Tornado Alley to Earthquake Valley

Tornado Alley to Earthquake Valley

In this Sept. 20, 2017 file photo, volunteers and rescue workers search for children trapped inside the Enrique Rebsamen school, collapsed by a 7.1 earthquake in southern Mexico City. Mexico’s Education Department says authorities have revoked the permits of the elementary and middle school that collapsed in the devastating, killing 26 people. (AP Photo/Miguel Tovar, File)

Earthquakes have shaken communities around the globe in recent weeks, resulting in collapsed buildings, panicked locals and hundreds of deaths.  Mexico, Asia and several Pacific islands have seen earthquakes over 6.0 magnitude in the past 30 days alone.

An 8.1 magnitude earthquake hit Mexico on Sept. 8, killing more than 90 people.  The epicenter was about 600 miles off the southern coast in the Pacific Ocean, but felt as far away as Mexico City and Guatemala City.  The temblor was the largest experienced in a century in Mexico, barely taking the record from a magnitude 8.0 earthquake in September 1985.

Twelve days later, on Sept. 19, a 7.1 magnitude earthquake struck, killing over 300 people.  The epicenter was near Puebla in central Mexico, about 75 miles from Mexico City.  This temblor came just hours after commemorative events for the anniversary of the 1985 Mexico City earthquake that killed thousands and injured around 30,000.

Damage from both earthquakes are estimated to cost around $2 billion.

“A smaller quake closer to more people can do more damage,” tweeted Lucy Jones, a Southern California seismologist and U.S. Geological Survey scientist emerita.  The second was smaller in magnitude, but closer to a larger population of people and structures.

Oklahoma has experienced frequent earthquakes in recent years, but none over 6.0 magnitude.  The largest was a 5.8 magnitude quake near Pawnee on Sept. 3, 2016.  From 2014-2016, Oklahoma had 2,098 quakes, compared to the meager 212 from 2011-2013.

The difference between Oklahoma’s frequent small earthquakes and Mexico or Asia’s infrequent large quakes is tectonic plates.  Mexico is in a subduction zone, an area where part of the crust is sliding slowly under another part and causing friction and pent-up energy.  The continental North American Plate is going over the sinking Cocos Plate, creating a high friction subduction zone.

Subduction zones are responsible for many of the world’s strongest earthquakes.  Quakes of 9.0 magnitude and higher can only occur in subduction zones, according to Gavin Hayes, a research geophysicist with the U.S. Geological survey, as quoted in the New York Times.  Japan, Indonesia, Alaska and Chile have recorded quakes over magnitude 9.0 and all are in powerful subduction zones that create “megathrust” earthquakes.  Had Mexico’s earthquakes happened on the boundary of the plates, not on either one, the quakes would have been megathrusts.

Dr. Hayes told the New York Times that Oklahoma’s earthquakes have been “human-induced,” as a result of wastewater injection.   Sooner Lake Fault is a new fault that was recently discovered by a team from NASA’s Jet Propulsion Laboratory.  The team found the fault to be the location of multiple earthquakes, but the signs in the makeup of the fault are consistent with human-induced, not natural quakes.

“It’s more about the disposal of the water from the fracking than it is about the actual fracking.  By doing that, they usually pump that water down wells,” said Perry Pogue, chief geologist for Total Exploration & Production.  “If those wells happen to intersect one of these deeper, smaller faults, they can basically cause (sic) a release of that fault by pumping the water in there and create a small earthquake.”

Wastewater, containing metals and toxins, generally comes from oil and gas operations.  The water could be harmful to normal groundwater, leading companies to inject it deep underground to avoid contamination.  Injections into old, quiet faults can bring back activity and cause earthquakes as a result.

 

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