A lot of disasters have befallen the world we are living in since creation. A lot of them has left millions of lives and property wasted and damaged. Some of these disasters were caused by man, while some others lack clear explanation about what caused them. Man has come to classify disasters into two broad categories – Natural and Man-made disasters. According to this classification, the natural ones are the ones resulting from natural environmental factors and earth processes; examples include floods, volcanic eruptions, earthquakes, landslides, tsunamis, tornadoes, drought, hurricane, and other geologic processes. On the other hand, the man-made ones are disastrous events caused directly and principally by identifiable deliberate, accidental or negligent human actions. However, some people still hold the opinion that both natural and man-made disasters are caused by the activities of man on earth, either directly or indirectly. In this article, considering many questions that have come about as a result of the disastrous earthquakes that have struck some parts of our world recently, we are going to specifically look at one of these natural disasters – Earthquake!
What is an Earthquake?
An earthquake is a sudden violent shaking of the ground, causing great destruction that is basically as a result of the sudden release of energy in the earth’s shifting crust thus creating seismic waves. These waves manifest themselves by vibration, rumbling, shaking and sometimes displacement of the ground. Earthquakes happen along cracks in the earth’s surface, called fault lines, and can be felt over large areas. Earthquakes could occur both on land and on the sea. Other words for earthquake are tremor, temblor, or shock.
Possible Causes and Effects of Earthquakes
a) Natural causes:
Movements within the Earth’s crust such as slippage within geological faults, volcanic activity, landslides are the main natural causes of earthquakes. These earth processes cause stress to build up at points of weakness and make rocks to deform. Stored energy builds up in the same way as energy builds up in the spring of a watch when it is wound. When the stress finally exceeds the strength of the rock, the rock fractures along a fault, often at a zone of existing weakness within the rock. While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. The stored energy is suddenly released causing seismic waves that spread out at extremely high speed (about 3-14 km/sec) from the initial point of rupture, the focus, (i.e, the underground point of origin of the earthquake), like ripples on a pond. These waves are what makes the earth to quake, and can travel large distances in all directions. Near the focus, the waves can be very large, making the shaking and vibrations intense and extremely destructive – thrusting up cliffs and making great cracks in the ground. Earthquakes are capable of shifting a city some feet away from its original location on the map. The shift may or may not be significant, depending on the magnitude of the quake.
Earthquakes last just for few moments and by themselves rarely kill people or wildlife. It is usually the secondary after-events that they trigger, such as building collapse, ground rupture, gas line explosions, fires, floods, tsunamis, avalanches, and volcanoes, that actually brings about human disaster and fatalities.
b) Induced Causes
Earthquakes could be induced by human earth activities such as, drilling and injecting liquid into wells, coal mining, oil drilling, mine blasts and nuclear tests, storing large amounts of water behind a dam, and possibly the construction of an extremely heavy building. The best-known example of induced tremor is probably the May 2008 Sichuan earthquake in China’s Sichuan Province which resulted in 69,227 fatalities and is the 19th deadliest earthquake of all time. The Zipingpu Dam is believed to have fluctuated the pressure of the fault 1,650 feet (503 m) away causing a powerful tremor. The greatest earthquake in Australia’s history which hit Newcastle, a city built over a large sector of coal mining areas is also claimed to be induced by humanity, through coal mining. The earthquake has been reported to be spawned from a fault that reactivated due to the millions of tonnes of rock removed in the mining process.
c) Supernatural Causes
i. Religion
Christians generally believe that the occurrence of earthquakes is in fulfilment of the prophecy on the signs of the end time according to Jesus Christ, the Messiah. In His gospel, Christ clearly stated that among other disasters that will befall the earth before His second coming, are earthquakes which He said will occur in divers places. This could be found in the Christians’ Holy book, the Bible. Apart from this prophecy, there were also other occasions recorded in the Bible where earthquakes occurred, such as, at the death of Jesus on the cross, at His resurrection and also when Paul and Silas, the disciples of Jesus were imprisoned. All these were recorded to have happened for significant divine purposes.
ii. Myths
According to Norse mythology, earthquakes were explained as the violent struggling of the god Loki. When Loki, god of mischief and strife, murdered Baldr, god of beauty and light, he was punished by being bound in a cave with a poisonous serpent placed above his head dripping venom. Loki’s wife, Sigyn stood by him with a bowl to catch the poison, but whenever she had to empty the bowl the poison dripped on Loki’s face, forcing him to jerk his head away and thrash against his bonds, which caused the earth to tremble. In Greek mythology, Poseidon was the cause and god of earthquakes. When he was in a bad mood, he struck the ground with a trident, causing earthquakes and other calamities. He also used earthquakes to punish and inflict fear upon people as revenge. Also, in Japanese mythology, Namazu is a giant catfish who causes earthquakes. Namazu lives in the mud beneath the earth and is guarded by the god Kashima who restrains the fish with a stone. When Kashima lets his guard fall, Namazu thrashes about, causing violent earthquakes.
