How Earthquakes Can Be Triggered By People

Earthquakes are typically thought to be an utterly uncontrollable natural disaster. Seemingly, there's no way that humans could have any control over the massive tectonic plates beneath their feet, so the only thing to do in terms of earthquake prevention is focus on being prepared and having solid infrastructure. But in fact, many earthquakes in recent history have been induced by human activity.

The impact of human-induced earthquakes has been so strong that in the United States, Oklahoma City is at a higher risk of seismic activity than California. And human-induced earthquakes aren't always accidental. Weapons like the earthquake bomb are specifically designed to send shockwaves similar to those set off by an earthquake. Meanwhile, tectonic weapons have also been theorized as a way to trigger earthquakes as a means of warfare. And while some induced seismic activity has decreased as mining activity has decreased, an increase in fracking has been found to be directly correlated with a rise in seismic activity.

But the devastation wrought by earthquakes is not entirely uncontrollable, regardless of whether or not they're induced accidentally or on purpose. Ultimately, most people can agree that less earthquakes is always the best number of earthquakes. These are some of the ways earthquakes can be triggered by people.

Mining projects are another frequent cause of human-induced earthquakes. This tends to occur because when large amounts of rock and earth are moved during mining, this causes stress changes in the surrounding rock mass along with the creation of faults and fracture planes. Roughly 37% of all human-induced earthquakes are caused by mining activity, with coal mining being the largest culprit. In places like the United Kingdom, as coal production has decreased, so has the number of human-induced earthquakes, according to Marine and Petroleum Geology.

In Newcastle, New South Wales, Australia, the emergence of a mining industry in 1801 resulted in an increase of seismic activity in the region throughout the 19th and 20th centuries. In 2014, the largest mining-related earthquake in South Africa was recorded with a magnitude of 5.5 and stemmed from a gold-mining area– one 31-year-old man died as a result. And in Germany, salt mining has resulted in earthquakes with magnitudes as high as 5.6. Sometimes, mining can even cause thousands of small earthquakes throughout the year, as is the case in the Legnica-Glógow Copper District in Polkowice County, Poland, writes Frontiers in Earth Science. Generally, tunnel collapses during mining are most often responsible for induced earthquakes.

And the act of mining itself isn't the only thing that can cause an earthquake. On August 6, 2007, a coal mine collapse in the Crandall Canyon Mine in Utah, United States, triggered a magnitude 3.9 earthquake.

Fracking isn't the only kind of oil and natural gas extraction method that causes earthquakes. Even conventional oil drilling and natural gas extraction has been known to cause earthquakes for years. The rise in seismic activity in Los Angeles, California, between the 1920s and 1940s is even attributed to oil drilling in the area, although it's believed that rather than directly causing the earthquakes, oil drilling made them happen sooner than they necessarily would have. The 1933 Long Beach earthquake is one of many earthquakes at this time associated with oil drilling.

Waterflooding, a technique used in oil production that involves injecting water into a reservoir, has also been shown to cause earthquakes. After an oil field in Snyder, Texas, was waterflooded between 1957 and 1982, a series of earthquakes were recorded up through 1982. A 2013 study published in PNAS also suggested that carbon dioxide injection, which is also used in oil production, may have contributed to the rise in seismic activity in Texas.

Some oil wells operate in and make wastewater injections into shallower levels of rock in an attempt to decrease the chance of earthquakes. But according to Science, this actually causes more frequent and stronger earthquakes than deeper injections. Shallow injections have been found to cause earthquakes with magnitudes up to 4.7, while deeper wastewater injections caused smaller earthquakes at magnitude 2.0.

Over the past few decades, carbon capture and storage (CCS) have become a popular method to try to bypass carbon emissions. But one method of CCS — pumping fluid carbon dioxide underground into porous rocks — has been found to cause earthquakes up to magnitude 3 or more. Some of the 100 earthquakes in West Texas between 2009 and 2010 were found to be caused by CCS, and it has been suggested that CCS caused the 2018 Hokkaido Eastern Iburi earthquake in Japan, but this is debated among researchers.

Unfortunately, there is little consistency with which CCS causes earthquakes, and it's been found to happen in some places more than others. And because earthquakes of any size can cause the carbon dioxide to be released, more viable methods of CCS might need to be considered. But according to MIT Climate Portal, it's possible to mitigate the risk of earthquakes associated with CCS by only injecting carbon dioxide into soft sedimentary rock that isn't near a fault line. In 2013, Yale researchers also suggested that storing carbon dioxide in chemically reactive mafic rock could help avoid causing earthquakes. 

In 1961, the United States Army started disposing of toxic wastewater from napalm production by injecting it into a well drilled into the Rocky Mountains. The wastewater came from a chemical weapons manufacturing plant near Denver, Colorado, known as the Rocky Mountain Arsenal and over the course of five years, up to 165 million gallons of wastewater was injected into the Rocky Mountains.

During this time, over 1,500 earthquakes were recorded in the region, with a drastic increase in frequency, and almost all of the earthquakes occurred within 5 miles of the well where the toxic wastewater was being injected. The strongest earthquake recorded had a magnitude of 5.3 and occurred a year after wastewater injections ceased.

Due to the fact that this wastewater disposal was causing earthquakes, the Army abandoned the well in February 1966, and permanently sealed it in 1985. But despite abandoning the well, earthquakes continued in the region until 1981. And according to a bulletin from the U.S. Geological Survey, the fact that the strongest earthquake occurred after use of the well was abandoned demonstrates how uncontrollable earthquakes caused by wastewater injections may be.

In September 2015, the Sea of Galilee experienced a series of earthquakes that lasted four days, caused by Israelis pumping fresh water from underground aquifers. Another series of over a dozen earthquakes in July 2018 was also attributed to groundwater extraction. North of Delhi, India, a region known as the Aravalli-Delhi Fold Belt has also seen an increase in seismic activity caused by groundwater pumping.

In 2011, the region of Murcia experienced one of its worst earthquakes in over half a century near Lorca, Spain, when a magnitude 5.1 earthquake caused the deaths of nine people. The earthquake was caused by slippage near a water basin, and groundwater extraction was responsible for the extensive damage that the earthquake caused.

It's been suggested that groundwater extraction in California may also be affecting the San Andreas Fault. The pumping of groundwater in California is largely for irrigation purposes and has been depleting the groundwater since the mid-1800s. The amount of small earthquakes especially has increased as a result, with the amount doubling every year between 1984 and 2005. While the San Andreas fault will always be a center for seismic activity, groundwater extraction may be stressing the fault more often than ever.