Earthquakes: History and Studies
Earthquakes are sudden and unprecedented movements of the earth’s surface that are caused by the abrupt release of energy into the earth’s crust.
The accumulation of this energy and its subsequent release causes seismic waves that lead to dislodgement of underground rocks, causing faults along which earthquakes take place the point from which an earthquake originated is known as the epicenter on the crust and hypocenter from deep inside the earth. Earthquakes can also be caused by human activities.
Earthquakes are historical, and the earliest documented earthquake took place in China in 1411 BC. In addition, earthquakes cannot be prevented, but their effects can be lessened. However, the magnitude and the intensity of the earthquakes can be measured using varied scales. Finally, earthquakes are catastrophic and are known to cause numerous unpleasant effects, including loss of human life and property.
Although people have a tendency to adopt a varied definition of the term earthquake, different scholars and writers have developed varied fashions of definitions to this term.
According to (USGS 2004), an earthquake is an unanticipated and hasty movement of the earth’s surface as a result of unprecedented discharge of geo-energy that has piled up from underneath the earth’s crust for an extended duration.
According to the latter, the plate tectonics that forms the earth are said to be in gradual movement, thus generating some energy. At times, the plates are engaged in a way that they are unable to release the building force. In such a case, the unreleased energy soars to unsustainable extents and this causing the plates to disintegrate, thus leading to the eruption of earth movement and causing the earthquake.
According to John and Kathie, an earthquake is an abrupt release of energy in the earth’s crust that leads to the development of seismic waves that in return, leads to earth movements to quakes (1997).
The seismic waves are said to be caused by breakages in the geographical faults, landslides volcanic activities mine blasts, and natural experiments, hence leading to the occurrence of earthquakes. An earthquake is a tremor that is caused by an impulsive emission of force into the outer surface of the earth that causes seismic waves.
On the earth’s surface, an earthquake is characterized by shaking of the earth and sometimes by rapid earth movement. In situations where the earthquake occurs in or near seas and oceans, it leads to massive displacement of oceanic, thus leading to a tsunami.
As a result of shaking and movement of the earth, the quake comes with massive destruction on the environment, and it can even lead to landslides and volcano eruptions.
In general, the term earthquake is taken to refer to any seismic event, whether innate or caused artificially by human beings which is casualty to seismic waves that are in most cases as a result of breakages and disintegration of the earth surface volcanic eruptions, land movements, mining activities involving strong explosives and explosions caused by artificial nuclear experiments (Madrigal & Alexis, 2008, John and Kathie, 1997).
An earthquake is the shaking of the earth or an earth tremor also referred to as the earth trembler that is caused by an abrupt slip of the thin zone between two pieces of a disintegrated rock that occur when the two plates pulverize and scratch against each other, causing strain on the earth surface and which makes the pieces of rocks together.
What results out of this is the accumulation of energy, which is then released in the form of waves that pass through the rocks. According to the latter, it is these waves that cause the tremor or the shaking that is experienced at the time of the earthquake.
Spence et al (1989), defined earthquakes as the violent vibration of the earth surface that is as a result of energy being released in to the earth crust and whose source is the abrupt dislodgment of parts of the crust, volcano explosion and events that are man steered involving highly explosive experiments such as the nuclear tests.
According to the latter, earthquakes that occur as a result of the earth’s crust dislodgement are the most fatal and destructive both to human life and property. Earthquakes can, however, be classified into two categories depending on the nature of the fault that causes it. This classification categorizes earthquakes into two basic groups, which includes strike- strip earthquakes and dip-slip earthquakes.
A strike-slip earthquake is an earthquake that takes place on an approximately perpendicular fault plane with the rock on one part of the fault glide parallel to the rock on the other side. On the other hand, dip-slip earthquakes occur when the fault is situated at an angle to the crust, and the movement of the rock occurs in up and down oscillations.
In addition, earthquakes can be classified as shallow, intermediate, and deep. This classification is particularly embedded in the focal depth. According to the USGS, focal depth is the distance from the earth’s crust to the point from which the forces of the earthquake begins (2004).
When this distance is approximately 43.5 miles or below, the earthquakes are described as shallow while in the situation. The focal depth lies from 43.5 to 186 miles. The earthquake is referred to as an intermediate earthquake. Finally, earthquakes whose focal debt goes beyond 186 miles will be classified as deep earthquakes. However, most earthquakes occur in the outer part of the earth (crust) and the outer mantle.
