically investigate the segmental seismicity features of the Zhangjiakou-Bohai tectonic belt to understand the characteristics of the seismic activity in this tectonic area and identify potential sources of strong earthquake hazard. From the collected seismic data, we first determined the minimum completeness magnitude by combining qualitative and quantitative methods, such as the detection rate function, maximum curvature (MAXC) method, goodness of fit (GFT) method and magnitude-rank method. We used the stochastic declustering method based on the space-time ETAS model to obtain the background seismicity. We then implemented the accelerating moment release (AMR) model, the Ogata-Katsura 1993 (OK1993) model, the moment ratio (MR) model and the Region-Time-Length (RTL) algorithm. Finally, we analyzed the spatial migration of strong earthquakes. The completeness magnitude of the earthquake sequence does not significantly change with time, with the minimum completeness magnitude being 2.0 for the Zhangjiakou-Bohai tectonic zone. The results provided by the aforementioned seismic activity models allow us to detect some differences between sectors of the tectonic belt. The Zhangjiakou and Tangshan segments show a higher level of seismic hazard compared to the others, which have little chance of a strong earthquake occurring (weak release of seismic energy). The b value of the Zhangjiakou segment shows a stepwise downward trend, reflecting the gradual increase of stress accumulation level, and the hazard of moderate-strong earthquakes is increasing. Compared with the Tangshan and Penglai segments, the Zhangjiakou and Beijing sectors have a slightly higher MR index, which means that the rate of earthquake occurrence is increasing and thus the hazard of moderate to strong earthquakes. According to the RTL value, the deviation of seismic activity in the Zhangjiakou and Tangshan segments is relatively high, and there is a possibility of moderate to strong earthquakes in the future. Based on the results obtained from various seismicity models and the migration law of strong earthquakes, we can say that the overall seismic hazard for each sector of the Zhangjiakou-Bohai tectonic chain is low in terms of qualitative analysis. If anything, the Zhangjiakou segment, which is the section with the relatively high seismic hazard level, should require our attention in the future.