On January 30, 1973, at 15:01 ( UTC–6), a magnitude 7.6

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

struck beneath the

Sierra Madre del Sur The Sierra Madre del Sur is a mountain range in southern Mexico, extending from southern Michoacán east through Guerrero, to the Isthmus of Tehuantepec in eastern Oaxaca. Geography The Sierra Madre del Sur joins with the Eje Volcánico Transv ...

range in the

Mexican Mexican may refer to: Mexico and its culture *Being related to, from, or connected to the country of Mexico, in North America ** People *** Mexicans, inhabitants of the country Mexico and their descendants *** Mexica, ancient indigenous people ...

states of Colima,

Jalisco Jalisco (, , ; Nahuatl: Xalixco), officially the Free and Sovereign State of Jalisco ( es, Estado Libre y Soberano de Jalisco ; Nahuatl: Tlahtohcayotl Xalixco), is one of the 31 states which, along with Mexico City, comprise the 32 Federal En ...

and

Michoacán Michoacán, formally Michoacán de Ocampo (; Purépecha: ), officially the Free and Sovereign State of Michoacán de Ocampo ( es, Estado Libre y Soberano de Michoacán de Ocampo), is one of the 32 states which comprise the Federal Entities of ...

. On the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

, the earthquake reached a maximum intensity of X (''Extreme''), causing serious damage in the region. At least 56 people were killed and about 390 were injured. The event is commonly referred to as the Colima earthquake.

Tectonic setting

Off the west coast of Mexico is 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 ...

; 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 ...

where the Cocos and

Rivera Rivera () is the capital of Rivera Department of Uruguay. The border with Brazil joins it with the Brazilian city of Santana do Livramento, which is only a street away from it, at the north end of Route 5. Together, they form an urban area of aro ...

plates

subducts Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

beneath the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacific ...

at a rate of ~6-9 cm/yr. The interface of this plate boundary is a huge

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. If ...

known as a megathrust which occasionally produces large megathrust earthquakes and

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) 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 other underwater explo ...

Earthquake

The January 30 earthquake ruptured a shallow-angle section of the megathrust near a

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can b ...

with the Rivera Plate. Its location places it very close to the rupture patch of the 1941 earthquake. The depth of the event varies between seismological agencies and studies, from as shallow as to . It is estimated that a by section of the subduction zone was involved in the rupture which propagated at a velocity of /s. The rupture occurred on the subduction interface at between and depth. Prior to the earthquake, that section of the subduction zone was designated a seismic gap which has not experience any earthquakes in recent memory. The 1985 Mexico City earthquake rupture would overlap that of the 1973 quake 12 years later. Around 330

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

s were recorded over a two-and-a-half week period following the deployment of

seismograph A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The output ...

s four days after the mainshock. The largest aftershock measured magnitude 6.2. Most of the aftershocks measured 1.5–4.5 on the local magnitude scale with focal depths of .

Tsunami

A moderate

with amplitudes of was observed along the Mexican coast. Tidal gauges in

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

also recorded the tsunami at .

Impact

The earthquake was powerful enough to be felt across the country to the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

. Severe shaking and heavy damage were limited to the states of Colima, Jalisco and Michoacán. Fifty six people died and 390 were injured by this event.

Tecomán Tecomán is a city and seat of the municipality of Tecomán in the Mexican state of Colima Colima (), officially the Free and Sovereign State of Colima ( es, Estado Libre y Soberano de Colima), is one of the 31 states that make up the 32 Fe ...

and

Coahuayana Coahuayana is a municipality located in the southwest region of the Mexican state of Michoacán. The municipality has an area of 362.34 square kilometres (0.61% of the surface of the state)

suffered significant damage from the violent ground motions. Landslides and ground fissures were discovered along the relatively unpopulated coasts of Michoacán. Water, electricity and telephone lines were cut throughout. An elementary school in Manzanillo, Colima sustained significant structural damage after the quake. The school building rocked so violently that many eyewitnesses thought the structure would collapse. Damage was so severe that the building was determined unsafe for use and demolished. In another partof the city, an obelisk partially collapsed, with only three quarters of the structure remaining. A highway which connected Manzanillo with Salagua and Santiago in Colima suffered major damage including large fissures which opened in the

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...

. In

Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...

, the earthquake was felt strongly in the north and western part of the city for at least 40 seconds. It caused mass hysteria and light damage to high-rise buildings.

References

{{Earthquakes in 1973 1973 earthquakes Earthquakes in Mexico 1973 in Mexico 1973 disasters in Mexico 1970s tsunamis

Tectonic setting

Earthquake

Tsunami

Impact

See also

References