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.

State of the art of fragility analysis for major building types in China with implications for intensity-PGA relationships

The evaluation of the seismic fragility of buildings is one key task of earthquake safety and loss assessment. Many research reports and papers have been published over the past four decades that deal with the vulnerability of buildings to ground motion caused by earthquakes in China. We scrutinize 69 papers with studies of building damage for magnitude ≥ 4.7 events occurred in densely populated areas starting with the 1975 M7.5 Haicheng earthquake. They represent observations where macroseismic intensities have been determined according to the Chinese Official Seismic Intensity Scale. From these many studies we derive the most representative fragility functions (dependent on intensity) for 4 damage limit states of two most widely distributed building types: masonry and reinforced concrete. We also inspect 18 papers that provide analytical fragility curves (dependent on PGA) for the same damage classes and building categories. Finally, we check the consistency of fragilities as functions of intensity and PGA and derive corresponding relationships between macroseismic intensity and PGA. The intensity-PGA relationship developed in this study is fully compatible with results of previous research.