Episodic tremor and slip

[2] Shortly afterwards, the Geological Survey of Canada coined the term "episodic tremor and slip" to characterize observations of GPS measurements in the Vancouver Island area.

In Cascadia, these events are marked by about two weeks of 1 to 10 Hz seismic trembling and non-earthquake ("aseismic") slip on the plate boundary equivalent to a magnitude 7 earthquake.

Since the initial discovery of this seismic mode in the Cascadia region, slow slip and tremor have been detected in other subduction zones around the world, including Japan and Mexico.

A GPS marker on the surface of the North American plate above the locked region will trend eastward as it is dragged by the subduction process.

[5] Unique characteristics of slow slip events include periodicity on timescales of months to years, focus near or down-dip of the locked zone, and along-strike propagation of 5 to 15 km/d.

Because slow slip events occur in subduction zones, their relationship to megathrust earthquakes is of economic, human, and scientific importance.

If the slow slip event extends into the seismogenic zone, accumulated stress would be released, decreasing the risk of a catastrophic earthquake.

[14] Furthermore, while earthquakes are caused by the rupture of faults, tremor is generally attributed to underground movement of fluids (magmatic or hydrothermal).

[22] Mathematical modelling has successfully reproduced the periodicity of episodic tremor and slip in the Cascadia region by incorporating this dehydration effect.

[23] In this interpretation, tremor may be enhanced where the subducting oceanic crust is young, hot, and wet as opposed to older and colder.

[4] Recent contributions in mathematical modelling reproduce the sequences of Cascadia and Hikurangi (New Zealand), and suggest in-situ dehydration as the cause for the episodic tremor and slip events.