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

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

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

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, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

(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 aseismi ...

Hayward Fault The Hayward Fault Zone is a right-lateral strike-slip geologic fault zone capable of generating destructive earthquakes. This fault is about long, situated mainly along the western base of the hills on the east side of San Francisco Bay. It runs ...

, and

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonics, tectonic boundary between the Pacific Plate and the North American Plate, and its motion is Fault (geology)#Strike-slip fau ...

Causes

Aseismic creep accommodates

far-field The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative ''near-field'' behaviors dominate close to the ante ...

motions on localized zones of deformation at

tectonic plate boundaries Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

. 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. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elonga ...

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 Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

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 mov ...

, 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 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 information about Earth ...

techniques are used to monitor

crustal deformation Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted t ...

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 i ...

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 the

in California and the

North Anatolian Fault The North Anatolian Fault (NAF) ( tr, Kuzey Anadolu Fay Hattı) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian Plate and the Anatolian Plate. The fault extends westward fro ...

in Turkey.{{cite journal , last1=Kaduri , first1=Maor , last2=Gratier , first2=Jean-Pierre , last3=Renard , first3=François , last4=Çakir , first4=Zidayin , last5=Lasserre , first5=Cécile , title=The implications of fault zone transformation on aseismic creep: Example of the North Anatolian Fault, Turkey , journal=Journal of Geophysical Research: Solid Earth , date=10 May 2017 , volume=122 , issue=6 , pages=4208-4236 , doi=10.1002/2016JB013803 , url=https://doi.org/10.1002/2016JB013803 , access-date=4 November 2022 Creep along the

Maacama Fault The Maacama Fault is a right lateral-moving (dextral) geologic fault located in the Coast Ranges of northwestern California. It is considered to be the northernmost segment of the Hayward Fault subsystem of the San Andreas Fault The San Andre ...

is about 8 mm per year, consistent with the steady movement along the rest of the

system.

References

External links

Tour of the Hayward Fault
- California State University at Hayward web site with images showing fault creep on the

.
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