Episodic tremor and slip

Last updated

Episodic tremor and slip (ETS) is a seismological phenomenon observed in some subduction zones that is characterized by non-earthquake seismic rumbling, or tremor, and slow slip along the plate interface. Slow slip events are distinguished from earthquakes by their propagation speed and focus. In slow slip events, there is an apparent reversal of crustal motion, although the fault motion remains consistent with the direction of subduction. ETS events themselves are imperceptible to human beings and do not cause damage. [1]

Contents

Discovery

Structure of the Cascadia subduction zone. The Juan de Fuca Plate is subducting northeastward under the North American Plate. Cascadia earthquake sources.png
Structure of the Cascadia subduction zone. The Juan de Fuca Plate is subducting northeastward under the North American Plate.

Nonvolcanic, episodic tremor was first identified in southwest Japan in 2002. [2] Shortly afterwards, the Geological Survey of Canada coined the term "episodic tremor and slip" to characterize observations of GPS measurements in the Vancouver Island area. [3] Vancouver Island lies in the eastern, North American region of the Cascadia subduction zone. ETS events in Cascadia were observed to reoccur cyclically with a period of approximately 14 months. [4] Analysis of measurements led to the successful prediction of ETS events in following years (e.g., 2003, 2004, 2005, and 2007). In Cascadia, these events are marked by about two weeks of 1 to 10 Hz seismic trembling and non-earthquake ("aseismic") slip on the plate boundary equivalent to a magnitude 7 earthquake. (Tremor is a weak seismological signal only detectable by very sensitive seismometers.) Recent episodes of tremor and slip in the Cascadia region have occurred down-dip of the region ruptured in the 1700 Cascadia earthquake.

Since the initial discovery of this seismic mode in the Cascadia region, slow slip and tremor have been detected in other subduction zones around the world, including Japan and Mexico. [5] Slow slip is not accompanied by tremor in the Hikurangi Subduction Zone. [6]

Every five years a year-long quake of this type occurs beneath the New Zealand capital, Wellington. It was first measured in 2003, and has reappeared in 2008 and 2013. [7]

Characteristics

Slip behaviour

GPS measurements from Victoria, British Columbia show periodic reversals in crustal deformation in the North American region of the Cascadia Subduction Zone. Displacement of Albert Head GPS Station, Victoria, British Columbia, 2005-2012.svg
GPS measurements from Victoria, British Columbia show periodic reversals in crustal deformation in the North American region of the Cascadia Subduction Zone.

In the Cascadia subduction zone, the Juan de Fuca Plate, a relic of the ancient Farallon Plate, is actively subducting eastward underneath the North American Plate. The boundary between the Juan de Fuca and North American plates is generally "locked" due to interplate friction. A GPS marker on the surface of the North American plate above the locked region will trend eastward as it is dragged by the subduction process. Geodetic measurements show periodic reversals in the motion (i.e., westward movement) of the overthrusting North American Plate. [4] During these reversals, the GPS marker will be displaced to the west over a period of days to weeks. Because these events occur over a much longer duration than earthquakes, they are termed "slow slip events".

Slow slip events have been observed to occur in the Cascadia, Japan, and Mexico subduction zones. [5] Unique characteristics of slow slip events include periodicity on timescales of months to years, focus near or down-dip of the locked zone, and along-strike propagation of 5 to 15 km/d. [5] In contrast, a typical earthquake rupture velocity is 70 to 90% of the S-wave velocity, or approximately 3.5 km/s.

Because slow slip events occur in subduction zones, their relationship to megathrust earthquakes is of economic, human, and scientific importance. The seismic hazard posed by ETS events is dependent on their focus. If the slow slip event extends into the seismogenic zone, accumulated stress would be released, decreasing the risk of a catastrophic earthquake. [8] [9] However, if the slow slip event occurs down-dip of the seismogenic zone, it may "load" the region with stress. [8] [10] The probability of a great earthquake (moment magnitude scale ) occurring has been suggested to be 30 times greater during an ETS event than otherwise, [11] but more recent observations have shown this theory to be simplistic. [12] One factor is that tremor occurs in many segments at different times along the plate boundary; another factor is that rarely have tremor and large earthquakes been observed to correlate in timing. [13]

