Global GPS measurements refer to p

Analysis of GPS time-series data from nearly 100 major earthquakes worldwide provided evidence of a precursor to fault slip that occurred two hours before the seismic rupture. Roland Bürgmann wrote in Related Perspective: “If it is confirmed that earthquake nucleation often involves a preliminary phase of hours, and the means can be developed to measure it reliably, a precursor warning can be issued.” The ability to predict large earthquakes has been a long-standing but elusive goal. Short-term earthquake prediction — the ability to issue a warning minutes to months in advance of an earthquake — depends on a specific and observable geophysical precursor signal. Previous retrospective studies of several large earthquakes have suggested that a preliminary phase of slow seismic slip may be observed in faults prior to a main shock. However, the relationship between these observations and seismic ruptures is poorly understood because they do not immediately precede an event and occur frequently without being followed by an earthquake. As a result, the existence of a clear precursor signal capable of predicting large earthquakes remains uncertain. Here, Quentin Bletery and Jean-Mathieu Nocquet present a global, systematic investigation of short-term preliminary fault slip before large earthquakes. Using global GPS time series data from 3,026 geodetic stations worldwide, Bletery and Noquet measured fault displacements up to 2 hours before 90 earthquakes of magnitude 7 and above occurred. Statistical analysis of the data revealed a subtle signal consistent with a period of exponential acceleration of fault slip near the final epicenter beginning approximately 2 hours before the rupture. According to the authors, the results indicate that many large earthquakes start with a pre-slip phase or that the observations represent the tail end of a longer, more difficult-to-measure pre-slip process. Although the study provides evidence for a precursor signal of large earthquakes, Bletery and Noquet note that currently deployed seismographs lack the coverage and accuracy required to identify or monitor commodity slip on the scale of individual earthquakes. “Although Bletery and Nocquet’s results suggest that there may indeed be an hour-long precursor phase, it is not clear whether such slow 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,” Borgman writes.

Article title

Preliminary phase of major earthquakes

The date the article was published

July 21, 2023

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