1981 Playa Azul earthquake
{{Infobox earthquake
| title = 1981 Playa Azul earthquake
| timestamp = 1981-10-25 03:22:15
| anss-url = usp0001gnv
| isc-event = 610441
| local-date = October 24, 1981
| local-time = 21:22
| map2 = {{Location map | Mexico
| label=
| lat=18.05
| long=-102.08
| mark=Bullseye1.png
| marksize=40
| position=top
| width= 250
| float=right
| caption=
|relief=yes}}
| magnitude = 7.2 {{M|w|link=y}}
7.3 {{M|s|link=y}}
| depth = 33 km
| location = {{coord|18.05|N|102.08|W}}
| countries affected = Mexico
| tsunami =
| aftershocks =
| intensity = {{MMI|8}}
| casualties = 3–9 killed, 28 injured
}}
The 1981 Playa Azul earthquake occurred on October 24, 1981, at 21:22 local time (03:22 UTC on October 25). It was located near Playa Azul, Michoacán, Mexico. The magnitude of the earthquake was {{M|w|link=y}} 7.2, or {{M|s|link=y}} 7.3.{{cite book|last=Engdahl |first=E.R. |author2=Villaseñor A. |title=International Handbook of Earthquake Engineering Seismology, Part A |editor=Lee W.H.K. |editor2=Kanamori H. |editor3=Jennings P. |editor4=Kissinger K. |publisher=International Association of Seismology and Physics of Earth's Interiors |year=2002 |volume=81A |pages=684 |chapter=Global seismicity: 1900–1999 |chapter-url=https://earthquake.usgs.gov/data/centennial/centennial.pdf}} Three deaths were reported, two from Michoacán and one from Mexico City. Some buildings were damaged in both Michoacán and Mexico City. A small tsunami was registered in Acapulco with a maximum height of 9 cm.{{Cite FTP |url=ftp://ftp.cicese.mx/pub/divOC/ocefisica/vientos/Tsunami_Links/Catalogo.pdf|title=Catalog of Tsunamis on the Western Coast of Mexico|last=Sanchez Devora|first=A.J.|author2=Farreras Sanz S.F.|year=1993|pages=36|server=SE-50|url-status=dead|accessdate=11 August 2012}}
Tectonic setting
The southwestern coast of Mexico lies above the convergent boundary where the Rivera plate and Cocos plate are being subducted beneath the North American plate along the Middle America Trench. The area is seismically very active with large thrust type earthquakes occurring along the plate interface and normal fault type earthquakes occurring at a somewhat deeper level within the descending slab. The plate interface seismicity in this area is strongly segmented, with separate Jalisco, Michoacán, Guerrero and Colima segments being recognised.{{cite journal|last=Pardo|first=M.|author2=Suárez G.|year=1995|title=Shape of the subducted Rivera and Cocos plates in southern Mexico: Seismic and tectonic implications|journal=Journal of Geophysical Research|volume=100|issue=B7|pages=12357–12373|url=http://www.geo.mtu.edu/EHaz/ConvergentPlatesClass/week%204/PardoSuarez95JB00919.pdf|accessdate=11 August 2012|doi=10.1029/95jb00919|bibcode=1995JGR...10012357P}} The southeastern end of the Michoacan segment coincides with the broad Orozco fracture zone within the Cocos plate.{{cite journal|last=Ramírez-Herrera|first=M.T.|author2=Kostoglodov V.|author3=Urrutia-Fucugauchi J.|name-list-style=amp|year=2011|title=Overview of Recent Coastal Tectonic Deformation in the Mexican Subduction Zone|journal=Pure and Applied Geophysics|volume=168|issue=8–9|pages=1415–1433|url=http://usuarios.geofisica.unam.mx/vladimir/papers_pdf/Ramirez_etal_PAGEOPH_2011.pdf|accessdate=11 August 2012|doi=10.1007/s00024-010-0205-y|bibcode=2011PApGe.168.1415R|s2cid=73715203}} During the 1970s, with no major earthquakes recorded since at least 1911, the segment was recognised as a major seismic gap.
