Upheavels in the Earth
Earthquakes occur when the rock on one side of a fault slips relative to the other. The fault surface can be vertical, horizontal or at an angle
By Tej Singh Kardam
Long ago, a large collection of material masses coalesced and formed the Earth – it was a single crust or plate with no oceans – like a hard-boiled egg. Over time, this single shell or plate started to split and drift into separate plates of land or ocean crusts.
Now the surface looks like spherical jigsaw puzzle, all the plates fit together. The tectonic plates play a crucial role in causing earthquakes which have been occurring throughout Earth’s history, but our ability to document them only goes back to ancient Chinese records.
The earliest recorded evidence of an earthquake dates back to 1831 BC in the Shandong province of China, but the recording began around 780 BC during the Zhou Dynasty.
Plate Tectonics and Faults
The surface of the Earth-the Lithosphere consists of seven major tectonic plates and many smaller ones. The Pacific Plate is the largest, covering one-third of the planet’s surface, active tectonically causing earthquakes and volcanic activity, with collision of European plate and the Philippines plate, resulting in Ring of Fire.
These plates are in constant slow motion in different directions and at different speed from those of neighbouring ones.
Sometimes the plates collide and form mountains. Sometimes two plates move away from one another creating rifts. In another case, two plates move side-by-side, along the same direction or in opposite directions. These three types of inter-plate interactions are the convergent, divergent and transform boundaries.
When the Earth’s tectonic plates move against each other, they put force on themselves and each other. When this stress/force is great enough, the lithosphere breaks or shifts, causing faults. When the break occurs, stress is released as energy, which moves through the Earth in the form of waves called the seismic waves. This causes a sudden shaking of the ground which we call an earthquake.
Earthquakes occur when the rock on one side of a fault slips relative to the other. The fault surface can be vertical, horizontal or at an angle. The faults and seismic waves are the main causes of earthquakes.
World Biggest Earthquakes
Valdivia, Chile, 1960: Was one of the biggest earthquakes near Valdivia (9.5 magnitude). It killed 5,700 people and caused large land subsidence along Chile’s coast, leading to landslides. It resulted due to tsunami waves along the coast and a volcano erupted due to seismic activity, ejecting ash and steam. Lasted 59 days.
Alaska, US, 1964: With 9.2 magnitude, nearly 1,000 km of fault along the Pacific-North American tectonic plate ruptured, causing an earthquake. Shook for nearly 5 minutes, many buildings collapsed and roads sank.
Tohoku, Japan, 2011: With 9.1 magnitude, resulted 18,000 deaths. Was the largest magnitude recorded in Japan.
Kamchatka, Russia, 1952: 9.0 magnitude, epicentre 21.6 km deep, caused tsunami, reached as far as Alaska, Chile and New Zealand. Tsunami killed 15,000 people.
Major Indian Earthquakes
Latur, Maharashtra, 1993: With 6.4 magnitude, having epicentre in Killari village and hypocentre shallow, only 10 km deep. Killed over 20,000 people and destroyed 52 villages.
Gujarat, 2001: Due to high intensity with 7.7 magnitude, tremors felt throughout Northwest India. Bhuj suffered the most as it was close to epicentre. Over 20,000 killed.
Indian Ocean – Boxing Day Tsunami – Sumatra Andaman Earthquake 2004: Epicentre was off the West Coast, northern Sumatra, Indonesia. It was undersea megathrust earthquake at 9.3 intensity. The Indian Tectonic Plate subducted beneath the Burma Plate. Had fault surface of 1,600 km, slipped about 15 metre along the subduction zone. The underwater seismic activity caused tsunami waves 100 ft in height, 15 countries across Southeast and South Asia, parts of East Africa affected. Around 2.5 lakh killed.
Kashmir earthquake 2005: Having 7.6 magnitude, epicentre at the PoK, Pakistan. Felt in India, Pakistan, China, Tajikistan and Afghanistan, killing 80,000 people, injuring 70,000 and displacing 30 lakh.
Surprising scientific/historical facts:
In the opinion of experts of United States Geological Survey, earthquakes can affect the length of a day. In March 2011, 8.9 magnitude, northeast Japan altered the distribution of the earth’s mass, causing it to rotate slightly faster, and shortening an earth day by 1.8 microseconds.
San Francisco city is moving towards LA at the rate of about two inches per year as the two sides of the San Andreas Fault are gradually slipping past one another.
About 90% of the world’s earthquakes occur along ‘Ring of Fire’ in the basin of the Pacific Ocean
In February 2010, 8.8 magnitude, the earth crust was ripped so dramatically that Chilean city Concepcion moved ten feet to the west.
An earthquake in April 2015, (7.8 magnitude) inflicted severe damage to Nepal, causing several Himalayan mountains to shrink, including Mount Everest which shrunk by one inch.
Animals have been observed changing their behaviour prior to an earthquake. Before the Indonesian earthquake and tsunami in 2004, witnesses reported seeing animals and birds heading for higher grounds.
Mitigation and monitoring
The early 1960s marked a very important landmark in the history of seismic monitoring when the World Wide Standardised Seismic Network stations started functioning globally. Monitoring is being done in all continents, especially in countries prone to repeated incidents. But in India the history dates back to 1898 when the seismological observatory of the country was established at Alipore, Calcutta, on 1 December 1898 after the great Shillong plateau earthquake of 1897.
Geo-scientists and researchers at the University of Texas, Austin, have been making continuous efforts to improve forecasting, especially in areas of major subduction zones, with their AI models.
While the efforts so far in earthquake prediction have not been effective, rapid strides in technology will certainly help in forecasting and mitigating natural disasters.
