The 1979 Petatlán earthquake, also known as the IBERO earthquake occurred on March 14 at 05:07 local time in the Mexican state of

Guerrero Guerrero, officially the Free and Sovereign State of Guerrero, is one of the 32 states that compose the administrative divisions of Mexico, 32 Federal Entities of Mexico. It is divided into Municipalities of Guerrero, 85 municipalities. The stat ...

. The earthquake had a

surface-wave magnitude The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This mag ...

of 7.6 or

moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mwg, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. was defined in a 1979 paper ...

of 7.4 and maximum

Modified Mercalli intensity The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or ...

of VIII (''Severe''). The

epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...

, onshore, was located 12 km south southeast of Vallecitos de Zaragoza. With a shallow

hypocenter A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its ...

depth of 18.5 km, the earthquake caused extensive and widespread damage in

, including the near total destruction of campus buildings at

Universidad Iberoamericana The Ibero-American University (), also referred to by its acronym ''UIA'' but commonly known as ''Ibero'' or ''La Ibero'', is a private, Catholic, Mexican higher education institution, sponsored by the Mexican province of the Society of Jesus ( ...

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 ...

. Five people died and 35 others were injured due to the earthquake. The earthquake was felt in the states of

Jalisco Jalisco, officially the Free and Sovereign State of Jalisco, is one of the 31 states which, along with Mexico City, comprise the 32 Political divisions of Mexico, Federal Entities of Mexico. It is located in western Mexico and is bordered by s ...

and

Puebla Puebla, officially the Free and Sovereign State of Puebla, is one of the 31 states that, along with Mexico City, comprise the Federal Entities of Mexico. It is divided into 217 municipalities and its capital is Puebla City. Part of east-centr ...

, where damage was reported.

Tectonic setting

Mexico is one of the most seismically active regions in the world; located at the boundary of at least three tectonic plates. The west coast of Mexico lies at a

convergent plate 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 ...

between the Cocos plate and North American plate. The Cocos plate consisting of denser oceanic

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

, subducts beneath the less dense continental crust of the North American plate. Most of the Mexican landmass is situated on the North American plate moving westward. Because the oceanic crust is relatively dense, when the bottom of the Pacific Ocean meets the lighter continental crust of the Mexican landmass, the ocean floor subducts beneath the North American plate creating 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 ...

along the southern coast of Mexico. Occasionally, the contact interface or subduction zone megathrust release elastic strain during earthquakes. Large and sudden uplift of the seafloor can produce large

tsunamis A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, la ...

when such earthquakes occur.

Earthquake

The earthquake occurred as a result of

thrust faulting 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. If ...

due to a rupture on the

subduction 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 p ...

zone near the west coast of Mexico. The 7.6 earthquake was the largest subduction zone thrust event in the region since 1943. The quake partially ruptured the Guerrero gap; a

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 ...

on the subduction one that is capable of an earthquake of magnitude 8.0 or greater. Modelling of the finite fault suggest a rupture patch measuring 120 km by 120 km on the megathrust, involving two

asperities In materials science, asperity, defined as "unevenness of surface, roughness, ruggedness" (from the Latin ''asper''—"rough"), has implications (for example) in physics and seismology. Smooth surfaces, even those polished to a mirror finish, ar ...

. Slip on the megathrust occurred at depths ranging between 3–25 km. Inversion of

P-wave A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...

data revealed a limited area where the slip was 0.7 meters, while the peak slip was 1.19 meters. The rupture zone of the 1979 earthquake is located immediately southeast of that of the

1985 Mexico City earthquake The 1985 Mexico City earthquake struck in the early morning of 19 September at 07:17:50 (CST) with a Moment magnitude scale, moment magnitude of 8.0 and a maximal Modified Mercalli intensity scale, Mercalli intensity of IX (''Violent''). The ev ...

. Another magnitude 7.6 quake, the aftershock of the 1985 quake, ruptured the shallow section of the megathrust, up-dip of the 1979 quake.

Tsunami

A weak

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

with a maximum height of 1.3 meters was generated. The tsunami was also recorded on ocean bottom tide gauges in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

near the epicenter of the quake.

Impact

Substantial damage was reported in

. The earthquake severely damaged and collapsed two buildings in the

Ibero-American University The Ibero-American University (), also referred to by its acronym ''UIA'' but commonly known as ''Ibero'' or ''La Ibero'', is a private, Catholic, Mexican higher education institution, sponsored by the Mexican province of the Society of Jesus (Je ...

compound. Nine structures suffered serious damage and 25 had significant damage. Despite the collapse, there were no casualties as it did not occur during school hours. In total, 90% of structures in the university was affected by the tremor. At the time of the quake, an estimated 7,200 students were enrolled in the university. Scheduled lessons resumed on 22 March 1979 at the National Polytechnic Institute College of Engineering and Physical-Mathematic Sciences, which was undamaged. Water supply was disrupted by the earthquake, which left many residents without access to water for 48 hours. A total of 600 structures, including homes, cinemas, and other public infrastructures were damaged in the city. The earthquake had a maximum Mercalli intensity of VIII (''Severe'') recorded in

Chilpancingo Chilpancingo de los Bravo (commonly shortened to Chilpancingo; ; Nahuatl: Chilpantzinco ()) is the capital and second-largest city of the Mexican state of Guerrero. In 2010 it had a population of 187,251 people. The municipality has an area of ...

. The city suffered significant damage in the downtown area. A seven-story

reinforced concrete Reinforced concrete, also called ferroconcrete or ferro-concrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ...

building was demolished due to the severe damage it sustained during the quake. In

Petatlán Petatlán is a city in the municipality of Petatlán located along the Pacific Coast of the Mexican state of Guerrero. It is part of the Costa Grande region between Zihuatanejo and Acapulco. The city is known for the Sanctuary of the Padre Jes ...

, Guerrero, the earthquake destroyed some adobe styled homes.

Tectonic setting

Earthquake

Tsunami

Impact

See also

References

Further reading