Earthquake and Its Causes

An earthquake is described as a tremor or movement of the earth's crust that releases energy suddenly and has the potential to cause enormous amounts of damage. An earthquake may occur as a result of natural events like volcanic eruptions or it may be brought on by human activities like mining operations like fracking or explosions (Ostihansk, 2012). The seismic waves that the earthquake creates as it breaks move outward along the surface and through the earth at varying speeds depending on the type of material. The paper investigates earthquakes by concentrating on the main reasons and the manner in which the vibrations occur. The paper will provide valuable information to the undergraduate engineering students and make them understand how earthquakes happen. The students will also be also to get an insight into the reasons that cause earthquakes.

Types of Earthquakes

There are various types of earthquakes depending on the cause and the region where they occur. These types of earthquakes include tectonic, explosion, collapse and volcanic. The tectonic earthquake refers to the type of earth vibration when the earth’s crust smashes as result of geological strengths on the adjacent rocks and plates that cause physical and chemical adjustments (Wang, Shimizu, & Uesu, 2013). Secondly, the explosion quake happens due to the detonation of the chemical or nuclear device. Thirdly, the collapse earthquakes are regarded as small earth vibrations in mines and underground caverns that are due to seismic waves generated by the explosion of rock. Lastly, a volcanic earthquake results from the tectonic strengths that happen in conjunction with volcanic actions (Bouhadad, 2014). Other types of earthquake include the Tsunami, megathrust, harmonic tremor, aftershock, cryoseism, and foreshock. Tsunami earthquake occurs underneath the floor of an ocean occasionally producing enormous sea waves known as tsunamis. The sea waves travel transversely in the ocean with speed of up to 597 miles per hour (960 km), and they could be 49 feet higher when they arrive on the shore (Chen, 2014).

Waves in Earthquake Occurrence

The seismic waves usually travel in two forms of waves which are the P-waves (primary) and the S-(secondary). The P-waves will cause vibrations on the earth’s surface in the regions in which they directly move. These waves travel in an alternating manner like stretching and squeezing patterns of rarefactions and compressions. The P-waves are longitudinal traveling at the speeds of approximately 25,000 km/h (Wang et al., 2013). However, the secondary waves travel at the right angles, but they are slower than the P-waves. Both waves can cause damage, but their research assists in knowing where the earthquake can strike.

Epicenter and Focus of Earthquake

The quake’s focal point or focus is described as the depth from the surface of the earth to the area where the energy of the earthquake originates. The focal depth of an earthquake that emanates from the source to the surface approximately 43.5 miles (70 kilometers) are said to be shallow, those ranging between 43.5 and 186 miles (70 and 300 kilometers) intermediate while those that can go up to about 435 miles (700 kilometers) as deep (Ostřihanský, 2012). The concentration of an earthquake’s focus is on the upper mantle and the crust. The depth that goes to the core of the earth's center is approximately 3,960 miles (6,370 kilometers) (Ostřihanský, 2012). The epicenter is the point on the earth surface that is likely to be affected most by the earthquake.

Liquefaction Process during Earthquakes

Liquefaction occurs when sediments containing water are packed loosely and shakes, thus producing a significant reduction of their strength. This leads to major damages during the occurrence of the earthquakes. For example, during the Loma Prieta earthquake that occurred in 1989, the liquefaction process of the debris and soils utilized to fill the lagoon lead to major fractures, subsidence, and horizontal slides of the ground surface in San Francisco’s Marina district (Wang et al., 2013). The landslides that are triggered by earthquakes usually lead to huge destruction. In the 1964 Alaskan earthquake, the shock-induced landslides devastated the development of Turnagain Heights residence and many of the surrounding regions of downtown Anchorage (Chen, 2014).

Causes of Earthquake

The major causes of earthquakes are categorized into two groups which include the natural and man-made causes. The natural causes of earthquakes include volcanic activity, tectonic movement, interior gasses pressure, dislocation of earth crust and adjustment in the inner rocks (Ostřihanský, 2012). Other causes of earthquakes include folding and faulting in the rock beds, avalanches, and landslides, deposition of materials and denudation of the landmasses.

