Frequent observations of identical onsets of large and small earthquakes

Every gigantic earthquake begins as a tiny rock failure at almost a point, followed by successive slip of the complex fault system, before radiating strong shaking from a vast rupture area extending over hundreds of kilometres. Whether the growth process of the rupture of a large earthquake is predictable and whether it produces observable signatures different from that of smaller events1–5 are fundamental questions related to the potential for earthquake early warning and probabilistic forecasting. Inspired by a recent discovery that large earthquakes might have seismic waves, and probably rupture processes, that are almost identical to those of smaller events6–8, we show that such similarity characterized by large cross-correlation is a common feature of earthquakes in the Tohoku–Hokkaido subduction zone, Japan. A systematic comparison of 15 years of high-sensitivity seismograph records for approximately 100,000 events reveals 80 extremely similar and 390 very similar pairs of large (moment magnitude M > 4.5) and small (M