LAUSR

Earthquake early warning would be improved if the final size of an ongoing earthquake could be predicted early in the rupture process. Previous research relies largely on parameters derived from seismic waveforms, resulting in widely varied estimates of how much of the rupture must be complete before final sizes can be predicted. We demonstrate here that incorporating prior information on along‐strike variation in source fault structural maturity helps improve constraints on the earthquake's final size. Using surface slip profiles from 26 large continental earthquakes worldwide, we derive a generic empirical relation between earthquake slip, rupture length, and along‐strike variability in source fault maturity. Using this equation, we fit successive slip profiles developing during each earthquake and find that, on average, we predict the final length and magnitude of an earthquake once it has reached ~20% of its total length. Our findings thus demonstrate a clear determinism in the rupture process.