  We analyse the compiled set of precursory data that were reported to be
available in real time before the Ms 7.5 Haicheng earthquake in Feb. 1975 and
the Ms 7.6-7.8 Tangshan earthquake in July 1976. We propose a robust and simple
coarse-graining method consisting in aggregating and counting how all the
anomalies together (geodesy, levelling, geomagnetism, soil resistivity, Earth
currents, gravity, Earth stress, well water radon, well water level) develop as
a function of time. We demonstrate a 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.
Based on a mock real-time prediction experiment, and simulation study, we show
the potential for an early warning system with lead-time of a few days, based
on this methodology of monitoring accelerated rates of anomalies.
