After Tuesday’s earthquake in Mexico’s capital, everyone is naturally wondering if such damage and loss of life are avoidable.
And when educated Jaliscienses ask themselves,“Could it happen here?” they sometimes ballyhoo a type of reddish pumice, xal, which is so abundant in JALisco that the state is named after it. Xal often occurs as loose rocks that are said to absorb shock and make the state relatively safe from the deadly shaking of earthquakes. Xal is sometimes used as a landscaping ground cover and can be found laying around everywhere.
But the safety conferred by xal may be a myth, according to some geologists.
“It may be slightly better than a soft, old lakebed, which is what Mexico City is built on,” said Will Prescott, an American geophysicist who has lived and worked in Guadalajara since 2007 and whose specialty during his years with the U.S. Geological Survey was tectonics, earthquakes and volcanoes.
“Those lake sediments amplified the shaking in Mexico City,” he continued. “Xal may not shake as much. But it’s often at the surface so it wouldn’t have much effect.”
“The biggest difference between Guadalajara and Mexico City is there’s a lake under Mexico City—sand and water,” agreed Chris Lloyd, a Canadian geologist who has been living and working just outside Guadalajara since 1994. “When sand and water shake, it looses stability — it liquifies — it sinks.
“Xal is sand, but bigger grains,” Lloyd emphasized. “It doesn’t usually hold water but when it does get full of water, it loses what little strength it has. That’s what happened in Nextipac a few years back. There were tunnels built by the Spaniards that got blocked. They dammed up and then big areas collapsed.
So xal is no anodyne for earthquake worries. Prescott noted that living on “solid rock is best. For example, the eastern part of the United States tends to be solid rock and that causes less shaking.”
Lloyd agreed. “I would say xal is our problem here. It’s not solid. It’s not good to build on. When we get a big one, people will say ‘Why did they let us build here?’”
Some also point hopefully to the fact that Jalisco is not particularly near the Cocos plate, which caused Tuesday’s earthquake. The plate ends at the Pacific coast about where Jalisco begins, so other areas were more affected by its movement.
“Mexico City got a double whammy because of the local geology – the soft sediments – and because it was close to the earthquake,” Prescott said.
But Lloyd pointed out that Guadalajara’s distance from the Cocos plate gives Tapatíos no cause to rest easy. “Yes, the Cocos plate is the really active one and it’s big, so you could say it’s a saving grace we’re not that near it. But Guadalajara is at the junction of three tectonic plates. We have bad earthquakes here. Guadalajara has been flattened three times, the last time around 1932 when half the city was leveled.”
The biggest cause for worry, according to one local geologist who did not wish to be named, is the lack of compliance with building codes throughout Mexico.
“The reason Mexico City buildings fell down is that they didn’t follow building codes. Obras Publicas [Municipal Public Works] are the most corrupt agencies in the country. When you ask for a building permit, they say, ‘Oh, that’s going to take a long time.’ They encourage bribes. And after you bribe them, you expect they’re going to look the other way during inspections.
“There is no reason at all that buildings should have collapsed in Mexico City if everyone had followed building codes. The directors of Obras Publicas should be thrown in jail.”
Lloyd, on the other hand, noted that “building codes in Mexico changed after the terrible earthquake in 1985. You don’t see a lot of old buildings in Guadalajara because past earthquakes leveled them. Hopefully, newer buildings in Guadalajara – the high rises you see going up in the last 10 years – have been done according to code.”
Indeed, during the construction of such buildings, one can observe columns of rebar and cement rising just ahead of the erection of each level. But compliance with anti-earthquake codes is not always optimal.
“I observed one big shopping center as it was built,” said the anonymous local geologist. “It has columns that look very large but inside they put small I-beams, maybe 25 centimeters wide. They should have been about 45. So those huge columns were a sham. You wouldn’t want to be in that shopping center or cinema in an earthquake.”
But Lloyd noted there has been progress in some areas. “There was a big earthquake in Tecomán, Colima, in 1995,” he said. “Then another one in 2003. I drove through two days later and there was no damage because they’d rebuilt well after the ’95 earthquake. It’s a perfect example of how to do things properly.
“Japan gets earthquakes just as bad as here,” he added, “and nothing has collapsed there in 20 years. A Mexican cyclist who went there told me all the Japanese do is run out in the street for a few minutes and then go back inside.”