Comprehensive analysis of GPS time series data suggests that a precursor phase of fault slip occurs two hours before major earthquakes. However, the current inability of monitoring tools to detect such slips at the scale of individual earthquakes remains a significant challenge for practical earthquake prediction.

A systematic global analysis of GPS time series data from nearly 100 large earthquakes suggest the existence of a precursor fault-slip phase that occurs approximately two hours before seismic rupture.

Analysis of Global Positioning System (GPS) time-series data from nearly 100 large earthquakes around the world uncovered evidence of a precursor phase of fault slip, which occurs about two hours before seismic rupture.

From a related perspective, Roland Bürgmann writes: “If it can be confirmed that the nucleation of an earthquake often involves a precursor phase of several hours, and the means can be developed to measure it reliably, an early warning could be issued.

The quest to predict great earthquakes is a long-standing but elusive goal.

The Challenge of Short-Term Earthquake Prediction

Short-term earthquake prediction, which involves issuing a warning minutes to months before an earthquake, depends on the presence of a clear and observable geophysical warning signal. Previous retrospective studies have proposed that slow aseismic slip can be observed in faults upstream of the main shock, serving as a possible precursor. However, the link between these observations and seismic ruptures remains unclear. This uncertainty arises because these observations do not directly precede an event and often occur without an ensuing earthquake, leaving the existence of an accurate precursor signal to predict the large earthquakes in question.

A global preliminary fault record search

In this research, Quentin Bletery and Jean-Mathieu Nocquet present a comprehensive global search for short-term precursor fault slip before large earthquakes. Using global high-throughput GPS time series data from 3,026 geodetic stations around the world, Bletery and Noquet assessed fault displacement up to two hours before 90 different magnitude 7+ earthquakes. Statistical analysis of these data revealed a subtle signal, aligned with a period of exponential acceleration of fault slip near the hypocenter of the earthquake, beginning about two hours before rupture.

Significance and limitations of the study

According to the authors, these results suggest that many large earthquakes begin with a precursor slip phase, or the observations may represent the final part of a longer and more difficult to measure precursor slip process. Although they present evidence of a precursor signal preceding large earthquakes, Bletery and Noquet caution that current earthquake monitoring instruments lack the coverage and precision needed to detect or monitor precursor landslides at the scale of individual earthquakes.

Bürgmann writes: “Although the results of Bletery and Nocquet suggest that there may indeed be a precursor phase of several hours, it is not clear whether such slow-slip accelerations are clearly associated with large earthquakes or whether they could ever be measured for individual events with the accuracy necessary to provide a useful warning.

Reference: “The precursor phase of large earthquakes” by Quentin Bletery and Jean-Mathieu Nocquet, July 20, 2023, Science.
DOI: 10.1126/science.adg2565