Tremor

Slow slip events are frequently linked to non-volcanic seismological "rumbling", or tremor. Tremor is distinguished from earthquakes in several key respects: frequency, duration, and origin. Seismic waves generated by earthquakes are high-frequency and short-lived. These characteristics allow seismologists to determine the hypocentre of an earthquake using first-arrival methods. In contrast, tremor signals are weak and extended in duration. [14] Furthermore, while earthquakes are caused by the rupture of faults, tremor is generally attributed to underground movement of fluids (magmatic or hydrothermal). [15] As well as in subduction zones, tremor has been detected in transform faults such as the San Andreas. [16]

In both the Cascadia and Nankai subduction zones, slow slip events are directly associated with tremor. [4] [17] In the Cascadia subduction zone, slip events and seismological tremor signals are spatially and temporally coincident, [18] but this relationship does not extend to the Mexican subduction zone. [19] Furthermore, this association is not an intrinsic characteristic of slow slip events. In the Hikurangi Subduction Zone, New Zealand, episodic slip events are associated with distinct, reverse-faulted microearthquakes. [6]

Two types of tremor have been identified: one associated with geodetic deformation (as described above), and one associated with 5 to 10 second bursts excited by distant earthquakes. The second type of tremor has been detected worldwide; for example, it has been triggered in the San Andreas Fault by the 2002 Denali earthquake and in Taiwan by the 2001 Kunlun earthquake. [20] [21]

Geological interpretation

Tremor is commonly associated with the underground movement of magmatic or hydrothermal fluids. [15] As a plate is subducted into the mantle, it loses water from its porespace and due to phase changes of hydrous minerals (such as amphibole). It has been proposed that this liberation of water generates a supercritical fluid at the plate interface, lubricating plate motion. [22] This supercritical fluid may open fractures in the surrounding rock, and that tremor is the seismological signal of this process. [22] Mathematical modelling has successfully reproduced the periodicity of episodic tremor and slip in the Cascadia region by incorporating this dehydration effect. [23] In this interpretation, tremor may be enhanced where the subducting oceanic crust is young, hot, and wet as opposed to older and colder.

However, alternative models have also been proposed. Tremor has been demonstrated to be influenced by tides or variable fluid flow through a fixed volume. [8] [24] Tremor has also been attributed to shear slip at the plate interface. [4] Recent contributions in mathematical modelling reproduce the sequences of Cascadia and Hikurangi (New Zealand), and suggest in-situ dehydration as the cause for the episodic tremor and slip events. [25] [26] [27]

See also

Related Research Articles

<span class="mw-page-title-main">Intraplate earthquake</span> Earthquake that occurs within the interior of a tectonic plate

An intraplate earthquake is an earthquake that occurs in the interior of a tectonic plate, in contrast to an interplate earthquake on the boundary of a tectonic plate. It is also called an intraslab earthquake, especially when occurring in a microplate.

<span class="mw-page-title-main">Juan de Fuca Plate</span> Small tectonic plate in the eastern North Pacific

The Juan de Fuca Plate is a small tectonic plate (microplate) generated from the Juan de Fuca Ridge that is subducting beneath the northerly portion of the western side of the North American Plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted underneath the North American Plate.

<span class="mw-page-title-main">Cascadia subduction zone</span> Convergent plate boundary that stretches from northern Vancouver Island to Northern California

The Cascadia subduction zone is a 960 km (600 mi) fault at a convergent plate boundary, about 110–160 km (70–100 mi) off the Pacific coast, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30 m (98 ft). The Oregon Department of Emergency Management estimates shaking would last 5–7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American Plate. The zone varies in width and lies offshore beginning near Cape Mendocino, Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.

<span class="mw-page-title-main">Harmonic tremor</span> Sustained ground vibration associated with underground movement of magma or volcanic gas

A harmonic tremor is a sustained release of seismic and infrasonic energy typically associated with the underground movement of magma, the venting of volcanic gases from magma, or both. It is a long-duration release of seismic energy, with distinct spectral lines, that often precedes or accompanies a volcanic eruption. More generally, a volcanic tremor is a sustained signal that may or may not possess these harmonic spectral features. Being a long-duration continuous signal from a temporally extended source, a volcanic tremor contrasts distinctly with transient sources of seismic radiation, such as tremors that are typically associated with earthquakes and explosions.

An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other. The slipping process creates an earthquake with relative displacement on either side of the fault, resulting in seismic waves which travel through the Earth and along the Earth's surface. Relative plate motion can be lateral as along a transform fault boundary, vertical if along a convergent boundary or a divergent boundary, and oblique, with horizontal and lateral components at the boundary. Interplate earthquakes associated at a subduction boundary are called megathrust earthquakes, which include most of the Earth's largest earthquakes.

Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes.

