|UTC time||1973-01-30 21:01:12|
|Local date||30 January 1973|
|Local time||15:01 CT|
|Duration||2 minutes 40 seconds|
|Depth||35.3 km (21.9 mi)|
|Fault||Middle America Trench|
|Max. intensity||X (Extreme)|
On January 30, 1973, at 15:01 (UTC–6), a magnitude 7.6 earthquake struck 35.3 km (21.9 mi) beneath the Sierra Madre del Sur range in the Mexican states of Colima, Jalisco and Michoacán. On the Mercalli intensity scale, 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.
Off the west coast of Mexico is the Middle America Trench; a convergent plate boundary where the Cocos and Rivera plates subducts beneath the North American Plate at a rate of ~6-9 cm/yr. The interface of this plate boundary is a huge thrust fault known as a megathrust which occasionally produces large megathrust earthquakes and tsunamis.
The January 30 earthquake ruptured a shallow-angle section of the megathrust near a triple junction 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 8 km (5.0 mi) to 43 km (27 mi). It is estimated that a 145 km (90 mi) by 85 km (53 mi) section of the subduction zone was involved in the rupture which propagated at a velocity of 2.7 km (1.7 mi)/s. The rupture occurred on the subduction interface at between 5 km (3.1 mi) and 27 km (17 mi) 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.
The earthquake was powerful enough to be felt across the country to the Gulf of Mexico. 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 and Coahuayana 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.
- ISC (27 June 2022), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 9.1, International Seismological Centre
- ANSS, "Michoacán, Mexico 1973: M 7.5 - 35 km SW of Aguililla, Mexico", Comprehensive Catalog, U.S. Geological Survey, retrieved 5 January 2023
- "Tsunami Event Information S. MEXICO". NGDC. Retrieved 1 January 2021.
- Coffman, Jerry L. (1975). "United States Earthquakes, 1973". US Geological Survey.
- VÍCTOR MANUEL MARTÍNEZ (29 December 2020). "It will be 48 years since the 1973 earthquake in Manzanillo and Colima". El Noticiero en Línea. Retrieved 4 June 2021.
- "10 reported in a quake in Mexico". The New York Times. 31 January 1973. Retrieved 1 January 2021.