Tectonic Movement

The tectonic movement takes place when the oceanic plate collides with the continental plate. Tectonic plates are always in constant moves. The oceanic plate is superseded by the continental plate causing the subduction jerky movements along the inclined surface (Bouhadad, 2014). The grinding of two plates creates sudden jolts into completely new locations. Along the faults, the jagged edges of the tectonic plates do grind against each other. The majority of the earthquakes caused by tectonic movement occur in the middle parts of the ocean at the points where the plates push apart on the floor of the sea. The major earthquakes that occur around the edges of large tectonic plates in the Pacific Ocean form an intense regional activity called the “ring of fire” (Chen, 2014). When the grinding happens, massive energy is released from the movement which causes earthquakes. Energy is generated, and the earthquake will continue until when the entire energy gets released from the focus. The structural disturbances that result into a relative displacement of the sections of the lithosphere are termed to be the major causes of earthquake occurrence (Ostřihanský, 2012).

Volcanic Activity

The movement of lava underneath the surface of the earth at the time of volcanic activity causes an earthquake. The occurrence of a volcanic eruption creates void spaces in the mantle and the earth's crust causing a misbalance of the materials (Wang et al., 2013). To create balance on the materials in the mantle, movements happen causing the earthquake.

Dislocation of Earth’s Crust

An abrupt disruption of the crustal segments is responsible for discharging the enormous amount of stored potential energy. The displacement of the segments occurs due to fractures in the crust dislodging from the intense levels of stress. When a dislocation occurs, the crust begins to bend as a result of excessive pressure and stress exerted on it (Chen, 2014). Once the stress in the fault line overwhelms the threshold of the rocks in the crust, an earthquake is produced that is relative in magnitude to its displacement. The rupturing of the crust generates seismic waves, through which the energy is transferred to the surrounding environment (Chen, 2014). The seismic waves then emanate from the earthquake’s source to the surface of the earth. The speed of travel depends on the type of materials through which the waves travel, thus causing vibrations of different intensities. The vibrations cause a “ring like bell” or quiver effect on the earth (Chen, 2014). These dislocations on the earth's crust lead to the formation of one of the primary sources of origin for earthquakes called fault lines. Fractures arise where two slabs of crust glide against one another and interlock forming a mangled ridge.

Adjustment in the Inner Rock Beds

The adjustments of the earth’s inner bedrocks create pressure in the interior of the earth. When adjustments occur on the bedrocks, it is characterized by adjustments between sigma. Beneath the ocean silica and magnesium are present forming the Sigma (Ostřihanský, 2012). The adjustment normally occurs in the interior of the earth's crust and these earthquakes lead to Plutonic Earthquakes. The pressure of gasses formed in the earth’s interior cause expansion and contraction thus instigating sudden shocks that shake the surface.

Man-made Causes

Massive explosions slip occurrence on the steep coasts, and the dashing of the sea waves could lead to earthquakes. Besides, landslides, heavy trucks and huge projects of engineering trigger minor tremors. Moreover, impounding massive amounts of water in the dams disrupts the crystal balance causing the earthquake (Bouhadad, 2014). Also, the shock waves generated via the rock set during the underground testing of hydrogen or atom bombs can lead to a severe earthquake.

Conclusion

In conclusion, earthquakes are phenomenal experiences of sudden movement of the earth crust. Shifting of the earth’s plates results in enormous energy that forms waves causing earthquakes. The occurrence of an earthquake is followed or accompanied by series of vibrations which causes destructions. The major causes of earthquakes include man-made activities, volcanic action, tectonic movement, gasses pressures and adjustment of interior rocks.

References

Bouhadad, Y. (2014). Occurrence and impact of characteristic earthquakes in northern Algeria. Nat Hazards Natural Hazards, 72(3), 1329–1339.

Chen, H. (2014). Research status of tectonic stress and the relationship between tectonic stress and oil-gas accumulation. IOSRJEN IOSR Journal of Engineering, 4(1), 49–52.

Ostřihanský, L. (2012). Causes of earthquakes and lithospheric plates movement. Solid Earth Discuss. Solid Earth Discussions, 4(2), 1411–1483.

Wang, M., Shimizu, K., & Uesu, K. (2013). An Analysis of Earthquakes Latitude, Longitude and Magnitude Data by Use of Directional Statistics. Ouyou Toukeigaku Japanese Journal of Applied Statistics, 42(2), 29–44.