geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

s. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip include faults in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

(e.g.

Calaveras Fault The Calaveras Fault is a major branch of the San Andreas Fault System that is located in northern California in the San Francisco Bay Area. Activity on the different segments of the fault includes moderate and large earthquakes as well as aseis ...

, Hayward Fault, and

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

Causes

Aseismic creep accommodates far-field motions on localized zones of deformation at

tectonic plate boundaries Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

. The underlying causes of aseismic creep are primarily attributed to poor frictional strength of the fault, low

normal stress In continuum mechanics, stress is a physical quantity that describes forces present during deformation. For example, an object being pulled apart, such as a stretched elastic band, is subject to ''tensile'' stress and may undergo elongati ...

acting on the fault in the shallow crust, and excessive pore-fluid pressures, which limit the viable amount of

on a fault. The frictional reaction of geologic materials can explain the transition from seismic to aseismic deformation with depth. Friction along faults can cause sudden slips with associated stress drops (

s), along with phases of no motion as stress recharges.

Measurements

Knowing how creep rates vary temporally and spatially along faults has important implications for predicting the timing, locations, and potential sizes of future

s as well as the mechanics of fault behavior. Measurements of inter-seismic strain, as well as the associated pattern of

coupling A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end mo ...

, are also crucial because they reveal the pockets where stress is building up and may be released in future seismic ruptures. The emergence of space-based geodesy and newly developed

remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...

techniques are used to monitor crustal deformation in order to track aseismic creep on a fault.

Theodolite A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and ...

surveys are used with alignment arrays to track the creep. These data may then be used to restrict a fault's seismic capacity.

Examples

Aseismic creep exists along the

in Hollister,

. Streets crossing the fault in Hollister show significant offset. Several houses sitting atop the fault are notably twisted, yet still habitable. The city attracts geologists and geology students almost weekly. Other examples of faults that have experienced aseismic creep include a

in California and the

North Anatolian Fault The North Anatolian Fault (NAF; ) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian plate and the Anatolian sub-plate. The fault extends westward from a junction with the Ea ...

in Turkey. Creep along the Maacama Fault is about {{Convert, 8, mm, abbr=on per year, consistent with the steady movement along the rest of the Hayward Fault system.

References

External links

Tour of the Hayward Fault
– California State University at Hayward web site with images showing fault creep on the Hayward Fault.
Fremont Earthquake Exhibit – The Hayward Fault Exposed
msnucleus.org, K-12 math and science education site. Structural geology Seismology

Causes

Measurements

Examples

See also

References

External links