1981_Playa_Azul_earthquake Knowpia

1981 Playa Azul earthquake
UTC time	1981-10-25 03:22:15
ISC event	610441
USGS-ANSS	ComCat
Local date	October 24, 1981
Local time	21:22
Magnitude	7.2 Mw; 7.3 Ms
Depth	33 km
Epicenter	18°03′N 102°05′W / 18.05°N 102.08°W
Areas affected	Mexico
Max. intensity	MMI VIII (Severe)
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 7.2, or M_s 7.3.^[1] 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.^[2]

Tectonic setting edit

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.^[3] The southeastern end of the Michoacan segment coincides with the broad Orozco fracture zone within the Cocos Plate.^[4] During the 1970s, with no major earthquakes recorded since at least 1911, the segment was recognised as a major seismic gap.^[5]

Earthquake edit

This earthquake was an interplate earthquake that occurred in the central part of the Michoacán seismic gap.^[6] 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.^[5] The 1981 Playa Azul earthquake had a focal mechanism of reverse faulting from a shallow-dipping thrust fault.^[7] The maximum slip of this earthquake was estimated to be about 4.04 m.^[8] 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 1 metre (3.3 ft), above the hypocenter.^[9]

Damage edit

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.^[10] One source reports a total of 9 deaths associated with this earthquake.^[11]

Power outages and telephone service interruptions were widespread in Mexico City.^[12] Thousands of people got stuck in darkness in the Mexico City Metro.^[13]

References edit

^ Engdahl, E.R.; Villaseñor A. (2002). "Global seismicity: 1900–1999" (PDF). In Lee W.H.K.; Kanamori H.; Jennings P.; Kissinger K. (eds.). International Handbook of Earthquake Engineering Seismology, Part A. Vol. 81A. International Association of Seismology and Physics of Earth's Interiors. p. 684.
^ Sanchez Devora, A.J.; Farreras Sanz S.F. (1993). "Catalog of Tsunamis on the Western Coast of Mexico" (PDF). SE-50. World data Center A for Solid Earth Geophsics. p. 36. Retrieved 11 August 2012.
^ Pardo, M.; Suárez G. (1995). "Shape of the subducted Rivera and Cocos plates in southern Mexico: Seismic and tectonic implications" (PDF). Journal of Geophysical Research. 100 (B7): 12357–12373. Bibcode:1995JGR...10012357P. doi:10.1029/95jb00919. Retrieved 11 August 2012.
^ Ramírez-Herrera, M.T.; Kostoglodov V. & Urrutia-Fucugauchi J. (2011). "Overview of Recent Coastal Tectonic Deformation in the Mexican Subduction Zone" (PDF). Pure and Applied Geophysics. 168 (8–9): 1415–1433. Bibcode:2011PApGe.168.1415R. doi:10.1007/s00024-010-0205-y. S2CID 73715203. Retrieved 11 August 2012.
^ ^a ^b Eissler, H.; Astiz L. & Kanamori H. (1986). "Tectonic setting and source parameters of the September 19, 1985 Michoacan, Mexican Earthquake" (PDF). Geophysical Research Letters. 13 (6): 569–572. Bibcode:1986GeoRL..13..569E. doi:10.1029/gl013i006p00569. Archived from the original (PDF) on 2010-07-23. Retrieved 11 August 2012.
^ Nava, A. "Terremotos: Predicción". La Ciencia para todos (in Spanish). Retrieved 11 August 2012.
^ Havskov, J.; Singh S.K.; Nava E.; Dominguez T. & Rodriguez M. (1983). "Playa Azul, Michoacán, Mexico, earthquake of 25 October 1981 (Ms = 7.3)". Bulletin of the Seismological Society of America. 73 (2): 449–457. Retrieved 11 August 2012.
^ Lopez, M.R.M. "Playa Azul Slip" (in Spanish). Centro de Geociencias. Archived from the original on 15 December 2013. Retrieved 11 August 2012.
^ Santoyo, M.A.; Mikumo T. & Mendoza C. (2007). "Possible lateral stress interactions in a sequence of large interplate earthquakes on the subducting Cocos and Rivera Plates" (PDF). Geofísica Internacional. 46 (4): 211–226. doi:10.22201/igeof.00167169p.2007.46.4.50. Retrieved 11 August 2012.
^ United States Geological Survey (January 5, 2010). "Significant Earthquakes of the World 1981". Archived from the original on 11 October 2012. Retrieved 11 August 2012.
^ National Geophysical Data Center. "Significant Earthquake". Retrieved 11 August 2012.
^ "Earthquake Hits Mexico City; Power Outages Widespread". The New York Times. Associated Press. October 5, 1981. Retrieved 11 August 2012.
^ http://digaohm.semar.gob.mx/imagenes/CAT/Historia_tsunamis.pdf^{[permanent dead link]}