As September's duo of deadly earthquakes made so painfully clear, Mexico is a highly seismic country. Sadly, there's no accounting for the dangers of plate tectonics. But could human activity also be contributing to Mexico's propensity for earth-shaking events? Quite possibly, according to the Mexico City-based newspaper El Universal, which reports that oil exploration in the northern state of Nuevo León has led to stronger and more frequent earthquakes over the past decade.

Hydraulic fracturing, or "fracking," is a drilling technique used to exploit oil trapped in shale stone. Research by the Autonomous University of Nuevo León suggests that fracking in the state caused 304 earthquakes from 2006 to 2016. While most were relatively weak, a 4.5 magnitude earthquake in November 2013 caused damage in several towns.

The first wells were drilled in 2006 in the Agua Nueva and Pimienta rock formations. Since then, the years with the highest numbers of new wells also recorded the highest numbers of earthquakes. "We found a direct relationship between fracking and the earthquakes reported since 2006," UANL department head Dr. Juan Manuel Rodríguez Martinez told El Universal.

The federal government recently approved new fracking guidelines for oil companies and expanded the areas where they could drill for oil. The new guidelines could allow fracking in blocks just 30 km from the state capital of Monterrey, home to more than 4 million people.

Beyond the temblors caused by fracking, the practice could also contaminate the water supply in the state's most populous areas. Fracking requires millions of liters of water to be mixed with chemicals and pumped into the ground, and researchers are concerned that the process will pollute local rivers without adequate treatment. "More than 60% of the state is now open to fracking," said UANL biology researcher Antonio Hernández Ramírez. "There is a real possibility that our water could be affected."

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