Pole-Tide Modulation of Slow Slip Events at Circum-Pacific Subduction Zones

Abstract

Episodic slow slip (ESS) events have been detected at several circum- Pacific subduction zones, such as Cascadia, Japan, and Mexico. Notably, at least eight ESS events along the northern Cascadia subduction zone recurred with a period of 13-16 months. We study the relationship between pole-tide (associated with Chan- dler wobble with a period of 14 months)-induced stress and the occurrence of the ESS events. Our quantitative analysis shows that 14 of the 20 documented ESS events occurred during the ascension phase, prior to the maximum, of a pole-tide-induced Coulomb failure stress change, and three events occurred at the stress-change peak. The pole tides modulate the stress field at the downdip edge of the transition zone along the plate interface and may trigger ESS events when conditions are favorable. The phase advance of the triggered events with respect to the induced Coulomb failure stress change may reflect that the fault slip is dictated by a rate- and state- dependent friction law inferred from laboratory experiments.