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 slow earthquakes now appear to be accompanied by fluid flow and related tremor, which can be detected and approximately located using seismometer data filtered appropriately. That is, they are quiet compared to a regular earthquake, but not "silent" as described in the past.

<span class="mw-page-title-main">Okinawa Plate</span> Minor tectonic plate from the northern end of Taiwan to the southern tip of Kyūshū

The Okinawa Plate, or Okinawa Platelet, is a minor continental tectonic plate in the northern and eastern hemispheres stretching from the northern end of Taiwan to the southern tip of the island of Kyūshū. The Okinawa Plate hosts typical earthquakes, like the 1911 Kikai Island earthquake, and various types of slow earthquakes, including low frequency earthquakes, very low frequency earthquakes, tremor, and slow slip events.

The 1995 Antofagasta earthquake occurred on July 30 at 05:11 UTC with a moment magnitude of 8.0 and a maximum Mercalli intensity of VII. The Antofagasta Region in Chile was affected by a moderate tsunami, with three people killed, 58 or 59 injured, and around 600 homeless. Total damage from the earthquake and tsunami amounted to $1.791 million.

<span class="mw-page-title-main">1861 Sumatra earthquake</span> Natural disaster in Indonesia

The 1861 Sumatra earthquake occurred on 16 February and was the last in a sequences of earthquakes that ruptured adjacent parts of the Sumatran segment of the Sunda megathrust. It caused a devastating tsunami which led to several thousand fatalities. The earthquake was felt as far away as the Malay peninsula and the eastern part of Java. The rupture area for the 2005 Nias–Simeulue earthquake is similar to that estimated for the 1861 event.

<span class="mw-page-title-main">North Island Fault System</span> Fault zone of the east coast of New Zealands North Island

The North Island Fault System (NIFS) is a set of southwest–northeast trending seismically-active faults in the North Island of New Zealand that carry much of the dextral strike-slip component of the oblique convergence of the Pacific Plate with the Australian Plate. However despite at least 3 km (1.9 mi) of uplift of the axial ranges in the middle regions of the fault system during the last 10 million years most of the shortening on this part of the Hikurangi Margin is accommodated by subduction.

The 1935 Sumatra earthquake occurred at 09:35 local time on 28 December. It had a magnitude of Mw 7.7 and a maximum felt intensity of VII (Damaging) on the European macroseismic scale. It triggered a minor tsunami.

Susan Y. Schwartz is a scientist at the University of California, Santa Cruz known for her research on earthquakes, through field projects conducted in locations in Costa Rica and the San Andreas Fault.

The 1968 Hyūga-nada earthquake occurred on April 1 at 09:42 local time. The earthquake had a magnitude of Mw 7.5, and the epicenter was located in Hyūga-nada Sea, off the islands of Kyushu and Shikoku, Japan. The magnitude of this earthquake was also given as MJMA 7.5. A tsunami was observed. One person was killed, and 22 people were reported injured. The intensity reached shindo 5 in Miyazaki and Kōchi.

The 1911 Guerrero earthquake occurred on December 16 at 12:14 local time near the coast of Guerrero, Mexico along the Mexican subduction zone. The earthquake's energy was calculated using several different magnitude scales with an estimated moment magnitude of 7.6 and a surface wave magnitude of 7.8. Following the event, telegraphy reports came in from a broad area of Mexico. Cities from Guadalajara, Mérida, and Tapachula all reported the tremors. The earthquake lasted over two minutes and resulted in the deaths of 28 people.

<span class="mw-page-title-main">Hikurangi Margin</span> Subduction zone off the east coast of New Zealands North Island

The Hikurangi Margin is New Zealand's largest subduction zone and fault.

<span class="mw-page-title-main">Laura Wallace</span> American geophysicist

Laura Martin Wallace is a geodetic principal scientist who works between the University of Texas at Austin and GNS Science in New Zealand. She was elected Fellow of the Royal Society Te Apārangi in 2018.

<span class="mw-page-title-main">2021 Chignik earthquake</span> 7th largest earthquake in the US

An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.

<span class="mw-page-title-main">Oblique subduction</span> Tectonic process

Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.

<span class="mw-page-title-main">Earthquake cycle</span> Natural phenomenon

The earthquake cycle refers to the phenomenon that earthquakes repeatedly occur on the same fault as the result of continual stress accumulation and periodic stress release. Earthquake cycles can occur on a variety of faults including subduction zones and continental faults. Depending on the size of the earthquake, an earthquake cycle can last decades, centuries, or longer. The Parkfield portion of the San Andreas fault is a well-known example where similarly located M6.0 earthquakes have been instrumentally recorded every 30–40 years.

