Episodic tremor and slip ETS represents a newly discovered mode of fault behavior occurring just below the locked zone that generates great earthquakes. Initially discovered in subduction zones, this new slip mechanism can release energy equivalent to at least a magnitude 7 earthquake! While this is a tremendous energy release, no one ever feels these events because they occur as slow slip episodes lasting weeks or months. As the plates move, high-precision Global Positioning System GPS monuments record the magnitude and direction of motion while seismometers record the low amplitude seismic waves released. Jump to. Sections of this page.
Annual Seismic 'Slow-Slip' Is On, But Not In Puget Sound — Yet
Tide gauges capture tremor episodes in cascadian subduction zone -- ScienceDaily
Earth, Planets and Space. Slip events with an average duration of about 10 days and effective total slip displacements of severalc entimetres have been detected on the deeper 25 to 45 km part of the northern Cascadia subduction zone interface by observing transient surface deformation on a network of continuously recording Global Positioning System GPS sites. The slip events occur down-dip from the currently locked, seismogenic portion of the subduction zone, and, for the geographic region around Victoria, British Columbia, repeat at 13 to 16 month intervals. These episodes of slip are accompanied by distinct, low-frequency tremors, similar to those reported in the forearc region of southern Japan.
Tide gauges capture tremor episodes in cascadian subduction zone
ETS is what seismologists call a process that has been observed in some fault zones. First noted in Japan in , it involves repeated episodes of slow sliding, one plate against the other, accompanied by energetic seismic noise called tremor. Over the period of a few weeks, the slip and tremor area grows, eventually extending over an area of several hundred square miles, and releasing the energy equivalent to a magnitude 6. ETS was first observed in subduction zones, where one slab or plate is pulled by gravity beneath another plate. The pull is constant and the subducting plate moves continuously like a conveyor belt, regardless of what happens above or below it.
Slow Slip episodes affecting southern British Columbia and northern Washington have been occurring every 14 months or so since at least the s. The PNSN monitors the non-volcanic tremor associated with slow slip and has deployed additional seismometers from time to time to record expected tremor events to gain insight into the process and into the stresses that eventually will lead to the region's next major earthquake. Many different techniques are used to study this phenomenon.