Nonvolcanic , episodic tremor was first identified in southwest Japan in 2002 . Shortly after , the Geological Survey of Canada coined the term " episodic tremor and slip " to characterize observations of GPS measurements in the Vancouver Island area . Vancouver Island lies in 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
1700 Cascadia earthquake
1700 Cascadia earthquake
Episodic tremor and slip