Tsunami earthquake explained

In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanamori in 1972. Such events are a result of relatively slow rupture velocities. They are particularly dangerous as a large tsunami may arrive at a coastline with little or no warning.

Characteristics

The distinguishing feature for a tsunami earthquake is that the release of seismic energy occurs at long periods (low frequencies) relative to typical tsunamigenic earthquakes. Earthquakes of this type do not generally show the peaks of seismic wave activity associated with ordinary events. A tsunami earthquake can be defined as an undersea earthquake for which the surface wave magnitude M_s differs markedly from the moment magnitude M_w, because the former is calculated from surface waves with a period of about 20 seconds, whereas the latter is a measure of the total energy release at all frequencies.^[1] The displacements associated with tsunami earthquakes are consistently greater than those associated with ordinary tsunamigenic earthquakes of the same moment magnitude, typically more than double. Rupture velocities for tsunami earthquakes are typically about 1.0 km per second, compared to the more normal 2.5 - 3.5 km per second for other megathrust earthquakes. These slow rupture speeds lead to greater directivity, with the potential to cause higher run-ups on short coastal sections. Tsunami earthquakes mainly occur at subduction zones where there is a large accretionary wedge or where sediments are being subducted, as this weaker material leads to the slower rupture velocities.^[1]

Cause

Analysis of tsunami earthquakes such as the 1946 Aleutian Islands earthquake shows that the release of seismic moment takes place at an unusually long period. Calculations of the effective moment derived from surface waves show a rapid increase with decrease in the frequency of the seismic waves, whereas for ordinary earthquakes it remains almost constant with frequency. The duration over which the seabed is deformed has little effect on the size of the resultant tsunami for times up to several minutes. The observation of long period energy release is consistent with unusually slow rupture propagation velocities.^[2] Slow rupture velocities are linked to propagation through relatively weak material, such as poorly consolidated sedimentary rocks. Most tsunami earthquakes have been linked to rupture within the uppermost part of a subduction zone, where an accretionary wedge is developed in the hanging wall of the megathrust. Tsunami earthquakes have also been linked to the presence of a thin layer of subducted sedimentary rock along the uppermost part of the plate interface, as is thought to be present in areas of significant topography at the top of the oceanic crust, and where propagation was in an up-dip direction, possibly reaching the seafloor.^[3]

Identifying tsunami earthquakes

Standard methods of giving early warnings for tsunamis rely on data that will not typically identify a tsunami earthquake as tsunamigenic and therefore fail to predict possibly damaging tsunamis.^[4]

Examples

1896 Sanriku

See main article: 1896 Sanriku earthquake. On 15 June 1896 the Sanriku coast was struck by a devastating tsunami with a maximum wave height of 38.2 m, which caused more than 22,000 deaths. The residents of the coastal towns and villages were taken completely by surprise because the tsunami had only been preceded by a relatively weak shock. The magnitude of the tsunami has been estimated as M_t=8.2 while the earthquake shaking only indicated a magnitude of M_s=7.2. This discrepancy in magnitude requires more than just a slow rupture velocity. Modelling of tsunami generation that takes into account additional uplift associated with deformation of the softer sediments of the accretionary wedge caused by horizontal movement of the 'backstop' in the overriding plate has successfully explained the discrepancy, estimating a magnitude of M_w=8.0 - 8.1.^[5]

1992 Nicaragua

See main article: 1992 Nicaragua earthquake. The 1992 Nicaragua earthquake was the first tsunami earthquake to be recorded with a broad-band seismic network.^[6]

Other tsunami earthquakes

• 1605 Nankai earthquake^[7]
• 1677 Bōsō earthquake^[8]
• 1771 Great Yaeyama earthquake^[9]
• 1791 Okinawa earthquake^[10]
• 1907 Sumatra earthquake^{[11] [12]}
• April 1923 Kamchatka earthquake and tsunami^[13]
• 1934 Santa Cruz earthquake^[14]
• 1932 Jalisco earthquakes^[15]
• 1946 Aleutian Islands earthquake^[2]
• November 1960 Peru earthquake^[1]
• 1963 Kuril Islands earthquake^[1]
• 1975 Kuril Islands earthquake^[1]
• 1982 Tonga earthquake^[16]
• 1994 Java earthquake^[1]
• 1996 Chimbote earthquake^[3]
• 2002 Guerrero earthquake — A 6.7 earthquake off the coast of Mexico failed to trigger country's earthquake warning system due to its extremely low peak acceleration. The near-trench earthquake ruptured the Guerrero Gap and may have generated an anomalously large tsunami.^[17]
• 2006 Pangandaran earthquake and tsunami^[18]
• 2010 Mentawai earthquake and tsunami^[19]
• 2012 El Salvador earthquake^[20]
• 2015 Torishima earthquake — A moderate 5.7 earthquake near Tori-shima generated waves with a maximum amplitude of 0.5 meters at Hachijō-jima.^[21]
• 2021 South Sandwich Islands earthquakes^[22]

