Slide 1
Fault motion can be sudden or slow
A fault is a zone where rock blocks move relative to one another. Motion may occur suddenly in earthquakes or slowly as creep.
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A single fault can contain both creeping and locked sections. Observing gentle movement at the surface therefore does not establish that the entire fault is releasing all its accumulated strain without earthquakes.
Slide 2
Locked patches let surrounding rock store elastic energy
Where friction prevents sliding, continued tectonic motion deforms surrounding rock. Stored elastic energy can be released when a patch slips rapidly.
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The blocks need not remain undeformed while they wait. Small distributed changes in shape can be measured across a region, giving geodesists information about how motion is being accommodated between earthquakes.
Slide 3
Friction changes with minerals, fluids and temperature
Fault behaviour depends on mineral composition, temperature, fluids and how friction responds to sliding. No single visible crack reveals all these properties.
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Laboratory experiments test rock samples under controlled pressure and sliding conditions. Their results help interpret fault behaviour, but scaling from a specimen to a heterogeneous natural fault remains an important challenge.
Slide 4
Creep can shift stress to neighbouring sections
Slow slip can reduce strain in one area while changing the stress applied to neighbouring sections. It is part of a connected mechanical system.
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A locked patch may be loaded by motion around it. This is why a map of creeping and locked regions matters more than a simple label that describes an entire fault as either safe or dangerous.
Slide 5
Repeated measurements reveal the connected motion
Scientists use surface surveys, satellite measurements and instruments across faults to track deformation. Combining records reveals patterns missed by one short observation.
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These measurements improve understanding of earthquake potential without providing a precise date for the next rupture. Fault conditions evolve, and a measured creep rate is not a countdown clock for a particular event.
Sources
- Earthquake Processes and Effects
US Geological Survey
- Rock Physics: Creeping Faults
US Geological Survey