seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

, a supershear earthquake is when 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 t ...

(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 On 26 December 2004, at 07:58:53 local time (UTC+07:00, UTC+7), a major earthquake with a magnitude of 9.2–9.3 struck with an epicenter, epicentre off the west coast of Aceh in northern Sumatra, Indonesia. The Submarine earthquake, undersea ...

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-destruc ...

, approximately 0.92 of the shear wave velocity. However, evidence of propagation at velocities between S wave and

compressional wave Longitudinal waves are waves which oscillate in the direction which is parallel to the direction in which 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. Systematic studies indicate that supershear rupture is common in large strike-slip earthquakes.

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 Shear stress (often denoted by , Greek alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross secti ...

developed at the propagating tip of the initial rupture. Because of this high stress zone, this daughter rupture is able to 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, and different types of fabric. At first, the word "textiles" only referred to woven fabrics. However, weaving is no ...

, quite distinct from the normal brecciation and cataclasis 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; ) 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 ...

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, magnitude ''M''_w 7.2 associated with strike-slip movement on the North Anatolian Fault Zone *

2001 Kunlun earthquake 1 (one, unit, unity) is a number, numeral, and glyph. It is the first and smallest positive integer of the infinite sequence of natural numbers. This fundamental property has led to its unique uses in other fields, ranging from science to sp ...

, 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 Alaska Time Zone, Local Time) November 3 with an epicenter 66 km ESE of Denali National Park, Alaska, United States. This 7.9 Moment magnitude scale, Mw earthquake was the larges ...

, magnitude ''M''_w 7.9 associated with strike-slip movement on the

Denali Fault The Denali Fault is a major intracontinental dextral (right lateral) Fault (geology)#Strike-slip faults, strike-slip fault in western North America, extending from northwestern British Columbia, Canada to the central region of the U.S. state of ...

2008 Sichuan earthquake An earthquake occurred in the province of Sichuan, China at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 (7.9–8.3 ), the earthquake's epicenter was located boxing the compass, west-northwest of Chengdu, the provincial ...

, magnitude ''M''_w 7.9, supershear was recognised during a sub-event on a strike-slip fault near the Longmenshan 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 Moment magnitude scale, magnitude 8.6 and 8.2 Submarine earthquake, undersea earthquakes that struck near the Indonesian province of Aceh on 11 April at 15:38 local time. Initially, authorities feared that ...

, magnitude ''M''_w 8.6 associated with strike-slip on several fault segments – the first supershear event recognised in oceanic

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

. *

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. * 2013 Balochistan earthquake ''M''_w 7.7 associated with strike-slip movement on a curved fault with supershear rupture speed. * 2014 Aegean Sea earthquake, 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. * 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 Dondo ...

* 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, 7.4 earthquake in the Tibetan Plateau. This earthquake ruptured bilaterally for a length of 170 km within the Bayan Har block. *

2023 Turkey–Syria earthquakes On 6 February 2023, at 04:17 Time in Turkey, TRT (01:17 Coordinated Universal Time, UTC), a 7.8 earthquake struck southern and central Turkey and northern and western Ba'athist Syria, Syria. The epicenter was west–northwest ...

, 7.8 and 7.6 earthquakes in Turkey. Supershear rupture initiated along both mainshocks, with the latter attaining a maximum velocity of per second. *

2025 Myanmar earthquake On 28 March 2025 at 12:50:52 Myanmar Time, MMT (06:20:52 UTC), a 7.7–7.9 earthquake struck the Sagaing Region of Myanmar, with an epicenter close to Mandalay, the country's second-largest city. The strike-slip shock achieved a maximum Modif ...

, 7.7 earthquake ruptured at supershear velocity along more than of the

Sagaing Fault The Sagaing Fault is a major fault in Myanmar, a mainly continental right-lateral transform fault between the Indian plate and Sunda plate. It links the divergent boundary in the Andaman Sea with the zone of active continental collision along t ...

Inferred

1906 San Francisco earthquake At 05:12 AM Pacific Time Zone, Pacific Standard Time on Wednesday, April 18, 1906, the coast of Northern California was struck by a major earthquake with an estimated Moment magnitude scale, moment magnitude of 7.9 and a maximum Mercalli inte ...

, magnitude 7.8 associated with strike-slip movement on the

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 ...

* 1979 Imperial Valley earthquake, magnitude 6.4 associated with slip on the Imperial Fault * 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 Pen ...

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."

References

External links

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