Discovery
"Episodic tremor and slip" was coined by the Geological Survey of Canada around 2003 to describe observations of GPS measurements in the Vancouver Island area. Vancouver Island is on the eastern, North American region of the Cascadia subduction zone. ETS events in Cascadia were observed to reoccur cyclically with a period of approximately 14 months. Analysis of measurements led to the successful prediction of ETS events in following years (e.g., 2003, 2004, 2005, and 2007). 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. Tremor is a weak seismological signal only detectable by very sensitive seismometers. Recent episodes of tremor and slip in the Cascadia region have occurred down-dip of the region ruptured in the 1700 Cascadia 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. Slow slip is not accompanied by tremor in the Hikurangi Subduction Zone.
Read more about this topic: Episodic Tremor And Slip
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