GPS data can detect large earthquakes hours before they happen

By Walter Beckwith, American Association for the Advancement of Science (AAAS) July 22, 2023

A comprehensive analysis of GPS time-series data indicates that a preliminary phase of fault slip occurred 2 hours before large earthquakes. However, the current inability of monitoring tools to detect such slips at the scale of individual earthquakes remains a major challenge for practical earthquake prediction.

A systematic global analysis of GPS time-series data for nearly 100 major earthquakes indicates that there is a preparatory phase for fault slip that occurs about 2 hours prior to seismic rupture.

Analysis of GPS time-series data from nearly 100 major earthquakes worldwide revealed evidence of a preparatory phase for fault slip, which occurs approximately two hours prior to seismic rupture.

In a related perspective, Roland Bürgmann writes, “If it can be confirmed that earthquake intensification often includes a preliminary phase of hours, and the means can be developed to measure it reliably, a precursor warning can be issued.”

The quest to predict large earthquakes is a long-term but elusive goal.

The challenge of short-term earthquake prediction

Short-term earthquake forecasting, which involves issuing a warning anywhere from minutes to months in advance of an earthquake, depends on the presence of a clear and observable geophysical predecessor signal. Previous retrospective studies have suggested that slow seismic slip can be seen in faults before the main shock, and serves as a possible precursor. However, the relationship 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 earthquake, leaving an accurate preliminary signal for the prediction of the large earthquakes involved.

Global search for vanguard error slip

In this paper, Quentin Bletery and Jean-Mathieu Nocquet present a comprehensive global investigation of short-term pre-fault slip before large earthquakes. Using global GPS time series data from 3,026 geodetic stations worldwide, Bletery and Noquet assessed fault displacements up to 2 hours prior to 90 different earthquakes of magnitude 7 and above. Statistical analysis of this data revealed a subtle signal, consistent with a period of exponential acceleration of fault slip near the epicenter, beginning approximately 2 hours before the rupture.

The importance of the study and its limitations

According to the authors, these results indicate that many large earthquakes begin with a pre-slip phase, or the observations may represent a concluding part of a longer and more difficult pre-slip measurement process. Despite providing evidence of a precursor signal that preceded large earthquakes, Bletery and Noquet caution that current seismic monitoring tools lack the coverage and resolution needed to detect or monitor passive slip on the scale of individual earthquakes.

Borgmann writes, “Although Bletery and Nocquet’s results suggest that there may indeed be an hour-long preliminary phase in place, it is not clear whether such slow-slip accelerations are clearly associated with large earthquakes or whether they can be measured for individual events with the precision necessary to provide a useful warning.”

Reference: “The Prelude to Large Earthquakes” by Quentin Plettieri and Jean-Mathieu Noquet, Jul 20, 2023, Science.DOI: 10.1126/science.adg2565

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