See also

• Kaikoura Canyon landslide tsunami hazard

Notes and References

1. Book: Bryant, E.. Tsunami: the underrated hazard. https://books.google.com/books?id=6lvl6i7r2CcC&pg=PA131. 19 July 2011. 2. 2008. Springer. 978-3-540-74273-9. 129 - 138. 5. Earthquake-generated tsunami.
2. Kanamori. H.. 1972. Mechanism of tsunami earthquakes. Physics of the Earth and Planetary Interiors. 6. 5. 346–359. 19 July 2011. 1972PEPI....6..346K. 10.1016/0031-9201(72)90058-1. 14 June 2011. https://web.archive.org/web/20110614131951/http://www.gps.caltech.edu/uploads/File/People/kanamori/HKpepi72c.pdf. dead.
3. Polet. J.. Kanamori H. . 2000. Shallow subduction zone earthquakes and their tsunamigenic potential. Geophysical Journal International. 142. 3. 684–702. 2000GeoJI.142..684P . 10.1046/j.1365-246X.2000.00205.x . free.
4. Tsuboi. S.. 2000. Application of M_wp to tsunami earthquake. Geophysical Research Letters. 27. 19. 3105. 10.1029/2000GL011735. 2000GeoRL..27.3105T. free.
5. Tanioka. Y.. Seno T.. 2001. Sediment effect on tsunami generation of the 1896 Sanriku tsunami earthquake. Geophysical Research Letters. 28. 17. 3389–3392. 19 July 2011. 10.1029/2001GL013149. 2001GeoRL..28.3389T. 56014660. 10 June 2011. https://web.archive.org/web/20110610231703/http://www.eri.u-tokyo.ac.jp/seno/Papers/2001GL013149.pdf. dead.
6. Kanamori. H.. Kikuchi M.. 1993. The 1992 Nicaragua earthquake: a slow tsunami earthquake associated with subducted sediments. Nature. 361. 6414. 714–716. 19 July 2011. 10.1038/361714a0. 1993Natur.361..714K. 4322936. 19 March 2012. https://web.archive.org/web/20120319210834/http://www.gps.caltech.edu/uploads/File/People/kanamori/HKnat93.pdf. dead.
7. Ishibashi. K.. 2004. Status of historical seismology in Japan. Annals of Geophysics. 47. 2/3. 339–368. 22 November 2009.
8. Yanagisawa . H. . Goto . K. . Sugawara . D. . Kanamaru . K. . Iwamoto . N. . Takamori . Y. . 2016 . Tsunami earthquake can occur elsewhere along the Japan Trench—Historical and geological evidence for the 1677 earthquake and tsunami . Journal of Geophysical Research: Solid Earth . 121 . 5 . 10.1002/2015JB012617. free . 2016JGRB..121.3504Y . 3504–3516 .
9. Nakamura . M. . Fault model of the 1771 Yaeyama earthquake along the Ryukyu Trench estimated from the devastating tsunami . Geophysical Research Letters . 2009 . 36 . 19 . L19307 . 10.1029/2009GL039730 . 2009GeoRL..3619307N .
10. Nakamura . M. . The 1768 and 1791 Okinawa tsunamis in the Ryukyu Trench region . Fall Meeting 2013 . 2013 . 2013 . . 2013AGUFM.T13E2574N.
11. Lee . William H. K. . William H. K. Lee . Rivera . Luis . Kanamori . Hiroo . 2010-10-01 . Historical seismograms for unravelling a mysterious earthquake: The 1907 Sumatra Earthquake . Geophysical Journal International . en . 183 . 1 . 358–374 . 2010GeoJI.183..358K . 10.1111/j.1365-246X.2010.04731.x . 0956-540X . free.
