Understanding the massive March 20 Mexico earthquake

Last update: March 21, 2012 at 11:05 pm by By

Earthquake overview : On 3/20/2012  at about 11:30h local time, a massive earthquake of magnitude 7.4 (Mexican sources are reporting a M 7.8 strength) occurred in the highly populated region of Oaxaca / Guerrero in Mexico. The earthquake’s epicenter was located at  162 km from Oaxaca and 322 km from Mexico City (Distrito Federal).

Read also : our main report of this earthquake : Click here

The March 20, 2012 earthquake occurred as a result of thrust-faulting on or near the plate boundary interface between the Cocos and North America plates. The focal mechanism and depth of the earthquake are consistent with its occurrence on the subduction zone interface between these plates, approximately 100 km northeast of the Middle America Trench, where the Cocos plate begins its descent into the mantle beneath Mexico. In the region of this earthquake, the Cocos plate moves approximately northeastwards at a rate of 60 mm/yr.

Image compiled by Earthquake-Report.com

Historically, there have been several significant earthquakes along the southern coast of Mexico. In 1932, a magnitude 8.4 thrust earthquake struck in the region of Jalisco, several hundred kilometers to the northwest of today’s event.

Seismic Hazard map shows the max. to expect ground acceleration along the coast - image courtesy USGS - Purple line : subduction trench / fault line, green line : transform fault

Magnitude 7 and Greater Earthquakes since 1900 - image courtesy USGS

On October 9, 1995 a magnitude 8.0 earthquake struck in the Colima-Jalisco region, killing at least 49 people and leaving 1,000 homeless.

The deadliest nearby earthquake occurred in the Michoacan region 470 km to the northwest of today’s event, on September 19, 1985. This magnitude 8.0 earthquake killed at least 9,500 people, injured about 30,000, and left 100,000 people homeless.

The 1985 Mexico City earthquake, a magnitude 8.0 earthquake that struck Mexico City on the early morning of 19 September 1985 at around 7:19 am (CST), caused the deaths of at least 10,000 people and serious damage to the greater Mexico City Area. The complete seismic event consisted of four quakes. A pre-event quake of magnitude 5.2 occurred on 28 May 1985. The main and most powerful shock occurred 19 September, followed by two aftershocks: one on 20 September 1985 of magnitude 7.5 and the fourth occurring seven months later on 30 April 1986 of magnitude 7.0. The quakes were located off the Mexican Pacific coast, more than 350 km away, but due to strength of the quake and the fact that Mexico City sits on an old lake-bed, Mexico City suffered major damage. The event caused between three and four billion USD in damage as 412 buildings collapsed and another 3,124 were seriously damaged in the city. While the number is in dispute, the most-often cited number of deaths is an estimated 10,000 people but experts agreed that it could be up to 40,000 (source : Wikipedia)

More recently, a 2003 magnitude 7.6 Colima, Mexico earthquake 640 km to the northwest of today’s event killed 29 people, destroyed more than 2,000 homes and left more than 10,000 homeless.
(text and images : courtesy USGS)

Most important Earthquake Data:
Magnitude :  7.4 (USGS), M 7.8 (Mexico)
UTC Time : Tuesday, March 20, 2012 at 18:02:53 UTC
Local time at epicenter : Tuesday, March 20, 2012 at 12:02:53 PM at epicenter
Depth (Hypocenter) : 10 km
Geo-location(s) :
10 km S Xochistlahuaca (pop 3,566)
20 km E Ometepec (pop 17,801)
165 km SE Chilpancingo (pop 165,250)
193 km (120 miles) E (83°) from Acapulco, Guerrero, Mexico
262 km S Puebla (pop 1,392,099)

Links to important maps
USGS Did You Feel It Map
Google satellite map showing the epicenter and the surrounding area
Historic earthquakes map
Seismic hazard map
Shaking map
Focal mechanism report
Human impact map
GDACS earthquake report

