Revisiting the Predictability of the Haicheng and Tangshan Earthquakes

We analyze a set of precursory data measured before but compiled in retrospect of the MS7.5 Haicheng earthquake in February 1975 and the MS7.6–7.8 Tangshan earthquake in July 1976. We propose a robust and simple coarse-graining method that aggregates and counts how all the anomalies together (levelling, geomagnetism, soil resistivity, earth currents, gravity, earth stress, well water radon, well water level) develop as a function of time. We demonstrate strong evidence for the existence of an acceleration of the number of anomalies leading up to the major Haicheng and Tangshan earthquakes. In particular for the Tangshan earthquake, the frequency of occurrence of anomalies is found to be well described by the log-periodic power law singularity (LPPLS) model, previously proposed for the prediction of engineering failures and later adapted to the prediction of financial crashes. Using a mock real-time prediction experiment and simulation study, based on this methodology of monitoring accelerated rates of physical anomalies measured at the surface, we show the potential for an early warning system with a lead time of a few days.

Stress-Related Pre-Seismic Water Radon Concentration Variations in the Panjin Observation Well, China (1994–2020)

Continuous observation data from a period of 26 years show that water radon concentrations in the Panjin observation well document pre-seismic anomalies prior to earthquakes of 4.8 ≤ M ≤ 7 within a radius of 300 km. Among these earthquakes, two distinct groups with different water radon concentration anomalies and anomaly mechanisms are apparent. The abnormal characteristics of water radon concentrations clearly reflect the processes of stress change, while Cl− concentration, Ca2+ concentration, Mg2+ concentration, and escaping gas flow only document part of these processes. According to Global Positioning System main strain rate fields and area strain rate fields, the change in anomalous behavior coincides with the 2011 Great Tohoku M 9.1 earthquake. This event caused the stress state of the study area, located in eastern China, to change from a relative compressive stress state to a tensile state, and may be the main reason for the change in the precursory characteristics of water radon concentrations (from increasing to decreasing prior to earthquakes). Regardless, water radon concentration in the well remains a good pre-seismic indicator for earthquakes of M ≥ 4.8. In the near future (∼50–100 years), water radon anomalies in the Panjin observation well prior to earthquakes of M ≥ 4.8 will most likely manifest as a V-shaped concentration change. Helium and neon isotopic compositions of gas samples from the Panjin observation well show that the present relatively high levels of water radon concentrations are normal and not an earthquake precursor.