HOME

TheInfoList



OR:

In
seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
, a supershear earthquake is an
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, fr ...
in which the propagation of the rupture along the fault surface occurs at speeds in excess of the seismic
shear wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because th ...
(S-wave) velocity. This causes an effect analogous to a
sonic boom A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to ...
.


Rupture propagation velocity

During seismic events along a fault surface the displacement initiates at the focus and then propagates outwards. Typically for large earthquakes the focus lies towards one end of the slip surface and much of the propagation is unidirectional (e.g. the 2008 Sichuan and
2004 Indian Ocean earthquake An earthquake and a tsunami, known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake, occurred at 07:58:53 local time ( UTC+7) on 26 December 2004, with an epicentre off the west coast of northern ...
s). Theoretical studies have in the past suggested that the upper bound for propagation velocity is that of
Rayleigh waves Rayleigh waves are a type of surface acoustic wave that travel along the surface of solids. They can be produced in materials in many ways, such as by a localized impact or by piezo-electric transduction, and are frequently used in non-destructi ...
, approximately 0.92 of the shear wave velocity. However, evidence of propagation at velocities between S-wave and
compressional wave Longitudinal waves are waves in which the vibration of the medium is parallel ("along") to the direction the wave travels and displacement of the medium is in the same (or opposite) direction of the wave propagation. Mechanical longitudinal w ...
(P-wave) values have been reported for several earthquakesArchuleta,R.J. 1984
A faulting model for the 1979 Imperial Valley earthquake
J. Geophys. Res., 89, 4559–4585.
in agreement with theoretical and laboratory studies that support the possibility of rupture propagation in this velocity range.


Occurrence

Evidence of rupture propagation at velocities greater than S-wave velocities expected for the surrounding crust have been observed for several large earthquakes associated with
strike-slip faults In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
. During strike-slip, the main component of rupture propagation will be horizontal, in the direction of displacement, as a Mode II (in-plane) shear crack. This contrasts with a dip-slip rupture where the main direction of rupture propagation will be perpendicular to the displacement, like a Mode III (anti-plane) shear crack. Theoretical studies have shown that Mode III cracks are limited to the shear wave velocity but that Mode II cracks can propagate between the S and P-wave velocities and this may explain why supershear earthquakes have not been observed on dip-slip faults.


Initiation of supershear rupture

The rupture velocity range between those of Rayleigh waves and shear waves remains forbidden for a Mode II crack (a good approximation to a strike-slip rupture). This means that a rupture cannot accelerate from Rayleigh speed to shear wave speed. In the "Burridge–Andrews" mechanism, supershear rupture is initiated on a 'daughter' rupture in the zone of high shear stress developed at the propagating tip of the initial rupture. Because of this high stress zone, this daughter rupture is able start propagating at supershear speed before combining with the existing rupture. Experimental shear crack rupture, using plates of a photoelastic material, has produced a transition from sub-Rayleigh to supershear rupture by a mechanism that "qualitatively conforms to the well-known Burridge-Andrews mechanism".


Geological effects

The high rates of strain expected near faults that are affected by supershear propagation are thought to generate what is described as pulverized rocks. The pulverization involves the development of many small microcracks at a scale smaller than the grain size of the rock, while preserving the earlier
fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not ...
, quite distinct from the normal brecciation and
cataclasis A cataclastic rock is a type of fault rock that has been wholly or partly formed by the progressive fracturing and comminution of existing rocks, a process known as ''cataclasis''. Cataclasis involves the granulation, crushing, or milling of the ori ...
found in most fault zones. Such rocks have been reported up to 400 m away from large strike-slip faults, such as the San Andreas Fault. The link between supershear and the occurrence of pulverized rocks is supported by laboratory experiments that show very high strain rates are necessary to cause such intense fracturing.


Examples


Directly observed

* 1999 Izmit earthquake, magnitude ''M''w 7.6 associated with strike-slip movement on the
North Anatolian Fault Zone 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 f ...