References

  1. ↑ "Episodic Tremor and Slip beneath Vancouver Island". Natural Resources Canada. Archived from the original on 26 March 2010. Retrieved 17 June 2011.
  2. ↑ Obara, Kazushige (2002). "Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan". Science. 296 (5573): 1679–1681. Bibcode:2002Sci...296.1679O. doi:10.1126/science.1070378. PMID   12040191. S2CID   32354691.
  3. ↑ "Geodynamics – Episodic Tremor and Slip (ETS)". Natural Resources Canada – Geological Survey of Canada. Archived from the original on 4 June 2011. Retrieved 17 June 2011.
  4. 1 2 3 4 Rogers, G.; Dragert, H. (2003). "Episodic Tremor and Slip on the Cascadia Subduction Zone: The Chatter of Silent Slip". Science. 300 (5627): 1942–1943. Bibcode:2003Sci...300.1942R. doi: 10.1126/science.1084783 . PMID   12738870. S2CID   2672381.
  5. 1 2 3 Liu, Yajing; Rice, James R. (2009). "Slow slip predictions based on granite and gabbro friction data compared to GPS measurements in northern Cascadia". Journal of Geophysical Research. 114 (B9): B09407. Bibcode:2009JGRB..114.9407L. doi: 10.1029/2008JB006142 .
  6. 1 2 Delahaye, E.J.; Townend, J.; Reyners, M.E.; Rogers, G. (2009). "Microseismicity but no tremor accompanying slow slip in the Hikurangi subduction zone, New Zealand". Earth and Planetary Science Letters. 277 (1–2): 21–28. Bibcode:2009E&PSL.277...21D. doi:10.1016/j.epsl.2008.09.038.
  7. ↑ "'Silent' quake gently rocks Wellington". 3 News NZ . May 28, 2013. Archived from the original on August 23, 2014. Retrieved May 28, 2013.
  8. 1 2 3 Rubinstein, J., Shelly, D., Ellsworth, W. (2010), "Non-volcanic Tremor: A Window into the Roots of Fault Zones", in New Frontiers in Integrated Solid Earth Sciences, edited by S. Cloetingh and J. Negendank, pp. 287–314, Springer Science+Business Media B.V., doi : 10.1007/978-90-481-2737-5_8
  9. ↑ Kostoglodov, V.; Singh, S.; Santiago, J.; Franco, S.; Larson, K.; Lowry, A.; Bilham, R. (2003). "A large silent earthquake in the Guerrero seismic gap, Mexico". Geophysical Research Letters. 30 (15): 1807. Bibcode:2003GeoRL..30.1807K. doi: 10.1029/2003GL017219 .
  10. ↑ Brudzinski, M.; Cabral-Cano, E.; Correa-Mora, F.; Demets, C.; Márquez-Azúa, B. (2007). "Slow slip transients along the Oaxaca subduction segment from 1993 to 2007". Geophysical Journal International. 171 (2): 523–538. Bibcode:2007GeoJI.171..523B. doi: 10.1111/j.1365-246X.2007.03542.x .
  11. ↑ Mazzotti, S. (2004). "Variability of Near-Term Probability for the Next Great Earthquake on the Cascadia Subduction Zone". Bulletin of the Seismological Society of America. 94 (5): 1954–1959. Bibcode:2004BuSSA..94.1954M. doi:10.1785/012004032.
  12. ↑ Beroza, G. C.; Ide, S. (2011). "Non-Volcanic Tremor and Slow Earthquakes". Annu. Rev. Earth Planet. Sci. 39: 271–296. Bibcode:2011AREPS..39..271B. doi:10.1146/annurev-earth-040809-152531.
  13. ↑ Brudzinski, M.; Allen, R. (2007). "Segmentation in episodic tremor and slip all along Cascadia". Geology. 35 (10): 905–910. Bibcode:2007Geo....35..907B. doi:10.1130/G23740A.1. S2CID   6682060.
  14. ↑ Shelly, David R.; Beroza, Gregory C.; Ide, Satoshi (2007). "Non-volcanic tremor and low-frequency earthquake swarms". Nature. 446 (7133): 305–307. Bibcode:2007Natur.446..305S. doi:10.1038/nature05666. PMID   17361180. S2CID   4404016.
  15. 1 2 Schwartz, Susan Y.; Rokosky, Juliana M. (2007). "Slow slip events and seismic tremor at circum-Pacific subduction zones". Reviews of Geophysics. 45 (3): n/a. Bibcode:2007RvGeo..45.3004S. doi: 10.1029/2006RG000208 . S2CID   128205122.
