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

¹ Institute of Geology
China Earthquake Administration
P.O. Box 9803
Beijing 100029, China

Department of Earth and Space Sciences
UCLA
3806 Geology
595 Charles Young Drive
Los Angeles, California 90095-1567
 (Z.-K.S.)

² Second Monitoring Center
China Earthquake Administration
Xiying Road
Xi’an, China
 (Q.W.)

³ Department of Earth and Planetary Science
University of California
Berkeley, California 94720-4767
 (R.B.)

⁴ College of Disaster Prevention Technology
China Earthquake Administration
Yanjiao, Hebei 101601
China
 (Y.W.)

⁵ Department of Geophysics
Peking University
Beijing 1000871
China
 (J.N.)

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 Chandler 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.