As Roland Burgmann articulates in a connected Perspective, "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." Predicting major earthquakes has remained an elusive achievement, despite decades of scientific research. The key lies in detecting a definitive, observable geophysical precursor signal that would enable accurate short-term earthquake prediction.
Earlier studies, which retrospectively analyzed large earthquakes, have postulated that slow, aseismic slip may occur in fault lines ahead of the main shock. However, the link between these observations and seismic ruptures is not well-defined. Moreover, these precursory activities often don't immediately precede an event and frequently occur without triggering an earthquake. This uncertainty has clouded the existence of an unambiguous, precursory signal for predicting large-scale seismic events.
In this study, Quentin Bletery and Jean-Mathieu Nocquet attempted a global, systematic search for this elusive short-term precursory fault slip. Using high-rate GPS data gathered from 3,026 geodetic stations across the globe, they measured fault displacement up to two hours before 90 different earthquakes, each with a magnitude of 7 or above.
The pair's statistical analysis unveiled a subtle signal, indicating a period of exponential acceleration in fault slip near the epicenter of the impending earthquake. This acceleration began roughly two hours before the seismic rupture.
The authors interpret their findings to suggest that a significant proportion of large earthquakes may initiate with a detectable phase of slip, or that the detected observations represent the tail-end of an extensive, more challenging to measure process of precursory slip.
While their findings hint at a precursory signal before large earthquakes, Bletery and Nocquet note a significant limitation. Existing earthquake monitoring instruments lack the coverage and precision needed to identify or monitor for precursory slip at an individual earthquake's scale.
Burgmann further notes, "Although the results of Bletery and Nocquet suggest that there may indeed be an hours-long precursory phase, it is not clear whether such slow-slip accelerations are distinctly associated with large earthquakes or whether they could ever be measured for individual events with the accuracy needed to provide a useful warning."
Research Report:The precursory phase of large earthquakes
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