HUMAN ENGINEERED EARTHQUAKES

Dr. Hrishikesh Baruah

Asst. Professor (Sr.), Department of Geology, Arya Vidyapeeth College,

Guwahati: 781 016

hbaruah@hotmail.com ; +919864030992

For a common man, earthquake is a manifestation of nature’s discontent. Many people may never comprehend the fact that human beings have acquired the capability to produce earthquakes long back. So, when an earthquake occurs, very few would ever even bother to think, "Was that natural or man-made?” In fact, human activities can trigger earthquakes unwittingly or calculatedly in the most undesired places.

Human-caused quakes are mostly tiny, registering less than four on geologist’s seismic scales and they don’t occur along natural faults but can be attributed to mining tons of say, coal leading to mine’s roof collapses. However, some human actions can trigger much larger quakes along natural fault lines simply because anthropogenic activities can toss enough mass around to shift the pattern of stresses in the Earth’s crust. Faults those were hitherto dormant for a million years can suddenly be pushed to failure.

What are the ways by which anthroquakes can be triggered?

Big dams that retain huge quantities of water can generate earthquakes by what can be called "hydro-fracturing," in which weight of the water stresses fractures in the underlying rock. A leading scholar on the topic, H. K. Gupta (2002) in his review of studies on Reservoir Triggered Seismicity (RTS) highlights that globally, there are over 90 identified sites of earthquakes triggered by the filling of water reservoirs. In fact, the largest and most damaging earthquake (M = 6.3) triggered by a man-made reservoir occurred in 1967 in Koyna, India. India experienced two more such quakes due to failures in 1983 at Bhatsa in Maharashtra (M = 4.9) and 1993 at Killari or ‘Latur’ in SW India (M = 6.1). China has had a number of RTS incidents. In fact scientists say it is possible that the 320 millions of tons of water in the Zipingpu Dam played a direct role in the devastating earthquake in Sichuan, China in May 2008. Christian Klose (2008), a geophysical hazards research scientist from Columbia University explained using geophysical data, how it likely happened. RTS trends show that the magnitude of the foreshock is higher than the magnitude of the aftershock and, both values are generally higher than in cases of natural earthquakes. Latest moves to tap the hydroelectric potential of north east India may increase the probability of RTS as this region is one of the most tectonically active places in the whole world.

Waste disposal, particularly if it is toxic has been a headache for the civic planners. In early 1960s, Denver, a relatively earthquake free city experienced an uncharacteristic series of tremors. Geologist, David Evans traced the cause to a 4000 metres deep sewage disposal well which penetrated a fault zone in the Rocky Mountains.

Globally 75% of extracted coal is used for electricity production. In case of India, it is 67%. Such a situation demands that a lot of coal mines work overtime. To meet the demands, miners pulled 6,195 million metric tons of coal out of the Earth in 2006 alone. Often water needs to be pumped out along with the coal, sometimes extracting dozens of times as much water as coal. This leads to a lot of mass transfer that can modify the prevailing stress-strain regime in an area thereby leading to a quake. The greatest earthquake in Australia's history that reached 5.6 in magnitude struck Newcastle in New South Wales on December 28, 1989, killing 13 people, injuring 160, and provoking damages estimated to 3.5 billion U.S. dollars. Tectonic changes, due to 200 years of underground coal mining, were the trigger.

Three of the biggest anthroquakes (M ranging between 6.9 and 7.3) of all time occurred in Uzbekistan's Gazli natural gas field between 1976 and 1984. The combination of liquid extraction and injection changed the tectonic system in the field. A similar situation also occurred in the late 1960s in an oilfield near Rangely in Colorado.

Way back in 2005, a geologist claimed that the world’s then-tallest building, the Taipei 101 weighing more than 700,000 metric tons, was stimulating earthquakes in a long-dormant fault in Taiwan. Although it isn’t outside the realm of possibility for a building to create an earthquake, more studies are necessary to be done.

Tectonic warfare has been a less known and classified field of research and activities definitely having its roots in the concepts of telegeodynamics as developed by the visionary scientist Nikola Tesla. While celebrating his 79^th birthday in 1935, Tesla shared with reporters the concepts of what he described as "controlled earthquakes." After his death in 1943, the US Government confiscated all of his papers, and the FBI declared them classified until further notice.

Nuclear explosions also cause earthquakes that are felt as shaking and recorded by seismographs all around the world. But not even the largest bomb test has ever induced a natural earthquake.

Climate and carbon are set to influence one and all in the coming future. That global warming can influence earthquakes was one of the conclusions of the researchers who got together at the conference on ‘Climate Forcing of Geological and Geomorphological Hazards’ in London on September 2009. That a link between climate and the rumblings of the crust exists has been around for years, but only now is it becoming clear just how sensitive rock can be to the air, ice and water above.

Subtle changes in sea level do influence under water seismicity. Researchers have found a distinct relationship between El Nino and quakes on the Easter micro plate - the tectonic plate that lies beneath the ocean off the coast of Easter Island. Since 1973, the arrival of El Nino every few years has correlated with a greater frequency of underwater. El Nino raises the local sea level by a few tens of centimetres and most likely, the extra water weight may increase the pressure of fluids in the pores of the rock beneath the seabed. This might be enough for faults to slip.

Even our attempts to stall global warming could trigger a catastrophic event. Scientific community’s untiring efforts to fight the menace of global warming resulted in the concept of carbon sequestration which is basically a composite of geo-engineering techniques developed with a mission for the long-term storage of carbon dioxide or other forms of carbon so that the buildup of carbon dioxide concentration in the atmosphere is reduced. Geological sequestration looks very promising. Bury the carbon dioxide away underground and forget about it. But, geophysicists are concerned that burying the carbon could trigger earthquakes and tsunamis.

In a carbon sequestration power plant (CCS), carbon dioxide is extracted from the exhaust then pumped into aquifers and old gas fields several kilometres beneath the Earth's surface. However, carbon dioxide expands as it rises through the porous rock, increasing pressure inside that may be enough to reactivate a fault and trigger an earthquake. According to Ernest Majer, a seismologist at the Lawrence Berkeley National Laboratory in California, chemical reactions between the injected carbon dioxide, water and rock could also destabilise the rock. Storage sites far from human settlements may also pose threats.

Indeed! We have progressed a lot.