Based on a systematic global analysis of GPS time-series data from nearly 100 large earthquakes, researchers have identified the presence of a precursory phase of fault slip that typically takes place approximately two hours before the occurrence of seismic rupture, which is proof that GPS data could predict large earthquakes hours in advance.
In a related Perspective article, Roland Bürgmann, Professor of Earth and Planetary Science, in the Department of Earth and Planetary Science at the University of California, Berkeley, highlights the potential significance of this discovery. If further studies can confirm that many earthquakes involve a prolonged precursory phase lasting several hours, and reliable measurement methods can be developed, there may be a possibility of issuing precursor warnings. The pursuit of predicting large earthquakes has been a longstanding and challenging objective.
Short-term earthquake prediction relies on identifying a distinct and observable geophysical precursor signal, leading to the issuance of warnings ranging from minutes to months before a quake. Previous retrospective studies have suggested the potential existence of slow aseismic slip in faults preceding the main shock, which could serve as a precursor.
However, the link between these observations and seismic ruptures remains ambiguous. The uncertainty arises because these observations do not directly precede an event and often occur without an ensuing earthquake, casting doubt on the existence of a precise precursory signal for predicting large earthquakes.
In their research, Quentin Bletery and Jean-Mathieu Nocquet conducted an extensive global investigation to identify short-term precursory fault slip before significant earthquakes. They analyzed high-rate GPS time-series data from 3,026 geodetic stations worldwide and examined fault displacement up to two hours before 90 earthquakes with magnitudes of 7 and above.
Through a statistical analysis of this data, they revealed a subtle signal characterized by an exponential acceleration of fault slip near the earthquake's hypocenter, starting approximately two hours before the actual rupture.
The authors of the study propose that their findings indicate the presence of a precursory phase of slip in the initiation of many large earthquakes. Alternatively, the observations may represent the concluding part of a more extended and harder-to-measure process of precursory slip.
While the research presents evidence of a precursory signal preceding significant earthquakes, Bletery and Noquet advise caution, stating that current earthquake monitoring instruments do not have adequate coverage and precision to effectively detect or monitor precursory slip at the individual earthquake level.
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.- Roland Bürgmann