I Have Felt this earthquake

SRC Location UTC Date/time M D INFO
GEOFON Near Coast Of Guerrero, Mexico Mar 20 22:25 4.8 54 MAP I Felt It
EMSC Guerrero, Mexico Mar 20 22:25 5.0 45 MAP I Felt It
USGS Guerrero, Mexico Mar 20 22:25 5.0 21 MAP I Felt It
EMSC Oaxaca, Mexico Mar 20 21:43 4.6 21 MAP I Felt It
USGS Oaxaca, Mexico Mar 20 21:43 4.6 20 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 21:43 4.5 10 MAP I Felt It
EMSC Oaxaca, Mexico Mar 20 20:14 5.1 40 MAP I Felt It
USGS Oaxaca, Mexico Mar 20 20:14 5.1 10 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 20:14 4.9 10 MAP I Felt It
USGS Oaxaca, Mexico Mar 20 19:34 4.8 18 MAP I Felt It
EMSC Oaxaca, Mexico Mar 20 19:34 4.8 10 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 19:34 4.5 10 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 19:19 4.5 10 MAP I Felt It
EMSC Offshore Oaxaca, Mexico Mar 20 19:19 4.7 10 MAP I Felt It
USGS Offshore Oaxaca, Mexico Mar 20 19:19 4.7 13 MAP I Felt It
EMSC Oaxaca, Mexico Mar 20 19:02 5.2 30 MAP I Felt It
USGS Oaxaca, Mexico Mar 20 19:02 5.1 25 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 19:02 5.1 19 MAP I Felt It
EMSC Oaxaca, Mexico Mar 20 18:35 5.0 60 MAP I Felt It
USGS Oaxaca, Mexico Mar 20 18:35 5.1 10 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 18:35 5.0 20 MAP I Felt It
GEOFON Near Coast Of Guerrero, Mexico Mar 20 18:22 5.2 19 MAP I Felt It
USGS Oaxaca, Mexico Mar 20 18:22 5.3 18 MAP I Felt It
EMSC Oaxaca, Mexico Mar 20 18:22 5.3 15 MAP I Felt It
USGS Guerrero, Mexico Mar 20 18:02 7.9 10 MAP I Felt It
  • Acapulco - j'étais au condo au 23 ième étage et j'ai vraiment senti le plancher valsé c'est la première fois que je vis un séisme si fort
  • Jardines del Pedregal, Mexico City - Usually i never feel earthquakes in this part of the city, volcanic rocks on the ground are very stable but this time all my lamps were shaking it lasted about 30 seconds.
  • Distrito federal - Ví las paredes del edificio en el que trabajo agrietándose, apareció un hueco en una de las paredes, el techo tronó, temimos por nuestras vidas realmente. Delegación Cuahutémoc D.F.
  • Tlalpan, Mexico City - I was in south of the city, and suddenly I felt a shaking. I saw many stuffs swing, but the shaking was short.
  • GEOFON Near Coast Of Guerrero, Mexico Mar 20 18:02 7.3 34 MAP I Felt It
  • mexico - Strong shaking indicated
  • Oaxaca de Juarex, MX - I am originally from Washington State so I know what earthquakes can do. Seemed to be more on the moderate shaking scale but not exactly sure, as it has been a while since I experienced an actual shaking earthquake as opposed to a rolling earthquake.
  • acapulco - Strong shaking indicated
  • Toluca,Mexico - Strong shaking indicated
  • Mexico DF - as usual isn't an nice experince
  • Copilco, DF, Mexico - Moderate shaking indicated
  • Mexico City - 3rd floor of some sturdy 5-floor buildings that survived the last big one. I often don't even notice weaker quakes, but this one had very noticeable shaking, which even made me dizzy, and lasted 20-30 seconds.
  • Mexico - Moderate shaking indicated
  • Puerto Escondido, Oaxaca - Got me running out of the house! still felt the dirt in street moving under me for several minutes.
  • Mexico City, Mexico - I could feel the ground shaking and see the walls moving for at least a minute. It was more severe than the earthquake on December 11, 2011. We almost immediately lost power as well.
  • Puebla - Strong shaking indicated
  • Mexico DF - I Have witnessed the earthquake that occured back in december. This was much more strong than before. It started out as a little one but the longer it went on it got stronger. It honestly felt like my eyes were going cross-eyed i couldnt even see straight the whole house was moving. Scary things to deal with!!!
  • Mexico City - It was a side-to-side type shaking/waving, and definitely the strongest I've felt. I was on the 5th floor and felt it was necessary to leave the building. Many of the residents did the same, running down the stairs and waiting outside until it let up.
  • Hidalgo - Strong shaking
  • Cuernavaca, Mexico - The rolling got me to run out of my house with my daughter. Moderate shaking of my ceiling fans. Also, felt an aftershock about 10 minutes later. Can not get a hold of my husband who is in Mexico City. The phone lines are down.
  • Mexico City - I am native from Mexico City. This earthquake felt very strong and with long duration. I live in the north part of the city. It seems there are no critical events, right now people is calm and everything is continuing as always.
