The phrase “human-induced seismic hazards” means “man-made earthquakes.” Thanks to oil mining…

Nature has more on the research into the aformentioned artificial earthquakes:

It’s the first thing that geologist Todd Halihan asks on a sunny spring afternoon at Oklahoma State University in Stillwater: “Did you feel the earthquake? My mother-in-law just called to complain that the house was shaking.”

Halihan’s mother-in-law has been calling a lot lately. Fifteen quakes of magnitude 4 or greater struck in 2014 — packing more than a century’s worth of normal seismic activity for the state into a single year. Oklahoma had twice as many earthquakes last year as California — a seismic hotspot — and researchers are racing to understand why before the next major one strikes.

Oklahoma’s quakes have been linked to underground wells where oil and gas operations dispose of waste water, but mining, geothermal energy and other underground explorations have triggered earthquakes from South Africa to Switzerland.

Companies drill into the ground to extract oil and gas mixed with salt water, essentially the brine from a long-fossilized sea. They separate out the fuels and then inject the salt water into deep disposal wells (there are more than 4,600 in Oklahoma).

Much of the liquid ends up in a rock formation called the Arbuckle, which underlies much of Oklahoma and is known for its ability to absorb huge volumes of water. But in many places the Arbuckle rests on brittle, ancient basement rocks, which can fracture along major faults under stress. “The deeper you inject, the more likely it is that the injected brine is going to make its way into a seismogenic fault zone, prone to producing earthquakes,” says Arthur McGarr, who leads research on induced quakes at the US Geological Survey (USGS) in Menlo Park, California.