Analysis of Global Positioning System (GPS) time-series data from nearly 100 large earthquakes worldwide has provided evidence for the existence of a precursory phase of fault slip occurring two hours before seismic rupture.
“If it can be confirmed that earthquake nucleation often involves an hours-long precursory phase, and the means can be developed to reliably measure it, a precursor warning could be issued,” writes Roland Bürgmann in a related Perspective. The ability to predict large earthquakes has been a longstanding yet elusive goal. Short-term earthquake prediction – the ability to issue a warning from minutes to months before a quake occurs – relies on a definitive and observable geophysical precursor signal. Previous retrospective studies of several large earthquakes have suggested that a precursory phase of slow aseismic slip can be observed in faults before a mainshock.
However, the relationship between these observations and seismic ruptures is poorly understood as they don’t directly precede an event and occur frequently without being followed by an earthquake. As a result, the existence of a clear precursory signal capable of predicting large earthquakes remains uncertain. Here, Quentin Bletery and Jean-Mathieu Nocquet present a systematic global search for short-term precursory fault slip before large earthquakes. Using global high-rate GPS time series data from 3,026 geodetic stations worldwide, Bletery and Noquet measured fault displacement up to two hours before 90 different magnitude 7 and above earthquakes occurred. Statistical analysis of the data revealed a subtle signal consistent with a period of exponential acceleration of fault slip near the eventual earthquake’s hypocenter beginning roughly two hours before the rupture.