  • Cuernavaca, Morelos - about 30 seconds
  • MEXICO - I am out in Atizapan de Zaragoza in the hills and I never feel earthquakes but this one I did. The hanging light pendants were swinging and the house was shaking, I almost thought the house was going to fall. I have never felt anything like it.
  • Oaxaca - Was having a coffee with friends when it all started. Hope that was all...
  • Puerto Escondido, Oaxaca - It felt really strong here, because it was an oscillatory movement and we are about 300km from the epicenter, thankfully no reports of people injured or constructions damaged so far (14:13 EST)
  • Nuevo Vallarta - I WORK IN A RESORT MY BUILDING IS ONLY 9 FLOORS HIGH, I´M USUALLY WORKING AT THE SECOND FLOOR BUT TODAY I WAS AT THE EIGHT FLOOR EXACTLY WHEN IT HIT AND OMG I GOT SCARED WOW IT WAS STRONG ... WE HAVE LOT OF POOLS AND FROM THE BIG WINDOW WE HAVE IN OUR FLOORS I SAW HOW THE WATER FROM THE POOLS WAS MOVING WOW MY FIRST EARTHQUAKE HERE IN MEXICO....
  • Chilpancingo, GRO - Still moving!
  • Mexico - While shopping at Sam's, we felt marked tremors. Cashier told us to leave, could not help but notice how calm and polite everyone was. Staff very courteous, shoppers left calmly and did not cause any pandemonium. Very professional and impressive. Earthquake a little scary but not dramatic. Light fixtures moved ceiling moved, sirens blasting
  • México, D.F. - Me pareció similar al de 1985. Vivo en una zona al sur de la Ciudad de México donde el suelo volcánico debió de amortiguar el temblor. Pero no fue así.
  • Mexico City - It began softly and in a jerk got stronger, building was making strong noises but nothing to worry to much, people was calm in general and all went good in the business center of the city (Santa Fe) lot's of people in the streets after initial shock slowly going back to work ;)
  • Puerto Escondido, Oaxaca - I was in a small grocery store when a whiplash type motion hit, things swayed, some stuff was thrown off the shelves onto the floor. It was all over in a few seconds. Several of us crowded into the small doorway for 30-40 seconds before moving on. Went home, checked the house and found no damage. Looked for the possibility of a sea surge, but nothing happened, so I went to the beach about 3PM. Guerrero is hilly and very close, about 100 miles north. Have never heard about volcanic activity ther
  • Puerto Escondido, Oaxaca - I was in a small grocery store when a whiplash type motion hit, things swayed, some stuff was thrown off the shelves onto the floor. It was all over in a few seconds. Several of us crowded into the small doorway for 30-40 seconds before moving on. Went home, checked the house and found no damage. Looked for the possibility of a sea surge, but nothing happened, so I went to the beach about 3PM. Guerrero is hilly and very close, about 100 miles north. Have never heard about volcanic activity ther
  • Mexico City - Estoy al sur de la ciudad por el Estadio Azteca,se sintio fuerte pero todo en orden
  • México City - Movimiento rápido de norte a sur y luego de este a oeste, imposible caminar, activación de alerta sísmica, perdida de energia, no comunicaciones, desplazamiento de 50 centimetros de las lámparas. Me recordo a terremoto 1985.
  • Tlatelolco, Mexico City. - Vivo en el piso 23 de una torre habitacional. El sismo empezó cmo otros pero tomo fuerza. Me preocupé cuando libros y otros objetos empezaron a volar alegremente. La fuerza del sismo era tal que era imposible ponerse de pie/I live on the 24th floor of a bulding in this area. The quake began slowly but began to be stronger and stronger, books and objets from shleves began to fly around. It was so intense that it was impossible to stand up. A frightening experience!
  • Mexico City - I'm located in the Del Valle neighborhood in Mexico City. Firstly, Mexico City's Seismic Alert System went off, some 50 seconds prior to the first seismic waves hitting the building. At the beginning, the rolling movements were gentle, but after 30 seconds the ground shaking became nerves-breaking. The strong part of the earthquake lasted nearly 30 seconds, and then it went down to an almost imperceptible rolling movement that lasted almost 3.5 minutes, due to muddy soil conditions underneath.
  • EMSC Guerrero, Mexico Mar 20 18:02 7.4 19 MAP I Felt It
    USGS Oaxaca, Mexico Mar 20 18:02 7.4 20 MAP I Felt It

