A systematic global analysis GPS Time-series data from nearly 100 large earthquakes indicate that there is a precursory state for fault slip that occurs two hours before seismic rupture.
An analysis of Global Positioning System (GPS) time-series data from nearly 100 major earthquakes worldwide has revealed evidence for a precursory phase of fault slip occurring two hours before seismic rupture.
In a related perspective, Roland Bürgmann writes, “If it can be confirmed that earthquake nucleation often includes an hourly precursory phase, and methods are developed to measure it reliably, a precursory warning can be issued.”
The quest to predict large earthquakes is a long-standing but elusive goal.
The challenge of short-term earthquake prediction
Short-term earthquake prediction, which involves issuing warnings anywhere from minutes to months before an earthquake, depends on the presence of a clear and observable geophysical precursor signal. Previous retrospective studies have observed slow aseismic slip on faults ahead of the main shock, acting as a possible precursor. However, the relationship between these observations and seismic deformations remains unclear. This uncertainty arises from the fact that these observations do not directly represent an event and often occur without an earthquake, thus questioning the existence of an accurate prognostic signal for predicting large earthquakes.
A global search for pioneer fault slips
In this research, Quentin Bletery and Jean-Mathieu Nocquet present a comprehensive global search for short-term precursory fault slip before major earthquakes. Using global high-rate GPS time-series data from 3,026 geodetic stations worldwide, Pletary and Noquet evaluated the fault displacement two hours before 90 different earthquakes of magnitude 7 and above. Statistical analysis of this data revealed a subtle signal, aligned with the period of exponential acceleration of fault slip near the hypocenter of the earthquake, beginning two hours before rupture.
Significance and limitations of the study
According to the authors, these findings indicate that many large earthquakes begin on foreslip, or that observations may represent the end of a long and challenging period for measuring the process of foreslip. Bletery and Noquet warn that despite presenting evidence of a precursory signal that precedes large earthquakes, current earthquake monitoring tools lack the security and precision needed to detect or track precursory slip at the scale of individual earthquakes.
Bürgmann writes, “Although Bletery and Nocquet’s results suggest that there may indeed be an hourly precession phase, it is unclear whether such slow slip accelerations are clearly associated with large earthquakes or whether they can ever be measured for individual events. Accuracy Provide effective warning.
Reference: Quentin Bletery and Jean-Mathieu Nocquet, 20 July 2023, “Presentation of Great Earthquakes”, Science.