Stress Transfer From Slow Slip Events to Earthquake Swarms as a Cycle in the Southernmost Ryukyu Subduction Zone

Abstract Recent megathrust earthquakes preceded by slow slip events highlight static stress transfer as a key triggering mechanism. However, there are limited insights into the interplay between static stress transfer and elevated fluid pressure before earthquake triggering. In the southernmost Ryukyu subduction zone, we focus on changes in b ‐value, principal stress axes, and Coulomb failure stress during three earthquake swarms. They recurred with much larger events and were preceded by slow slip events. The b ‐value dropped from 1.0 to below 0.7 during the initial phases of slow slips. The lowest b ‐value was observed during the 2009 slow slip event, for which a 30° change in the σ 1 ‐axis orientation can be observed. The overlap between swarms and Coulomb stress transfer in front of slow slip patches further supports the amplification of swarm magnitudes. These findings underscore a clear stress transfer that precedes fluid overpressure in the enlargement of triggered earthquake size.