Temporarily Increased Recurrence Rate of Shallow Slow Slip Events Driven by Significant Afterslip Following the 2012 Mw 7.6 Nicoya Earthquake

Abstract

Slow slip events (SSEs) release tectonic strain without causing sudden ground shaking. SSEs have been observed at many subduction zones, some dynamically triggered by stress changes due to the passage of seismic waves. However, there are limited observations of SSEs induced by post-seismic deformation. Here, we report a significant increase in the recurrence rate of SSEs in the shallow portion of the Nicoya megathrust following the 2012 M_w 7.6 earthquake. These shallow SSEs occurred immediately updip of the large afterslip zone and their recurrence rate returned to pre-earthquake level 1.5 years after the earthquake. In contrast, deeper SSE recurrence rate remained unchanged. Coulomb Failure Stress modeling indicates the shallow SSE area experienced substantial stress perturbation during afterslip, while the deeper megathrust did not. We interpret this temporarily increased shallow SSE recurrence rate to be driven by static stress loading from large afterslip.