Sunday's 7.2 Mexicali earthquake was the third major quake to rattle the western hemisphere in less than three months.
The quake was more powerful than the 7.0 earthquake that left more than 200,000 dead and more than 1 million homeless in Haiti on Jan.12. It was also a relatively shallow earthquake, at six miles underground, meaning there was less earth to absorb the shaking.
But with only two reported dead, the damage is far more contained than the quake that destroyed Haiti’s capital, Port-au-Prince, and the massive 8.8-magnitude quake that left 700 dead in Chile on Feb. 27.
One reason for the lower death toll and damage is that the epicenter of Sunday’s quake was in an agricultural belt with few buildings 38 miles from the city of Mexicali in northern Mexico. The Haiti quake was only 18 miles from its densely populated capital of 2.5 million people.
“The secondary factor would be seismic codes,” says Eduardo Miranda, a civil engineer specialized in earthquakes at Stanford University, who has studied earthquakes in the Mexicali region and is heading there this week. “Both in Mexico and the US we have seismic codes that in general are being enforced. There is a culture of earthquakes.”
Felt by 20 million people
Final reports are not in, with communications down and reports of residents still trapped in rubble. But an earthquake that could have wrought enormous damage appears to have killed few and injured about 100 people, mostly by objects falling from shelves and counters in Mexicali.
Still, residents remained shaken Monday, especially with constant aftershocks.
“It is nothing like the damage in Haiti or Chile,” says Gabriela Marquez, who works in communications for the government tourism office in Mexicali. She says most hotels sustained limited damage and once again have water and electricity. “Mostly it is just fear, each time there is an aftershock.”
But geography alone did not help limit damage. Just as in Chile, where a massive 8.8-magnitude quake, one of the strongest in a century, killed far fewer people than in Haiti, building codes and enforcement of them here most likely played a critical role, too.
Strict building codes
Mexico has decades of experience with earthquakes. One of the region’s most infamous devastated Mexico City in 1985.
Sergio Alcocer, the secretary general of Mexico's National Autonomous University and an engineer, says that strict codes exist in Mexicali, not just because of Mexico's history of earthquakes but also because of its proximity to the US.
"They have been influenced by American engineering," he says.
Experts from both countries share research and therefore end up with similar building codes, says Stephen Mahin, a structural engineer at the University of California, Berkeley. He says that Mexicali's proximity with the US has led to a robust interchange of information on how to build correctly.
Mr. Miranda says that, unlike in the US, residential housing does not have the same standards as commercial buildings, which means many people build their own homes without the input of an engineer. But he says people still build smarter because of their experience with earthquakes.
Just across the border from Mexicali, the US city of Calexico's fire chief Peter Mercado says there was significant structural damage to the downtown area, but he also praises the rigorous enforcement of strict building code for the limited damage. “No buildings are completely on the ground,” he says. “We are talking about walls fallen, bricks fallen, cracks on buildings.”
Timing also a factor
There were no reported deaths on the US side of the border. Mr. Mercado also says the timing – on Easter Sunday when most weren’t out shopping or at offices – may have contained damage as well.
Regardless of its widespread impact, a 7.2-magnitude earthquake is not terribly rare.
The USGS says according to averages recorded since about 1900 the world should expect approximately 18 major earthquakes, between 7.0 and 7.9, every year. In fact, the question is not why damage was so limited in Mexicali but why it was so widespread in Haiti.
“The more constructive way to look at it highlights the fact that Haiti, being such a poor country, has no money to adhere to building codes,” says Mr. Blakeman.