Source: Geophysical Research Letters
Given the damage that large earthquakes cause, humans have naturally spent a great deal of effort looking for signs of precursors in the years to months before they occur. Evidence for such preparatory behavior would help society respond better to earthquakes as well as help scientists understand the fundamental underlying physics. Unfortunately, for the most part, evidence for precursory activity has remained speculative or poorly documented.
Tanaka  wrote a provocative paper providing tantalizing evidence suggesting that one of the largest earthquakes to occur this century, the 2004 M9.0 Sumatra-Andaman earthquake, had a statistically significant change in the tidal triggering of small nearby earthquakes in the decade preceding the 2004 earthquake.
Beaucé et al.  present a follow-up study to test the hypothesis of whether the well-documented 2019 M7.1 Ridgecrest earthquake has enhanced tidal sensitivity in the years prior to the mainshock. Interestingly, using a new earthquake catalog with over 150,000 events, they find a robust change in nearby tidal triggering in the years before the Ridgecrest earthquake. This clear result strengthens the Tanaka’s hypothesis and suggests that perhaps all well-observed earthquakes have precursory signs that could be utilized to help with earthquake forecasting.
Citation: Beaucé, E., Poli, P., Waldhauser, F., Holtzman, B., & Scholz, C. (2023). Enhanced tidal sensitivity of seismicity before the 2019 magnitude 7.1 Ridgecrest, California earthquake. Geophysical Research Letters, 50, e2023GL104375. https://doi.org/10.1029/2023GL104375
—Victor Tsai, Associate Editor, Geophysical Research Letters