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 Playa Azul (en: ''Blue Beach'') may refer to: Places * Playa Azul (Michoacán), beach town in Michoacán, Mexico * Playa Azul (Oaxaca), town in the municipality of Salina Cruz, Oaxaca, Mexico * , town in Colonia department, Uruguay * Playa Azul, ...

Michoacán Michoacán, formally Michoacán de Ocampo, officially the Free and Sovereign State of Michoacán de Ocampo, is one of the 31 states which, together with Mexico City, compose the Political divisions of Mexico, Federal Entities of Mexico. The stat ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

. The magnitude of the earthquake was 7.2, or 7.3. Three deaths were reported, two from Michoacán and one from

Mexico City Mexico City is the capital city, capital and List of cities in Mexico, largest city of Mexico, as well as the List of North American cities by population, most populous city in North America. It is one of the most important cultural and finan ...

. Some buildings were damaged in both Michoacán and Mexico City. A small tsunami was registered in

Acapulco Acapulco de Juárez (), commonly called Acapulco ( , ; ), is a city and Port of Acapulco, major seaport in the Political divisions of Mexico, state of Guerrero on the Pacific Coast of Mexico, south of Mexico City. Located on a deep, semicirc ...

with a maximum height of 9 cm.

Tectonic setting

The southwestern coast of Mexico lies above the

convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

where the

Rivera plate The Rivera plate is a small tectonic plate (a microplate) located off the west coast of Mexico, just south of the Baja California peninsula. It is bounded on the northwest by the East Pacific Rise, on the southwest by the Rivera Transform Fa ...

and Cocos plate are being

subducted Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second plat ...

beneath the North American plate along the

Middle America Trench The Middle America Trench is a major subduction zone, an oceanic trench in the eastern Pacific Ocean off the southwestern coast of Middle America, stretching from central Mexico to Costa Rica. The trench is 1,700 miles (2,750 km) long an ...

. 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. The southeastern end of the Michoacan segment coincides with the broad Orozco

fracture zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

within the Cocos plate. During the 1970s, with no major earthquakes recorded since at least 1911, the segment was recognised as a major

seismic gap A seismic gap is a segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long time, compared with other segments along the same structure. There is a hypothesis or theory that states that over long ...

Earthquake

This earthquake was an

interplate earthquake An interplate earthquake 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 ...

that occurred in the central part of the Michoacán seismic gap. 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. The 1981 Playa Azul earthquake had a

focal mechanism The focal mechanism of an earthquake describes the Fault (geology)#Slip.2C heave.2C throw, deformation in the Hypocenter, source region that generates the seismic waves. In the case of a Fault (geology), fault-related event, it refers to the ori ...

of reverse faulting from a shallow-dipping

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. I ...

. The maximum slip of this earthquake was estimated to be about 4.04 m. 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 , above the hypocenter.

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. One source reports a total of 9 deaths associated with this earthquake. Power outages and telephone service interruptions were widespread in Mexico City. Thousands of people got stuck in darkness in the

Mexico City Metro The Mexico City Metro () is a rapid transit system that serves Greater Mexico City, the metropolitan area of Mexico City, including some municipalities in the State of Mexico. Operated by the Sistema de Transporte Colectivo (STC), it is the Lis ...

.http://digaohm.semar.gob.mx/imagenes/CAT/Historia_tsunamis.pdf

References

External links

* {{Earthquakes in Mexico Playa Azul earthquake, 1981 Earthquakes in Mexico 1981 in Mexico 1980s tsunamis October 1981 in Mexico 1981 disasters in Mexico

Tectonic setting

Earthquake

Damage

See also

References

External links