Source of myths – en.wikipedia.org
Kinds, Measurement and Magnitude of Earthquakes
Earthquakes magnitude is an objective measurement of the energy radiated or released by an earthquake. The magnitude of an earthquake is proportional to the area of the fault that ruptures multiplied by the amount of slip on the fault. It is the size and intensity that determines the magnitude. Earthquake is measured using an instrument known as a seismometer. According to size and intensity, earthquakes are majorly classified into three – fore-shock, main-shock and aftershock. Scientists scarcely can tell if an earthquake is a foreshock until a more intense one, the main shock occurs, and any other less intense one that follows is usually regarded as an aftershock. The magnitude or intensity of an earthquake can range from one that is barely felt to ones that are violent enough to toss people around. An 8.6 magnitude earthquake releases energy equivalent to about 10 000 atomic bombs of the type developed in World War II!
Below is a table classifying earthquakes according to magnitude:
| Class | Magnitude | Effects | Estimated Number of occurrence per Annum |
| Great | 8 or more | Great Earthquake. Can totally destroy communities near the epicentre. | Once in 5-10 years |
| Major | 7 – 7.9 | Major earthquake. Serious damage. | 20 |
| Strong | 6 – 6.9 | May cause a lot of damage in very populated areas. | 100 |
| Moderate | 5 – 5.9 | Slight damage to buildings and other structures. | 500 |
| Light | 4 – 4.9 | Often felt, but only causes minor damage. | 30 000 |
| Minor | 3 -3.9 | Same as light. | 90 000 |
| Insignificant | 2.5 or less | Usually not felt, but can be recorded by a seismograph. | unknown |
Table source: pnsn.org
Major and Latest Earthquake Occurrences – Earthquake Prone Areas
A city is most likely to be prone to earthquakes if it is located at the meeting of two tectonic plates, that is, on a seismically active region.
One of the most devastating earthquakes in recorded history was the 1556 Shaanxi earthquake, which occurred on 23 January 1556 in Shaanxi province, China. More than 830,000 people died. Most houses in the area were yaodongs—dwellings carved out of loess hillsides—and many victims were killed when these structures collapsed.
The 1976 Tangshan earthquake, which killed between 240,000 to 655,000 people, was the deadliest of the 20th century.
The 1960 Chilean Earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitudes on 22 May 1960. Its epicentre was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday Earthquake (March 27, 1964) which was centred in Prince William Sound, Alaska.
Some of the most significant earthquakes in recent times include:
- The 2004 Indian Ocean earthquake, the third largest earthquake recorded in history, registering a moment magnitude of 9.1-9.3. The huge tsunamis triggered by this earthquake killed at least 229,000 people.
- The 6.9 magnitude 2005 Azad Jammu & Kashmir and KPK province Earthquake, which killed or injured above 75,000 people in Pakistan.
- The 7.7 magnitude 2006 Pangandaran earthquake and tsunami.
- The 7.9 magnitude May 12, 2008, Sichuan earthquake in Sichuan Province, China. Death toll at over 61,150 as of May 27, 2008.
- The 8.8 magnitude February 27, 2010, Chile earthquake and tsunami cost 525 lives.
- The 2011 Tōhoku earthquake and tsunami registered a moment magnitude of 9.0. The earthquake and tsunami killed 15,889 and injured 6,152. 2,609 were still missing as of 2014.
- The latest earthquake that struck is that of 25th April and 12th May 2015 which consecutively hit the country of Nepal, in Asia, and claiming more than 8 000 lives.
Possible Forecasts and Ways of Prevention
The occurrence of an earthquake has remained unpredictable till present day. Scientists have tried many different ways of predicting earthquakes, but none have been successful. Based on the location of a city, on any particular fault, scientists are always able to say there will be another earthquake sometime in the future, but they have no way of telling when it will happen. The only precautions that are possible for the time being is by better building construction, safety systems, early warning and planning. The popular phrase, “Drop, Cover, and Hold-on” is recommended during an earthquake as a safety measure, though it provides very little escape.
With the rapid growth of mega-cities such as Mexico City, Tokyo and Tehran, in areas of high seismic risk, some seismologists are warning that a single quake may claim the lives of up to 3 million people.
Diagram showing the processes of an earthquake