12. Martin. Stacey Servito. Li. Linlin. Okal. Emile A.. Morin. Julie. Tetteroo. Alexander E. G.. Switzer. Adam D.. Sieh. Kerry E.. 2019-03-26. Reassessment of the 1907 Sumatra "Tsunami Earthquake" Based on Macroseismic, Seismological, and Tsunami Observations, and Modeling. Pure and Applied Geophysics. 176. 7. 2831–2868. en. 10.1007/s00024-019-02134-2. 1420-9136. 2019PApGe.176.2831M. 10356/136833. 135197944. free.
13. Salaree, A., Okal, E.A. . The "Tsunami Earthquake" of 13 April 1923 in Northern Kamchatka: Seismological and Hydrodynamic Investigations . Pure and Applied Geophysics . 2017 . 175 . 4 . 1257–1285 . 10.1007/s00024-017-1721-9 . 134560632 . 5 June 2021.
14. Emile A. Okal . Nooshin Saloor . Historical tsunami earthquakes in the Southwest Pacific: an extension to Δ > 80° of the energy-to-moment parameter Θ . . 2017 . 210 . 2 . 852–873 . 10.1093/gji/ggx197 . free .
15. Okal E.A. . Borrero J.C. . The 'tsunami earthquake' of 1932 June 22 in Manzanillo, Mexico: seismological study and tsunami simulations . Geophysical Journal International . 2011 . 187 . 3 . 1443–1459 . 10.1111/j.1365-246X.2011.05199.x. 2011GeoJI.187.1443O . free .
16. Paul R. Lundgren . Emile A. Okal . Douglas A. Wiens . Rupture characteristics of the 1982 Tonga and 1986 Kermadec earthquakes . Journal of Geophysical Research: Solid Earth . 10 November 1989 . 94 . B11 . 15521–15539 . 10.1029/JB094iB11p15521. 1989JGR....9415521L .
17. Iglesias . A. . Singh . S. K. . Pacheco . J. F. . Alcántara . L. . Ortiz . M. . Ordaz . M. . Near-Trench Mexican Earthquakes Have Anomalously Low Peak Accelerations . Bulletin of the Seismological Society of America . 2003 . 93 . 2 . 953–959 . 10.1785/0120020168. 2003BuSSA..93..953I .
18. Ammon. C.J.. Kanamori H.. Lay T.. Velasco A.A.. 2006. The 17 July 2006 Java tsunami earthquake. Geophysical Research Letters. 33. 24. L24308. 10.1029/2006GL028005. 2006GeoRL..3324308A. free.
19. Hill E.M. . Borrero J.C. . Huang Z. . Qiu Q. . Banarjee B. . Natawidjaja D.H. . Danny Hilman Natawidjaja . Elosegui P. . Fritz H.M. . . The 2010 Mw 7.8 Mentawai earthquake: Very shallow source of a rare tsunami earthquake determined from tsunami field survey and near-field GPS data . Journal of Geophysical Research: Solid Earth . 117 . B6 . 10.1029/2012JB009159. 2012 . n/a . 2012JGRB..117.6402H . 10261/87207 . free .
20. Ye, Lingling; Lay, Thorne; Kanamori, Hiroo . Large earthquake rupture process variations on the Middle America megathrust . Earth and Planetary Science Letters . 2013 . 381 . 147–155 . 10.1016/j.epsl.2013.08.042 . 21 April 2021 . 2013E&PSL.381..147Y.
21. Osamu Sandanbata, Shingo Watada, Kenji Satake, Yoshio Fukao, Hiroko Sugioka, Aki Ito & Hajime Shiobara . Source Amplitude Estimation Based on Green's Law: Application to the 2015 Volcanic Tsunami Earthquake Near Torishima, South of Japan . Pure and Applied Geophysics . 2018 . 175 . 1371–1385 . 10.1007/s00024-017-1746-0 . 135266645 . 4 June 2021.
22. Zhe Jia . Zhan Zhongwen . . The 2021 South Sandwich Island Mw 8.2 earthquake: a slow event sandwiched between regular ruptures . Geophysical Research Letters . 2021 . 49 . 3 . Art. No. e2021GL097104 . 10.1002/essoar.10508921.1 . Caltech Library. 2022GeoRL..4997104J . 244736464 .