1. Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, British Columbia V8L 1B9, Canada

Correspondence to: Honn Kao¹ Correspondence and requests for materials should be addressed to H.K. (Email: hkao@nrcan.gc.ca).

Abstract

The Cascadia subduction zone is thought to be capable of generating major earthquakes with moment magnitude as large as M_w = 9 at an interval of several hundred years^{1, 2, 3}. The seismogenic portion of the plate interface is mostly offshore and is currently locked, as inferred from geodetic data^{4, 5, 6}. However, episodic surface displacements—in the direction opposite to the long-term deformation motions caused by relative plate convergence across a locked interface—are observed about every 14 months with an unusual tremor-like seismic signature^{7, 8, 9}. Here we show that these tremors are distributed over a depth range exceeding 40 km within a limited horizontal band. Many occurred within or close to the strong seismic reflectors above the plate interface where local earthquakes are absent, suggesting that the seismogenic process for tremors is fluid-related. The observed depth range implies that tremors could be associated with the variation of stress field induced by a transient slip along the deeper portion of the Cascadia interface or, alternatively, that episodic slip is more diffuse than originally suggested.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.