  16. ↑ Nadeau, R. M.; Dolenc, D. (2005). "Nonvolcanic Tremors Deep Beneath the San Andreas Fault". Science. 307 (5708): 389. doi:10.1126/science.1107142. PMID   15591163. S2CID   32405993.
  17. ↑ Obara, Kazushige; Hirose, Hitoshi; Yamamizu, Fumio; Kasahara, Keiji (2004). "Episodic slow slip events accompanied by non-volcanic tremors in southwest Japan subduction zone". Geophysical Research Letters. 31 (23): L23602. Bibcode:2004GeoRL..3123602O. doi: 10.1029/2004GL020848 .
  18. ↑ Bartlow, Noel M.; Miyazaki, Shin'Ichi; Bradley, Andrew M.; Segall, Paul (2011). "Space-time correlation of slip and tremor during the 2009 Cascadia slow slip event". Geophysical Research Letters. 38 (18): n/a. Bibcode:2011GeoRL..3818309B. doi: 10.1029/2011GL048714 .
  19. ↑ Payero, Juan S.; Kostoglodov, Vladimir; Shapiro, Nikolai; Mikumo, Takeshi; Iglesias, Arturo; Pérez-Campos, Xyoli; Clayton, Robert W. (2008). "Nonvolcanic tremor observed in the Mexican subduction zone". Geophysical Research Letters. 35 (7): n/a. Bibcode:2008GeoRL..35.7305P. doi:10.1029/2007GL032877. hdl: 2433/193421 . S2CID   1039272.
  20. ↑ Peng, Zhigang; Vidale, John E.; Creager, Kenneth C.; Rubinstein, Justin L.; Gomberg, Joan; Bodin, Paul (2008). "Strong tremor near Parkfield, CA, excited by the 2002 Denali Fault earthquake". Geophysical Research Letters. 35 (23): L23305. Bibcode:2008GeoRL..3523305P. doi: 10.1029/2008GL036080 .
  21. ↑ Peng, Zhigang; Chao, Kevin (2008). "Non-volcanic tremor beneath the Central Range in Taiwan triggered by the 2001 Kunlun earthquake". Geophysical Journal International. 175 (2): 825–829. doi: 10.1111/j.1365-246X.2008.03886.x .
  22. 1 2 Obara, K. (2002). "Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan". Science. 296 (5573): 1679–1681. Bibcode:2002Sci...296.1679O. doi:10.1126/science.1070378. PMID   12040191. S2CID   32354691.
  23. ↑ Liu, Yajing; Rice, James R. (2007). "Spontaneous and triggered aseismic deformation transients in a subduction fault model". Journal of Geophysical Research. 112 (B9): B09404. Bibcode:2007JGRB..112.9404L. doi: 10.1029/2007JB004930 .
  24. ↑ Watanabe, Tomoko; Hiramatsu, Yoshihiro; Obara, Kazushige (2007). "Scaling relationship between the duration and the amplitude of non-volcanic deep low-frequency tremors". Geophysical Research Letters. 34 (7): L07305. Bibcode:2007GeoRL..34.7305W. doi: 10.1029/2007GL029391 . hdl: 2297/6771 .
  25. ↑ Alevizos, S.; Poulet, T.; Veveakis, E. (2014). "Thermo-poro-mechanics of chemically active creeping faults. 1: Theory and steady state considerations". Journal of Geophysical Research: Solid Earth. 119 (6): 4558–4582. Bibcode:2014JGRB..119.4558A. doi:10.1002/2013JB010070. hdl: 1959.4/unsworks_37157 . S2CID   128568799.
  26. ↑ Veveakis, E.; Poulet, T.; Alevizos, S. (2014). "Thermo-poro-mechanics of chemically active creeping faults: 2. Transient considerations". Journal of Geophysical Research: Solid Earth. 119 (6): 4583–4605. Bibcode:2014JGRB..119.4583V. doi: 10.1002/2013JB010071 .
  27. ↑ Poulet, T.; Veveakis, E.; Regenauer-Lieb, K.; Yuen, D. A. (2014). "Thermo-poro-mechanics of chemically active creeping faults: 3. The role of serpentinite in episodic tremor and slip sequences, and transition to chaos". Journal of Geophysical Research: Solid Earth. 119 (6): 4606–4625. Bibcode:2014JGRB..119.4606P. doi: 10.1002/2014JB011004 . hdl: 1959.4/unsworks_37156 .
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.