Introduction
Earthquakes are also referred to as tremblors (Lomnitz, 2013). They are movements that occur in the earth crust causing a build-up of stress at points of weakness known as faults and the deformation of rocks. When they occur, earthquakes cause a lot of destruction. The amount of damage caused is dependent on the magnitude of the quake and the population of the area in which it occurs. Highly populated areas suffer more damages, casualties, and fatalities as opposed to less populated areas (Tucker, Erdik, and Hwang, 2013). This can be ascribed to the findings that a lot of the casualties and fatalities that are associated with earthquakes result for the collapse of buildings. The following paper describes the processes leading to earthquakes and lists some of the most recent earthquakes and their implications.
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Body
Earthquakes are not a rare as the people think. They occur by the thousands daily around the globe. However, they are often in the form of small tremors and therefore, go unnoticed to the individual going about their day to day activities. Some areas are more prone to earthquakes than others. Over 80 percent of all of the world’s earthquakes happen along the Pacific Ocean’s rim that has been dubbed “Ring of Fire” due to the frequent volcanic activity occurring there as well (Zoback and Gorelick, 2012).
To understand how earthquakes occur one must first understand the composition of the earth. The earth is made up of several layers; the crust, mantle, and the core. The crust is the outer layer varying in thickness from 25 to 60 km on the continental surface and 4 to 6 km in the oceanic surface (Higaki and Abe, 2013). The mantle is the middle layer having a depth of about 2890 km. it is a solid layer and therefore, P- and S- waves travel through it. Despite being solid, it has demonstrated fluid behavior, with rocks gradually flowing in large convention cells. The inner section of the earth is the core whose outer part is liquid.
Earthquakes occur when the tectonic plates in the earth’s crust shift and the frictional stress and tension resulting from the gliding plates cause the failure at fault lines. Tectonic plates are massive slabs that make up the upper layer of the earth. The shifting may cause collision of the tectonic plates, a process that happens gradually but leads to a buildup of tremendous stress within the plates (Lomnitz, 2013). A sudden release of this pressure causes massive vibrations known as seismic waves to be sent out hundreds of miles through the earth’s interior and to the surface. Sometimes quakes may also occur in places where there are no fault lines when plates are squeezed or stretched.
While scientists may predict locations where major earthquakes are likely to occur, these predictions are not highly accurate, and the predictions of the timings are difficult to make. Massive earthquakes have led to the leveling of entire cities or affected the whole country particularly those generating tsunamis (Tucker, Erdik, and Hwang, 2013). Earthquakes may also be induced by human activities, for instance, the collapse of a large building or mineral extraction processes from the earth. Nonetheless, in most cases earthquakes caused by human activities are minor.
The magnitude of an earthquake refers to the strength of that quake. The Richter scale developed in 1932 by Charles Richter remains the most commonly used scale for assessing the magnitude of and earthquake (Higaki and Abe, 2013). It was the very first magnitude scale developed. The earthquakes magnitude is obtained by comparing the signals maximum amplitude with the reference event at a particular distance. The scale is logarithmic meaning that the amplitude of an earthquake of magnitude 4 is ten times more than that of magnitude 3 (Higaki and Abe, 2013). Other magnitude scales have been developed based on different seismic wave arrivals. Surface wave magnitude is obtained by measuring surface wave’s magnitude while body wave magnitude is obtained through measuring P wave’s amplitude from far earthquakes.
A magnitude rating is assigned to earthquakes depending on the duration and strength of their seismic waves. Quakes that fall from magnitude 3 to 5 are light, 5 to 7 moderate, 7 to 8 major and eight are massive and consequently cause the most damage (Tucker, Erdik, and Hwang, 2013). An earthquake of magnitude 8 occurs somewhere annually and about 10,000 people succumb to earthquakes each year. While collapsing buildings cause the most fatalities; fires, floods, mudslides and tsunamis often compound the destruction. Smaller earthquakes often termed as tremors usually recur after an earthquake and hamper rescue efforts. They may also cause further damage and death. Governments have resulted to adopting emergency plans and the construction of buildings that sway rather than break in the occurrence of an earthquake in a bid to avoid the loss of life.
Seismic waves
Seismic waves are classified into categories. P waves and S waves. P waves are the primary waves while S waves are secondary waves. Another form of seismic wave is generated when P and S waves interact with the internal layers and the earth’s surface. The speed of the waves is influenced by the properties of the rock through which it is traveling. The dense the rock, the faster a wave travels. P waves travel at a rate of about 6 to 7 km per second while that of S waves is about 3.5 to 4 km per second (Zoback and Gorelick, 2012).
P waves are comprised of successive expansions and contractions such as those of sound waves in air. They are the fastest seismic waves. The particles movement in the rocks waves are moving through is parallel to the wave’s direction. S-waves are transverse waves which mean that their particle motion is at a right angle to the direction of movement. They are slow and cannot move through liquids or air.
Earthquake intensity
The intensity of an earthquake is a measure of earthquakes to the effects and damage caused. The intensity of an earthquake reduces with its distance from the epicenter (Tucker, Erdik, and Hwang, 2013). The device used to measure earthquakes is referred to as a seismogram. It records the seismic waves emerging from the quake. Most seismograms are based on the inertia principle that states that suspended masses remain still when the ground moves. The motion between the ground and the suspended mass is then as a measure of the grounds motion. The P wave is the first recorded seismic wave followed by the S wave. The time difference in the arrival time of the two waves is used to find the location of the earthquake from the seismograph (Lomnitz, 2013).
Recent earthquakes
The most recent earthquakes to have occurred include the moderate earthquakes experienced in Japan on September 13th, 2016, where no damages or injuries were reported. A series of earthquakes of magnitude 5.3 were experienced at the Macedonian capital on mid-September 2016 where minor damages and casualties were reported. Other earthquakes that have occurred within the month of September 2016 include the Australian Antarctic Base earthquake of magnitude 6.3, Tokyo’s magnitude 4.9 earthquake, Colombian 6.0 magnitude earthquake and the New Zealand earthquake of magnitude 7.1 that raised a potential tsunami threat. While the above earthquakes did not cause any significant damages or any fatalities, this has not always been the case. For instance the earthquake in Haiti, 2010 of magnitude 7.0 killed over 230,000 people (Tucker, Erdik, and Hwang, 2013). Likewise, the earthquake at Sumatra in 2004 of magnitude 9.3 caused over 280,000 deaths.
Conclusion
Earthquakes can occur naturally, or they can be induced by human activities. They often happen as a result of seismic waves emerging from the earth’s interior due to the movement of tectonic plates within the earth that creates frictional stress and collisions between the plates. Earthquakes can be dangerous and have resulted in a lot of fatalities in the past. Since we cannot avoid or stop earthquakes governments are putting in place disaster management practices for dealing with earthquakes that include the reduction of injuries and fatalities through building earthquake resistant buildings.
- Higaki, Daisuke, and Shinro Abe. Classification of the Geomorphology, Geology and Movement Types of Earthquake Landslides. New York: Springer, 2013. Print.
- Lomnitz, Cinna. Global Tectonics and Earthquake Risk. 5th ed. New York: Elsevier, 2013. Print.
- Tucker, Brian, Mustafa Erdik, and Christina Hwang. Issues in Urban Earthquake Risk. Springer Science and Business Media, 2013. Print.
- Zoback, Mark, and Steven Gorelick. “Earthquake Triggering and Large-Scale Geologic Storage of Carbon Dioxide.” Proceedings of the National Academy of Sciences 109 (2012): 10164–10168. Print.