    SHARE YOUR EARTHQUAKE EXPERIENCE WITH US

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    Country where you felt the earthquake
    City/Village where you felt the earthquake
    Street or suburb (area) where you felt the earthquake
    MMI II (Very weak shaking) ?
    People :
    Felt by persons at rest, on upper floors or favorably placed.
    MMI III (Weak shaking) ?
    People :
    Felt indoors; hanging objects may swing, vibration similar to passing of light trucks, duration may be estimated, may not be recognized as an earthquake.
    MMI IV (Light shaking) ?
    People :
    Generally noticed indoors but not outside. Light sleepers may be awakened. Vibration may be likened to the passing of heavy traffic, or to the jolt of a heavy object falling or striking the building.
    Fittings :
    Doors and windows rattle. Glassware and crockery rattle. Liquids in open vessels may be slightly disturbed. Standing motorcars may rock.
    Structures :
    Walls and frames of buildings, and partitions and suspended ceilings in commercial buildings, may be heard to creak.
    MMI V (Moderate shaking) ?
    People :
    Generally felt outside, and by almost everyone indoors. Most sleepers awakened. A few people alarmed.
    Fittings :
    Small unstable objects are displaced or upset. Some glassware and crockery may be broken. Hanging pictures knock against the wall. Open doors may swing. Cupboard doors secured by magnetic catches may open. Pendulum clocks stop, start, or change rate.
    Structures :
    Some large display windows cracked. A few earthenware toilet fixtures cracked.
    MMI VI (Strong shaking) ?
    People Felt by all. People and animals alarmed. Many run outside. Difficulty experienced in walking steadily.
    Fittings :
    Objects fall from shelves. Pictures fall from walls. Some furniture moved on smooth floors, some unsecured free-standing fireplaces moved. Glassware and crockery broken. Very unstable furniture overturned. Small church and school bells ring. Appliances move on bench or table tops. Filing cabinets or "easy glide" drawers may open (or shut).
    Structures :
    Slight damage to buildings with low standard. Some stucco or cement plaster falls. Large display windows broken. Damage to a few weak domestic chimneys, some may fall.
    Environment :
    Trees and bushes shake, or are heard to rustle. Loose material may be dislodged from sloping ground, e.g. existing slides, talus slopes, shingle slides.
    MMI VII (Very strong shaking) ?
    People
    General alarm. Difficulty experienced in standing. Noticed by motorcar drivers who may stop.
    Fittings :
    Large bells ring. Furniture moves on smooth floors, may move on carpeted floors. Substantial damage to fragile contents of buildings.
    Structures :
    Unreinforced stone and brick walls cracked. Low standard buildings cracked with some minor masonry falls. A few instances of damage to buildings of ordinary workmanship. Unbraced parapets, unbraced brick gables, and architectural ornaments fall. Roofing tiles, especially ridge tiles may be dislodged. Many unreinforced domestic chimneys damaged, often falling from roof-line. Water tanks Type I burst. A few instances of damage to brick veneers and plaster or cement-based linings. Unrestrained water cylinders (hot-water cylinders) may move and leak. Some common windows cracked. Suspended ceilings damaged.
    Environment :
    Water made turbid by stirred up mud. Small slides such as falls of sand and gravel banks, and small rock-falls from steep slopes and cuttings. Instances of settlement of unconsolidated or wet, or weak soils. Some fine cracks appear in sloping ground. A few instances of liquefaction (i.e. small water and sand ejections).
    MMI VIII (Severe shaking) ?
    People Alarm may approach panic. Steering of motorcars greatly affected. Structures : Low standard buildings heavily damaged, some collapse. ordinary workmanship buildings damaged, some with partial collapse. Reinforced masonry or concrete buildings damaged in some cases. A few instances of damage to buildings and bridges designed and built to resist earthquakes. Monuments and pre-1976 elevated tanks and factory stacks twisted or brought down. Some pre-1965 infill masonry panels damaged. A few post-1980 brick veneers damaged. Decayed timber piles of houses damaged. Houses not secured to foundations may move. Most unreinforced domestic chimneys damaged, some below roof-line, many brought down. Environment : Cracks appear on steep slopes and in wet ground. Small to moderate slides in roadside cuttings and unsupported excavations. Small water and sand ejections and localized lateral spreading adjacent to streams, canals, lakes, etc.
    MMI IX (Violent shaking) ?
    Structures Many low standard buildings destroyed. Ordinary workmanship buildings heavily damaged, some collapse. Reinforced masonry or concrete buildings damaged, some with partial collapse. Buildings and bridges designed and built to resist earthquakes damaged in some cases, some with flexible frames seriously damaged. Damage or permanent distortion to some buildings and bridges, designed and built to normal use standards. Houses not secured to foundations shifted off. Brick veneers fall and expose frames. Environment : Cracking of ground conspicuous. Landsliding general on steep slopes. Liquefaction effects intensified and more widespread, with large lateral spreading and flow sliding adjacent to streams, canals, lakes, etc.
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