According to the most recent scientific research by world-class geologists, there is a great possibility of earthquakes erupting again along previous faults since they are merely points of weakness on the earth’s crust. This means that the release of energy into the earth’s crust is not an assurance that all the strain has been emitted, and hence the area could still be hit by another tremor or aftershocks (John and Kathie, 1997).
Few scientific studies have been conducted about earthquakes (USGS, 2004). To and until 1800, limited factual reports about earthquakes had been documented. In addition, the natural causes of earthquakes were little known. Although some scientific scholars tried to identify these natural causes, the identified causes seemed mythical and unreal based on today’s scientific research.
For instance, one of the ancient myths who sought to explain the causes of earthquakes stated that it was caused by the rushing of air out of caves deep in the inner of the earth (John and Kathie, 1997). According to the latter, the available record concerning earthquakes indicates that the earliest earthquake to have occurred in china in 1177 BC.
Since then, many other earthquakes have been documented, especially in China, during the many years that followed this main earthquake. Consequently, the history of earthquakes in the European continent goes back to as early as 580 BC.
However, they were not documented until the mid 16th century. In America, the first earthquake to have been recorded is dated to have taken place in the late 14th century and in Peru 1471 though the facts about these earthquakes were not documented.
From the onset of the 17th century, well-documented history and facts about earthquakes could easily be found as they were now being published all over the world, although the accuracy and reliability of the information provided therein were questionable as it was at times overstated or halted (USGS,2004).
The most popular earthquake to have been recorded in the history of North America was the series of the earthquake that took place between 1811 and 1812 in a place in Missouri near New Madrid. First, a strong earthquake whose magnitude was estimated to be eight on the richer scale took place on the 16th of December, 1811.
This was followed by another strong earthquake followed on the 23rd of January in the following year. On the 7th of February 1812, a stronger earthquake occurred at the same place. Throughout this period, the aftershocks of the quake were notably continuous and could still be felt several months after the earthquakes.
The earthquakes were so strong that their effects were felt in as far as Boston and Denver. However, its effect on human life and property were not extensive due to the limited population in the affected areas at the time (USGS, 2004).
According to the documented history, the destructive of North America is the San Francisco earthquake that took place in 1906. The earthquake and the fire that it caused claimed close to 700 lives and left the city destroyed to a very great extent. In addition, it left more than 250,000 residents of the city homeless (USGS, 2007).
On March 27th, 1964, an earthquake that had a higher magnitude than the preceding San Francisco earthquake, releasing approximately double the energy that of the former is estimated to have released, occurred in Alaska. Its effects were so extensive that they were felt in an area close to 500,000 square miles. During the earthquake, the regions around the epicenter that fierce that some trees tops were cut off.
In addition, it led to massive loss of lives with close to 114 people perishing in the tragic. Amazingly, the deaths were reported in as far as California-many miles away from the quake’s epicenter. According to John and Kathie, the fatal earthquake to have ever occurred took place in china in 1557 and is estimated to have claimed more than 830,000 human lives (1997).
Although earthquakes are mostly natural occurrences that can take place in any part of the globe, some places are earmarked to be more prone to earthquakes than others. For instance, the Circum pacific belt, a zone that lies along the great pacific ocean, is the world’s most prone to earthquakes and a region in which most of the world’s earthquakes have been witnessed.
According to the geologists’ approximation, close to 90% of the world’s earthquakes have taken place in this region (John and Kathie, 1997). Most earthquakes are caused by a natural factor beyond the control of human beings; thus, it is impossible to prevent then from occurring.
The earthquakes that man is able to prevent are those caused by human activities such as blasting of mines and nuclear experimenting. Nevertheless, the effects of earthquakes can be toned down (Madrigal & Alexis, 2008).
According to the latter, the advancement in technology has particularly made it possible for geologists to effectively and efficiently predict the occurrence of an earthquake with such level of accuracy that individuals are able to put adequate and appropriate measures to lessen the effect of the catastrophe in case it strikes.
Such prediction can help the concerned individuals to evacuate people who live within the area in which the quake is expected to occur. In addition, individuals who anticipate earthquakes can take measures in bracing themselves to lessen their destruction on property.
As such, they will do fix the shelves firmly to the walls, place heavy and bulky item on the floor or at the bottom-most shelves, and transfer fragile items such as glass items to the floor or lowly to avoid breakages, do way with weights items near human inhabitancy, repair faulty electrical wiring to prevent fires in case of the earthquakes among other preparedness measures (John and Kathie, 1997).
