Absolute geomagnetic measurement is very important at geomagnetic observatories. It plays a decisive role in data quality control and instrument calibration. As absolute geomagnetic measurements from modern fluxgate theodolite instruments have high precision, usually within 1 arcsec, the measurement results are susceptible to external factors. The operator difference is one of these factors and has become an important consideration that can not be ignored with respect to measurement results. Therefore, an experiment was designed in order to estimate the operator difference. Six fluxgate theodolites were used and six observers who were proficient in absolute measurements were invited to participate. The observers took turns making absolute geomagnetic measurements, and the operator difference between the observers for each instrument was computed by comparing baseline values using statistical methods.

The Absolute Measurement Session during the XIVth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing was held at the Changchun Magnetic Observatory (CNH) September 14-17, 2010. Approximately 50 participants joined in this session. During the session, 27 DI-Flux magnetometers were used to make and compare measurements, and several total field comparison measurements were conducted to look for errors within 4 total field instruments. This session also included absolute measurement training with lectures and practical training, an introduction to INTERMAGNET, and the demonstration of Autodif MKII and DI3

The dependence of the storm-time amplitude on longitude and latitude was analyzed by statistically investigating great magnetic storms observed at different observatories. First, we compared the storm-time ranges observed at Beijing Observatory (BJI) and San Juan Observatory (SJG) to reveal their longitudinal dependence. It was found that the difference between BJI and SJG could be fitted by the 4-order Fourier series approximation, and the storm-time H ranges at dawn were less than those at dusk. Second, we carried out a case study of two typical storms, and analyzed the focused local time when peak storm-time H ranges occurred. The results confirmed the above conclusion. Third, a statistical study was conducted for all magnetic storms observed at the 120°E magnetic chain in eastern China for 1995–2004 to reveal the latitudinal dependence of storm-time ranges. It was found the relationship depended on the activity of analyzed storms and became complicated for giant storms with Dst ≤ −300 nT.

Mining-induced seismicity poses significant safety risks in deep coal mining operations, necessitating advanced monitoring and accurate hazard assessment. Based on 15,584 microseismic events from a coal mine in Gansu, China, in 2024, this study investigates the spatiotemporal characteristics of mining-induced seismicity and its quantitative relationship with excavation disturbances. The methodology integrates Gaussian Mixture Model (GMM) clustering analysis with maximum likelihood estimation of b-value. Key findings include: (1) GMM clustering effectively identifies distinct seismic zones under different stress states, with significant variations in b-values (0.64–0.70). Low b-value zones correspond to high stress concentration and potential for strong events, enabling refined hazard assessment; (2) The time-sliding window analysis reveals the dynamic evolution of the b-value, which exhibits a clear negative correlation with high-energy seismic activity. When the b-value drops sharply to 0.6 or below, the likelihood of high-energy events increases markedly. Notably, 7 out of 8 high-energy seismic events occurred below this threshold. (3) Seismicity migrates with working face advancement, with monthly excavation length positively correlating with seismic energy release, confirming excavation as the primary trigger. This b-value spatiotemporal analysis framework provides scientific basis for early warning and mining optimization in deep coal mines.