Bouchon, M., M.-P. Bouin, H. Karabulut, M. N. Toksöz, M. Dietrich, and Ares J. Rosakis, A. J. Rosakis (2001)
How Fast is Rupture During an Earthquake ? New Insights from the 1999 Turkey Earthquakes
Geophys. Res. Lett., 28(14), 2723–2726.]
*
1999 Düzce earthquake The 1999 Düzce earthquake occurred on 12 November at with a moment magnitude of 7.2 and a maximum Mercalli intensity of IX (''Violent''), causing damage and at least 845 fatalities in Düzce, Turkey. The epicenter was approximately to the east ...
, magnitude ''M''w 7.2 associated with strike-slip movement on the North Anatolian Fault Zone *
2001 Kunlun earthquake The 2001 Kunlun earthquake also known as the 2001 Kokoxili earthquake, occurred on 14 November 2001 at 09:26 UTC (17:26 local time), with an epicenter near Kokoxili, close to the border between Qinghai and Xinjiang in a remote mountainous regio ...
, magnitude ''M''w 7.8 associated with strike-slip movement on the Kunlun fault *
2002 Denali earthquake The 2002 Denali earthquake occurred at 22:12:41 UTC (1:12 PM Local Time) November 3 with an epicenter 66 km ESE of Denali National Park, Alaska, United States. This 7.9 Mw earthquake was the largest recorded in the United States in 37 year ...
, magnitude ''M''w 7.9 associated with strike-slip movement on the Denali Fault *
2010 Yushu earthquake The 2010 Yushu earthquake struck on April 14 and registered a magnitude of 6.9 Mw ( USGS, EMSC) or 7.1 MsYushu Fault *
2012 Indian Ocean earthquakes The 2012 Indian Ocean earthquakes were magnitude 8.6 and 8.2 undersea earthquakes that struck near the Indonesian province of Aceh on 11 April at 15:38 local time. Initially, authorities feared that the initial earthquake would cause a tsunam ...
, magnitude ''M''w 8.6 associated with strike-slip on several fault segments - the first supershear event recognised in oceanic lithosphere. *
2013 Craig, Alaska earthquake The 2013 Craig, Alaska earthquake (also known as the Queen Charlotte Fault earthquake) struck on January 5, at 12:58 am ( UTC–7) near the city of Craig and Hydaburg, on Prince of Wales Island. The 7.5 earthquake came nearly three months afte ...
, magnitude ''M''w 7.6 associated with strike-slip on the Queen Charlotte Fault - the first supershear event recognised on an oceanic plate boundary. *
2014 Aegean Sea earthquake An earthquake occurred in the northern Aegean Sea between Greece and Turkey on May 24, 2014. It had a moment magnitude of 6.9 and a maximum Mercalli intensity of VIII (''Severe''). Serious damage was reported on the Turkish island of Imbros and t ...
, magnitude ''M''w 6.9, supershear was recognised during the second sub-event. * 2015 Tajikistan earthquake, magnitude ''M''w 7.2, supershear slip on two segments, with normal slip at the restraining bend linking them. * 2016 Romanche fracture zone earthquake, magnitude 7.1, westwards-directed supershear rupture following an initial easterly-travelling phase on the Romanche ocean transform fault in the equatorial Atlantic * 2017 Komandorsky Islands earthquake, magnitude ''M''w 7.7, supershear transition followed a rupture jump across a fault
stepover The step over (also known as the ''pedalada'', the ''denílson'', or the ''scissors'', or the ''roeder shuffle'') is a dribbling move, or feint, in association football, used to fool a defensive player into thinking the offensive player, in posse ...
. * 2018 Swan Islands earthquake, 7.5 earthquake consisted of three sub-events with a compact rupture area and large cosesimic slip. * 2018 Sulawesi earthquake, magnitude ''M''w 7.5, associated with strike-slip movement on the
Palu-Koro Fault The Palu-Koro Fault or Palu-Koro Fault System is a major active NNW-SSE trending left-lateral strike-slip fault zone on the island of Sulawesi in Indonesia. It caused the 2018 Sulawesi earthquake and tsunami. Geometry It extends from near Dondow ...
* 2020 Caribbean Sea earthquake, magnitude ''M''w 7.7, unilateral rupture propagation westward from the epicenter along a 300 km section of the Oriente transform fault with two episodes of supershear rupture *
2021 Maduo earthquake The 2021 Maduo earthquake, also known as the 5.22 earthquake struck Madoi County in Qinghai Province, China on 22 May at 02:04 local time. The earthquake had a moment magnitude and surface-wave magnitude of 7.4. Highway bridges, roads and walls ...
, 7.4 earthquake in the Tibetan Plateau. This earthquake ruptured bilaterally for a length of 170 km within the Bayan Har block.


Inferred

*
1906 San Francisco earthquake At 05:12 Pacific Standard Time on Wednesday, April 18, 1906, the coast of Northern California was struck by a major earthquake with an estimated moment magnitude of 7.9 and a maximum Mercalli intensity of XI (''Extreme''). High-intensity ...
, magnitude 7.8 associated with strike-slip movement on the
San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal) ...
*
1979 Imperial Valley earthquake The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time (23:16 UTC) on 15 October just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja Calif ...
, magnitude 6.4 associated with slip on the
Imperial Fault The Imperial Fault Zone is a system of geological faults located in Imperial County in the Southern California region, and adjacent Baja California state in Mexico. It cuts across the border between the United States and Mexico. Geology The I ...
* 1990 Sakhalin earthquake, 7.2 earthquake at over 600 km depth inferred to have ruptured at supershear speeds. *
2013 Okhotsk Sea earthquake The 2013 Okhotsk Sea earthquake occurred with a moment magnitude of 8.3 at 15:44:49 local time (05:44:49 UTC) on 24 May. It had an epicenter in the Sea of Okhotsk and affected primarily (but not only) Asian Russia, especially the Kamchatka Penins ...
magnitude 6.7 aftershock was an extremely deep (640 kilometers (400 miles)) supershear as well as unusually fast at "eight kilometers per second (five miles per second), nearly 50 percent faster than the shear wave velocity at that depth."


See also

*
Slow earthquake A slow earthquake is a discontinuous, earthquake-like event that releases energy over a period of hours to months, rather than the seconds to minutes characteristic of a typical earthquake. First detected using long term strain measurements, most ...


References


Further reading

* * {{citation, title=Seismic boom: Breaking the quake barrier, url=https://www.newscientist.com/article/mg20327191-400-seismic-boom-breaking-the-quake-barrier/, date=29 July 2009, author=Richard Fisher, work=New Scientist


External links


Eric Dunham's webpage on Supershear Dynamics
Seismology Types of earthquake Strike-slip earthquakes