Abstract
The discovery of slow-slip phenomena has revolutionized our understanding
of how faults accommodate relative plate motions. Faults were previously
thought to relieve stress either through continuous aseismic sliding,
or as earthquakes resulting from instantaneous failure of locked
faults. In contrast, slow-slip events proceed so slowly that slip
is limited and only low-frequency (or no) seismic waves radiate.
We find that slow-slip phenomena are not unique to the depths (tens
of kilometres) of subduction zone plate interfaces. They occur on
faults in many settings, at numerous scales and owing to various
loading processes, including landslides and glaciers. Taken together,
the observations indicate that slowly slipping fault surfaces relax
most of the accrued stresses through aseismic slip. Aseismic motion
can trigger more rapid slip elsewhere on the fault that is sufficiently
fast to generate seismic waves. The resulting radiation has characteristics
ranging from those indicative of slow but seismic slip, to those
typical of earthquakes. The mode of seismic slip depends on the inherent
characteristics of the fault, such as the frictional properties.
Slow-slip events have previously been classified as a distinct mode
of fault slip compared with that seen in earthquakes. We conclude
that instead, slip modes span a continuum and are of common occurrence.
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