Earthquake
This earthquake was an interplate earthquake that occurred in the central part of the Michoacán seismic gap.{{cite web|url=http://bibliotecadigital.ilce.edu.mx/sites/ciencia/volumen1/ciencia2/34/html/sec_12.html|title=Terremotos: Predicción|last=Nava|first=A.|work=La Ciencia para todos|language=Spanish|accessdate=11 August 2012}} The 1985 Michoacán earthquake broke the two remaining parts of the Michoacán gap, i.e. those to the north and south of the 1981 Playa Azul earthquake rupture zone.{{cite journal|last=Eissler|first=H.|author2=Astiz L.|author3=Kanamori H.|name-list-style=amp|year=1986|title=Tectonic setting and source parameters of the September 19, 1985 Michoacan, Mexican Earthquake|journal=Geophysical Research Letters|volume=13|issue=6|pages=569–572|url=http://www.gps.caltech.edu/uploads/File/People/kanamori/HKgrl86.pdf|accessdate=11 August 2012|doi=10.1029/gl013i006p00569|bibcode=1986GeoRL..13..569E|archive-url=https://web.archive.org/web/20100723150123/http://www.gps.caltech.edu/uploads/File/People/kanamori/HKgrl86.pdf|archive-date=2010-07-23|url-status=dead}} The 1981 Playa Azul earthquake had a focal mechanism of reverse faulting from a shallow-dipping thrust fault.{{cite journal|last=Havskov|first=J.|author2=Singh S.K.|author3=Nava E.|author4=Dominguez T.|author5=Rodriguez M.|name-list-style=amp|year=1983|title=Playa Azul, Michoacán, Mexico, earthquake of 25 October 1981 (Ms = 7.3)|journal=Bulletin of the Seismological Society of America|volume=73|issue=2|pages=449–457|url=http://bssa.geoscienceworld.org/content/73/2/449.short|accessdate=11 August 2012}} The maximum slip of this earthquake was estimated to be about 4.04 m.{{cite web|url=http://www.geociencias.unam.mx/~cmendoza/FINAL_PAGINA_WEB_20_06_2012/25-10-1981/SLIP_PLAYA_AZUL.html|title=Playa Azul Slip|last=Lopez|first=M.R.M.|publisher=Centro de Geociencias|language=Spanish|accessdate=11 August 2012|archive-url=https://web.archive.org/web/20131215001736/http://www.geociencias.unam.mx/~cmendoza/FINAL_PAGINA_WEB_20_06_2012/25-10-1981/SLIP_PLAYA_AZUL.html|archive-date=15 December 2013|url-status=dead}} According to the calculation of C. Mendoza, along the dipping interface the area of maximum slip was concentrated below the hypocenter, and there was another area of significant slip, of about {{convert|1|m|ft}}, above the hypocenter.{{cite journal|last=Santoyo|first=M.A.|author2=Mikumo T.|author3=Mendoza C.|name-list-style=amp|year=2007|title=Possible lateral stress interactions in a sequence of large interplate earthquakes on the subducting Cocos and Rivera Plates|journal=Geofísica Internacional|volume=46|issue=4|pages=211–226|doi=10.22201/igeof.00167169p.2007.46.4.50|url=https://www.redalyc.org/pdf/568/56846401.pdf|accessdate=11 August 2012|doi-access=free}}
Damage
Michoacan suffered widespread damage with some buildings also affected in Mexico City. There were 2 deaths and 17 people injured in Michoacán and 1 death and 11 people injured in Mexico City.{{cite web|url=https://earthquake.usgs.gov/earthquakes/eqarchives/significant/sig_1981.php |title=Significant Earthquakes of the World 1981 |publisher=United States Geological Survey |date=January 5, 2010 |accessdate=11 August 2012 |url-status=dead |archiveurl=https://web.archive.org/web/20121011191203/http://earthquake.usgs.gov/earthquakes/eqarchives/significant/sig_1981.php |archivedate=11 October 2012 }} One source reports a total of 9 deaths associated with this earthquake.{{cite web|url=http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=4932&t=101650&s=13&d=22,26,13,12&nd=display|archive-url=https://archive.today/20121213225434/http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=4932&t=101650&s=13&d=22,26,13,12&nd=display|url-status=dead|archive-date=December 13, 2012|title=Significant Earthquake|publisher=National Geophysical Data Center|author-link=National Geophysical Data Center|accessdate=11 August 2012}}
Power outages and telephone service interruptions were widespread in Mexico City.{{cite news|url=https://www.nytimes.com/1981/10/25/world/earthquake-hits-mexico-city-power-outages-widespread.html|title=Earthquake Hits Mexico City; Power Outages Widespread|agency=Associated Press|date=October 5, 1981|work=The New York Times|accessdate=11 August 2012}} Thousands of people got stuck in darkness in the Mexico City Metro.http://digaohm.semar.gob.mx/imagenes/CAT/Historia_tsunamis.pdf{{Dead link|date=August 2018 |bot=InternetArchiveBot |fix-attempted=yes }}
See also
References
{{reflist}}
External links
- {{EQ-isc-link|610441}}
{{Earthquakes in 1981}}
{{Earthquakes in Mexico}}
Category:Earthquakes in Mexico