The intensity and magnitudes of earthquakes can be measured (Spence et al., 1989). For instance, the magnitude of an earthquake is measured using the Richter scale. This largely relies on the measurement of the seismographs i.e., the height of the oscillation of seismic waves during the earthquake.
The scale’s upper limit is, however, infinitive, and the outcomes approximation of the scale are referred to as the magnitude of the earthquake. In addition, another mode of measurement, modified Mercalli scale, has been used to measure the intensity of the earthquakes, and it relies greatly on the physical and tangible damage of the earthquake.
This scale is made up of twelve increasing levels of intensity, starting from unnoticeable tremors to most calamitous obliteration. The scale also makes use of Roman numbers and hence is not embedded in any mathematical principles, but it is rather a casual measurement subjective to the observable outcomes of the earthquake. (USGS, 2004; Spence et al., 1989)
Earthquakes are the most frightening and destructive occurrences. Although they at times exhibit just limited and less effective tremors, earthquakes of higher magnitudes are, in fact, catastrophic and come with far-reaching adverse effects that are rather incomprehensible. A mention of a word earthquake tends to send shivers down the spines of individuals, especially those who have experienced it hands-on.
The aftermaths of Earthquakes have numerous adverse effects both to human life, property, the ecology as well as the general environment. First, they cause violent trembling of the earth as well as breakages of the earth’s surface. This results in incomprehensible damages to buildings and other immobile infrastructure. The extent of damage depends on the scale and the distance of the item from the hypocenter.
In addition, the area’s geographical and geomorphologic conditions may contribute to either lessening or worsening the extent of the damage. For instance, the ground acceleration, which is the measure of the ground shaking in the event of an earthquake, varies from one region to another. As a result, certain areas can experience a high level of earth tremor irrespective of low-intensity upheaval due to local or site amplification (Madrigal & Alexis, 2008).
In addition, earthquakes have the potential to cause earth movements and violent storms. Such can indeed occur in any part of the globe. The occurrence of such catastrophes will certainly cause massive damages to the environment, property and could lead to deaths in case they occur in an area inhabited by human beings. In addition, earthquakes lead to outbreaks of fires due to the fact that they fault electricity causing electrical shorts and gas fires eruption.
In addition, they disrupt the water supply, making it difficult to control the spread of these fires. As a result, the effect of the earthquake is amplified by the fires, thus pushing the already fragile situation to a worse state (USGS, 2007). According to a report on the San Francisco earthquake of 1906, more people died due to massive fire outbreaks caused by the earthquakes, and not due to the effects of the earthquake itself.
Furthermore, earthquakes are termed s the main source of soil liquefaction. This is a situation where the earth tremor causes the waterlogged soil particles to lose their potency, thus making them change to liquid form. In such a case, structures such as buildings and bridges are likely to sink, tilt, or collapse into the liquefied deposits (Madrigal & Alexis, 2008).
In an earthquake that took place in 1964 in Alaska, for instance, cases were reported of buildings having sunk after the earthquake had liquefied the soil. Indeed, this is a destructive effect of earthquakes (USGS, 2004).
In situations where the earthquake’s hypocenter happens to be in or near large water bodies such as a sea or an ocean, the resultant effect is the emergence of devastating long wavelengths and sea waves that are caused by abrupt and violent movement of water masses referred to as the tsunamis.
In such a case, water moves at a supersonic speed estimated to be between 600-800 kilometers per hour causing extensive damage to sea ecosystem, destructive results to the structures near the sea and may lead to loss of human life in case human beings happen to be caught up in the melee (John and Kathie, 1997).
In addition, earthquakes have been witnessed to cause various problems to general human life such as death, deformities due to earthquake-related injuries, denied access to basic necessities, communication and transportation infrastructures, increased costs in servicing human insurance, collapsing of architecture, among other devastating effects (Madrigal & Alexis,2008).
As such, earthquakes have absolutely no positivism. Worse still, they are sudden and unanticipated in most cases. However, the ability to predict the possibility of their occurrence accurately is a vital step towards success in lessening these negative impacts of earthquakes (Madrigal & Alexis 2008).
John W. and Kathie Watson (1997): .
Madrigal & Alexis (2008) Top 5 Ways to Cause a Man-Made Earthquake. Wired News (CondéNet).
Spence et al (1989). Measuring the Size of an Earthquake: United States Geological Survey.
USGS (2004) Common Myths about Earthquakes.
USGS (2004) Historic Earthquakes And Earthquakes Statistics: Where Do Earthquakes Occur?
USGS (2007), The great San Francisco earthquake of 1906.
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