Tragedy comes in so many ways...............
Mexico has been rocked by its second big earthquake in less than two weeks and could be hit by more.
The magnitude 7.1 earthquake struck central Mexico just after 6pm local time on Tuesday. Its epicentre was located 120 kilometres south-east of Mexico City at a depth of 51km.
Dozens of buildings in Mexico City collapsed and over 200 people are reported dead.
The latest tremor came 11 days after a magnitude 8.1 earthquake occurred off the coast of southern Mexico, killing 98 people.
Both quakes were sparked by heightened tension between the Cocos tectonic plate, which borders the western coast of Mexico, and the North American tectonic plate. As the Cocos plate slid underneath its North American neighbour, it fractured in two different places, known as faults.
“What happened yesterday was most likely a tearing motion in the subducting Cocos plate,” says David Rothery of the Open University in the UK.
The two fractures were several hundred kilometres apart, suggesting the 8 September earthquake did not trigger the 19 September one, says Stephen Hicks at the University of Southampton in the UK. “They were both caused by bending and tension in the Cocos plate, but in different ways. The second earthquake was not an aftershock but a separate quake entirely.”
It is unclear why the two tectonic plates are currently clashing so violently. The depth of the subduction zone – where the Cocos plate is thrusting under the North American plate – makes it difficult to assess how the strain is building up, says Hicks.
The danger is that the two tremors will prompt more, says Hicks. “It’s possible they have increased the stress on nearby faults,” he says. “I also suspect that the magnitude 7.1 earthquake will have its own aftershock sequence, which of course presents a significant hazard.”
According to the US Geological Survey, there have been 19 major earthquakes recorded within a 250km radius of the latest quake. Exactly 32 years ago, on 19 September 1985, a collision between the Cocos and North American plates caused a magnitude 8.0 earthquake that devastated Mexico City and killed 10,000 people.