Examining the Connections Between Earthquake Swarms, Crustal Fluids, and Large Earthquakes in the Context of the 2020-2024 Noto Peninsula, Japan, Earthquake Sequence

Earthquake swarms are most commonly composed of small-magnitude earthquakes. However, a recent study by Yoshida, Uchida, et al. (2023, ) analyzed a swarm beneath the Noto Peninsula in Japan that, after more than two years of moderate-magnitude seismicity, triggered the moment magnitude (M-w) 6.2 Suzu mainshock in May 2023. Based on high-precision earthquake locations and a slip inversion of the mainshock, these authors found that the M-w 6.2 Suzu earthquake occurred on the updip extension of a fault that was active during the swarm, likely driven by increased fluid pressure. After publication of that paper, a much larger and more destructive M-w 7.5 event occurred nearby on 1 January 2024. These events underscore the potential for swarms to be precursors to large, damaging earthquakes. Forecasting the eventual evolution of swarms is currently very challenging but could be aided in the future by new observations and models.