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How man-made earthquakes work

As it turns out, it’s our fault after all

Earthquakes have become a fairly common phenomenon in recent times. Even if that might not be the case right here in India, United States has seen a significant rise in seismic activity. And no matter what we tell ourselves, there’s an undeniable reason behind all of it – humans. But, wait a minute, human activity causing environmental change isn’t exactly news to us, and neither is that helpful in determining their occurrence or what we can do about it – unless we know exactly what we’re doing wrong. There are numerous studies for several different reasons that are behind induced seismicity, and its about time we knew what they’re all about.

Groundwater injection in oil/gas extraction

According to a 2015 study, between 1973 and 2008, the central part of United States saw an annual average of 24 earthquakes at or above the magnitude of 3.0 on the Richter scale. That number rose to an average of 193 earthquakes a year between 2009 and 2014. That is more than 700% growth in sheer numbers. The same study, by authors Justin Rubinstein of the U.S. Geological Survey (USGS) and Alireza Babaie Mahani of the Geological Survey of Canada, points out that the injection of fluids into the earth is one of the main causes for the rise of seismic activity in the region. Which activities require pushing liquids inside the planet? Quite a lot of industrial processes actually. But a couple of the biggest culprits are oil and natural gas wells, which generate a significant amount of wastewater. Injecting wastewater back into the ground increases subsurface pore pressure, causing faults to slip.

The effects that fluid injection and withdrawal can have on nearby faults can cause
induced seismicity

But we’ve been digging for oil and natural gas for quite a while now, so why the sudden rise? To state it simply, we’re just doing it a lot more – thanks to all new extraction methods. One such method involves going after rock formations that haven’t been previously identified as oil reservoirs, which generates as much as 15 to 50 times the water as compared to oil. As a result, greater quantities of wastewater are being pumped into the earth than ever before. And this isn’t as harmless as it was made out to be for a long time. On September 3, 2016, an earthquake with a magnitude of 5.8 occurred near Pawnee, Oklahoma, followed by nine aftershocks between magnitudes 2.6 and 3.6 within 3 1/2 hours.

Artificial lakes

Another significant factor contributing to man-made earthquakes are large and deep artificial water bodies – like the ones found in dams and reservoirs. In such reservoirs, the weight of the column of water is sufficient to alter the underlying fault or fracture condition by changing the overall stress on the same. It either happens due to an immediate change in the elastic stress of the structure, causing seismicity the first time it is filled, or the water seeps into sub-surface levels and over time, due to decreasing pressure, an earthquake occurs.

The Koyna Dam

One of the most significant earthquakes induced by an artificial water body was right here in India. In 1967, the 6.3 magnitude earthquake in Koynanagar is believed to have been caused by the nearby Koyna Dam reservoir. The epicentre, along with the foreshocks and aftershocks were all located near the dam, although the effect of the quake was felt even 230kms away in Mumbai (then Bombay). One of the most significant earthquake disasters, the 2008 Sichuan earthquake that caused approx 68000 deaths, was also believed to have been caused due to similar seismic activity generated from the nearby Zipingpu Dam.

Enhanced Geothermal Systems

Geothermal energy, or geothermal power, is one of the renewable sources of energy utilised around the world for electricity generation. The way it works is – normal water is passed into the ground, the higher temperature found deep inside the crust heats up that water which is passed back up as steam, which in turn turns a turbine. An improved version of the same process involves pumping pressurised water to enhance permeability, which improves the heating efficiency. This process is known as Enhanced Geothermal System or EGS.

How geothermal energy works

But due to the rock fracturing and shearing that happens, the rock may respond with structural failure. This could and does lead to some very serious seismic activity around EGS sites. Cerro Prieto, Baja California, Mexico saw activity that went up to 6.6 on the Richter scale. Similar instances elsewhere have even led to the cancellation of proposed EGS setups.

Mining

Mining is a human activity that usually involves digging deep and wide into the Earth’s crust. It forms one of the most primary ways of obtaining resources like coal and several metallic ores. But it also leads to another impact – earthquakes. Mines generally operate for a long period of time, sometimes even going as long as 200 years, as was the case with mines in the New South Wales region. A 5.6 magnitude earthquake struck the region in December 1989, causing more economic damage than the value of the coal that was extracted from the mines.

Extensive mining affects tectonic activity, causing earthquakes

One of the most significant reasons behind mining-caused earthquakes is the pumping of groundwater to keep the mines from flooding. Volume-wise, groundwater almost four times the volume of coal is pumped out at the low-end of the mining process. This affects the stress at the underground level, causing tectonic activity leading to earthquakes.

What can we do about it?

If we’re causing all these earthquakes through so many different activities, there has to be something we can do about it, right? Yes, there are some clearly defined ways in which we can avoid the seismic activity caused by human activity, and they are
as follows:

  • Groundwater injection:
    • Setting up monitoring stations
    • Ensuring that such areas are away from high-population zones
    • Not going after oil/gas extraction and moving to renewable sources of energy.
  • Artificial Lakes: Not build dams and reservoirs taller than sustainable.
  • Mining: Reduced-intensity and longevity of mining projects.

The thing is, all this has been known to us for ages – for at least as long as we’ve been causing these earthquakes. But we aren’t really excelling at acting on these measures. But there’s still time, and we sure do hope that the authorities and governing bodies around the world can come to some agreement about man-made earthquakes. After all, it is about the ground under our very feet slipping away.

Arnab Mukherjee

Arnab Mukherjee