New Study Suggests Precursory Phase of Fault Slip Occurs Two Hours Before Large Earthquakes
By Walter Beckwith, American Association for the Advancement of Science (AAAS)
July 22, 2023
A recent comprehensive analysis of GPS time-series data has provided new evidence for the existence of a precursory phase of fault slip that occurs approximately two hours before large earthquakes. However, the current limitations of monitoring tools to detect such slips on an individual earthquake scale pose a significant challenge for practical earthquake prediction.
The study, conducted by Quentin Bletery and Jean-Mathieu Nocquet, involved a systematic global analysis of GPS time-series data from nearly 100 large earthquakes. Using data from 3,026 geodetic stations worldwide, the researchers assessed fault displacement up to two hours before 90 earthquakes with a magnitude of 7 and above.
The statistical analysis of this data revealed a subtle signal indicating a period of exponential acceleration of fault slip near the earthquake’s hypocenter, beginning approximately two hours before the rupture. These findings suggest that many large earthquakes may initiate with a precursory phase of slip, or that the observations may represent the concluding part of a longer and more challenging to measure process of precursory slip.
Roland Bürgmann, in a related Perspective, emphasized the potential impact of these findings, stating, “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.”
However, despite the significance of these findings, Bletery and Nocquet caution that the current earthquake monitoring instruments lack the necessary coverage and precision to detect or monitor precursory slip at the scale of individual earthquakes. This limitation highlights the challenges that persist in practical earthquake prediction.
Bürgmann shares these concerns, noting, “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.”
The quest for short-term earthquake prediction, which involves issuing warnings from minutes to months before a quake, depends on identifying clear and observable geophysical precursor signals. While previous studies have proposed the presence of slow aseismic slip as a possible precursor, the connection between these observations and seismic ruptures remains uncertain. The lack of a precise precursory signal leaves the ability to predict large earthquakes in question.
The study by Bletery and Nocquet addresses this challenge by providing evidence of a precursory signal preceding large earthquakes. However, further research and the development of more advanced monitoring tools are necessary to fully understand and utilize this potential precursor warning.
Reference: “The precursory phase of large earthquakes” by Quentin Bletery and Jean-Mathieu Nocquet, 20 July 2023, Science.
DOI: 10.1126/science.adg2565