Earthquake in Colima, Mexico AE 538 January 30, 2003

Home , Colima City

Michelle Mentzer

Seismology Aspects

At 2:06:35 (UTC) on Wednesday, January 22, 2003, a major earthquake occurred

near Colima, Mexico. This was the largest earthquake in the area since October of 1995,

when a magnitude 8.0 earthquake occurred. According to the U.S. Geological Survey,

this earthquake registered a magnitude of 7.8. Mexico’s national seismological service

measured it at a magnitude of 7.6. The earthquake lasted for approximately 45 seconds

and caused a large amount of damage to central Mexico. At least 29 people were killed

in this event and 300 were injured.

The epicenter of the earthquake occurred in a seismically and volcanically active

region, close to the juncture of three tectonic plates. This juncture is located just off the

coast of central Mexico. To the north-east is the North American Plate, the Rivera Plate

is to the north-west, and the Cocos Plate is to the south. The Rivera Plate and the Cocos

Plate have been moving beneath the North American plate at different rates. The Rivera plate is moving north-west at around 2 cm per year, whereas the Cocos plate is moving the same direction at a rate of about 4.5 cm per year. This area is in a shallow region, which makes it particularly dangerous. The damaging effects of an earthquake depend on its depth and the kind of soil through which it passes. For instance, Mexico City is at a particularly high risk due to the soil beneath it. The soil below is actually the silt of an old river bed, which amplifies the vibrations. Had the surrounding area been inhabited, this could have been a much worse disaster. However, while the depth of this earthquake Michelle Mentzer

was a relatively shallow 20.5 miles, the fact that the epicenter was in an uninhabited area greatly reduced the damaged it caused.

A series of aftershocks ranging from a magnitude of 3.9 to 5.8 followed the initial quake. The 5.8 magnitude aftershock occurred Wednesday afternoon and was strong enough to chase people out of their homes. Despite the scare, none of these aftershocks did significant additional damage.

Area Affected

The earthquake occurred about 310 miles west of Mexico City. Effects were felt throughout a large part of southwestern Mexico. The majority of fatalities, injuries and

damage occurred in Colima, with some additional

injuries and one death in southeastern Jalisco. A

state of emergency was declared in six Colima

towns including Colima City, Armeria,

Coquimatlan, Ixtlahuacan, Villa de Alvarez, and

Tecoman. Effects of the earthquake were also felt in Guadalajara, over 100 miles away from the epicenter. Mexico City residents also felt strong effects of the earthquake, but the city suffered little damage. It is feared that more

damage and fatalities could have occurred in regions that are difficult to reach due to

their isolation in the mountains.

Types of Damage of Built Environment

The earthquake caused damage to many buildings such as homes, hospitals, banks, and offices. It also ruined the road infrastructure created power outages and gas

leakages. The area affected by the earthquake was heavily populated by adobe houses Michelle Mentzer that were built between 50 and 100 years ago. These houses crumbled and were completely demolished in the earthquake, leaving many residents homeless. At least 166 homes were ruined in Colima City alone.

Residents of Tecoman chose to sleep in tents outside after the initial quake caused large cracks in their houses. They feared that these cracks may have left their homes structurally unstable. Villa de Alvarez in the state of Colima suffered the worst with 10 % of homes suffering some sort of damage. Preliminary reports said that a total of around 8,820 houses suffered earthquake related damage in the state of Colima. Of these homes, 2,005 were completely destroyed, while the damage on the rest ranged from severe to minor. Office buildings also collapsed in Colima City and people were left trapped inside of many of the collapsed structures. Historical buildings dating back to 1522 were lost in the city’s core. In

Guadalajara, bells fell from an ancient church tower and many homes partially collapsed.

Less severe effects were felt in Mexico City where power lines fell and people quickly evacuated buildings as they shook.

Causes of Damage The majority of the damage was caused by the vibrations originating at the hypocenter of the earthquake and traveling through the earth to the surrounding areas.

The small adobe houses in these areas had been there for as long as 100 years and were not designed to withstand the kinds of forces that were imposed by this earthquake. They could not hold up in the vibrations, and they crumbled completely. Michelle Mentzer

Some of additional damages were indirectly caused by the earthquake. Additional damage occurred in Mexico City when adjacent 20 story buildings swayed enough to bump into one another. However, this was not the cause of the most severe structural damage. Engineers who surveyed Mexico City reported little significant structural damage. The vibrations also caused landslides which did some damage of their own. A landslide was responsible for closing a section of the Colima-Guadalajara highway. Michelle Mentzer

References

USGS Webpage: http://neic.usgs.gov/neis/bulletin/neic_phac.html

“Thousands of Mexicans homeless after earthquake” Newsobserver.com:

http://newsobserver.com/24hour/world/story/732003p-5341322c.html

“Deadly Quake” ABCNews.com:

http://www.abcnews.go.com/sections/world/DailyNews/mexico030122_quake.ht

“At least 25 killed in Mexican Quake” MSNBC News:

http://www.msnbc.com/news/862555.asp

“Mexican quake death toll rises to 29” CNN.com:

http://www.cnn.com/2003/WORLD/americas/01/23/mexico.earthquake/index.htm

“Powerful quake hits Mexico” BBC News:

http://news.bbc.co.uk/2/hi/americas/2682303.stm

“Mexico tallies quake casualties Death toll hits 29 as country digs out from 7.8 temblor”

SFGate.com: http://www.sfgate.com/cgi-

bin/article.cgi?f=/chronicle/a/2003/01/23/MN138867.DTL

Mexicans dig for survivors of monster earthquake” The Salt Lake Tribune:

http://www.sltrib.com/2003/Jan/01232003/nation_w/22611.asp