From time to time we hear the news of earthquake in various parts of world. Recently Turkey suffered an earthquake and at least 50000 reported to have lost their lives. A lot of people wonder why earth quakes happen and why it is mainly in certain parts of the world. If the history of earth is examined, we find that earth quakes had been happening periodically causing loss of human life and tremendous damages to the property.
Previously it has been understood that earthquakes originate within the earth due to shifting masses of rocks, miles below the surface. Seismometer is a device to measure the ground’s movement in an earthquake. The improvised seismometer was invented by the Chinese philosopher Chang Heng in AD132. This comprised of a large urn on the outside of which there were eight dragon heads facing the eight principal directions of the compass. Considering the huge leap in science and technology, we could first invent an early warning system for the onset of earth quake only in 1985. This involved ground based sensors, which alert when the trembling starts. Onset of earthquake corresponds to the sudden energy release in the crust of earth.
In order to grasp the scientific nature of earthquake, we need to learn certain terms frequently used to describe earthquake. Seismic means relating to vibrations of earth or its crust. Epicentre denotes the point on the earth's surface vertically above the focus of an earthquake. Richter scale is meant to measure the intensity of an earthquake. The focus is the place inside Earth's crust where an earthquake originates. Aftershock denotes a smaller tremor wave compared to the one just happened minutes or hours earlier.
To understand details of earthquake, one should study the three layers of earth. They are the crust, the mantle, and the core. The crust is made of solid rocks and minerals. Beneath the crust is the mantle, which is also mostly solid rocks and minerals, but punctuated by malleable areas of semi-solid magma. At the centre of the earth is a hot, dense metal core.
Earth's crust comprises about 95% igneous and metamorphic rocks, 4% shale, 0.75% sandstone, and 0.25% limestone. Analysing the elements, 88% of earth crust consists of oxygen, silicon, aluminium and iron, while another 90 elements make up the remaining 12%. The mantle is the mostly solid bulk of Earth\'s interior. The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is about 1,802 mile thick, and makes up a whopping 84 percent of Earth's total volume. The core of earth contains metal and is very hot. The centre of the Earth is roughly 3,959 miles down. The deepest hole that was ever drilled was the Kola Superdeep Borehole, at 7.6 miles deep. That is tiny 0.19% of the way to the centre of the earth.
Earthquakes can occur anywhere between the earth\'s surface and about 450 miles below the surface. For scientific purposes, this earthquake depth range of 0 - 450 miles and is divided into shallow, intermediate, and deep zones. Over 80 per cent of large earthquakes occur around the edges of the Pacific Ocean, because of the abundance of tectonic plates and area of ocean is more than land.
Earthquake tremors can be felt as far as 60 miles from the epicentre, and the distance is proportional to the magnitude of the tremor on Richter scale. This measures the magnitude of the tremor, and it goes with the name of the inventor. The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded in seismographs. The intensity of earthquake increases in a geometrical proportion with the increasing Richter scale number , which means tremors of scale 2 are not normally felt, and happens more than a million times per year. Richter scale 6 and above causes damage to the property and life depending on the nature of inhabitation and built up area of earthquake. While Richter scale 8 happens once a year, the scale 9 and above happens once in 25- 50 years. The largest recorded earthquake was the Great Chilean Earthquake happened on 22/05/1960, which had a magnitude of 9.5. The earthquake which struck near the city of Antakya on 6th February 2023, measured only 6.4, but the devastation was severe due to the population density and shoddy construction of buildings.
Tremor is caused by sudden breaks of underground rock and the subsequent rapid motion along the fault. This rapid release of energy causes the seismic waves that make the ground shake. While most earthquakes are caused by the slipping of tectonic plates, minor earthquakes can also be caused by volcanic eruptions, collapse of rock formations on earth\'s surface, or underground explosions. Plate tectonics is a scientific theory that explains how major landforms are created as a result of earth’s subterranean movements
There are seven major tectonic plates: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific and South American. The Hawaiian Islands were created by the Pacific Plate, which is the world\'s largest plate at 39,768,522 square miles. Tectonic plates are gigantic pieces of the Earth\'s crust and uppermost mantle. British isles are located in the middle of Eurasian plate, and therefore few earthquakes happen there. Ten most vulnerable countries located in the fault line of tectonic plates are follows; 1) Japan 2) Indonesia 3) China 4) Philippines 5) Iran 6) Turkey 7) Peru 8) US 9) Italy and 10) Mexico. Of all the continents, Antarctica has the least number of earthquakes. However, it is important to remember that small earthquakes can occur anywhere in the world.
Let me examine the magnitude of mortality and devastation of recent earthquakes that had happened from time to time in the history of mankind. In Pakistani administered Kashmir 7.6 Richter scale earthquake struck in 2005 and 76000 people perished. The Sichuan earthquake in 2008 left over 5 million people homeless across the region, and over half of the town of Beichuan in China was destroyed. On December 26, 2004, at 7:59 am local time, an 9.1 Richter scale struck off the coast of the Indonesian island of Sumatra, followed by tsunami killing hundreds of thousand of people.
Since many hours prior to an earthquake the pressure in the crust of earth increases, there will be changes in the seismograph. By then the public health or other arms of government can warn the public to take precautionary measures. Every second of early warning equals saving many lives. Precautionary measures include, staying away from windows and all kinds of unstable structures. Until the tremors subside, one must be in a safe space. To do this, one need to create such a space like squatting under a stable table or surround yourself with stable pieces of furniture. During the tremor, one should not use elevator, run up or down stairs, or use electrical appliances. It is advisable to shut of gas, electricity and water after the initial shock.
As we can see, the majority of mortality and devastation of building occur because of lack of government legislation and lack of enforcement. If the head of a state is corrupt so be the officials in planning department. This has been exemplified by the recent earthquake in Antakya (Antioch) which has been known for incidence of earthquake at least for hundred year. We should learn to live with the havocs of nature.
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