Earthquakes are a leading cause of disaster globally. Incidences of earthquakes cause massive human fatalities as well as property destruction. The manifestation of earthquakes is the displacement of landmass or the shaking of the ground that depending on its intensity and area of impact may have resultant effects that include tsunamis or formation of other land features (Steacy, Gomberg, & Cocco, 2005). The sudden shaking of the earth's surface is referred to as an earthquake and is often a result of the passage of seismic waves that has a lasting impact on the earth’s rocks. According to Steacy, Gomberg, and Cocco (2005), seismic waves are often a result of released energy coming from within earth crust that suddenly finds its way through the surface. The size and structure of the earth as a planet have contributed to the development of massive fault lines along with multiple areas across continents with vulnerable regions being landmasses along with major tectonic plates (Field, 2015). It is along such seismic regions between the tectonic plates that global seismic maps have been developed to map out vulnerable earthquake regions along with the seismic centers. The areas along the seismic belts have been categorized as high-risk areas that experience higher levels of energy coming from the epicenter and frequently associated with other tectonic activities such as volcanic eruptions. Earthquakes can either be natural or anthropogenic; the paper describes the natural tectonic processes that lead to the occurrence of earthquakes.
Tectonics
Naturally occurring earthquakes are linked to the tectonic plate movements along with the massive landmasses on the surface. According to Steacy, Gomberg, and Cocco (2005), earthquakes linked with tectonic activity are referred to as tectonic earthquakes that are spurred into motion by the movement of earth's surface plates. Referring to the earth’s crust, the surface structure of water bodies and landmasses leaves it as a patch of landmasses that are constantly moving as a result of the liquefied magma below the crust from the core to the mantle (Field, 2015). It is the heat below the earth’s surface that causes a fluid movement underneath the earth’s surface based on different geological periods. The regions along the plates undergo continuous stress based on friction from a constant collision, friction stress. According to Field (2015), increased levels of friction stress that leads to sudden failure when they surpass the critical friction value (local strength). The increased level of stress at the fault plane causes a violent displacement of the crust around the area releasing elastic strain energy resulting in an earthquake. It is the process that was explained by Fielding Reid and the commonly used theory to discuss the process of earthquakes. Other causes of earthquakes have been documented, including volcanism, flashflood, and human instigated occurrences.
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Elastic-Rebound Theory
Natural tectonic process of earthquake draws from several natural activities involving the release of energy from the earth’s crust either by gravity, the motion of massive tectonic plates, chemical reactions, or earth surface elastic strain. The level of energy released from these sources then leads to a chain of activities that lead to estranged disturbances that lead to displacement or shaking of the earth’s crust. The elastic rebound theory best explains the earthquake process (Steacy, Gomberg, & Cocco, 2005). Formulated by Harry Fielding Reid, in the wake of the rapture of the San Andreas Fault, the theory explained the tectonic earthquake process. Fielding observed that earth tectonic quakes result from the accumulation of energy by rock masses (Field, 2015). The accumulated energy then builds up pressure and stress exerted on the rock layers of the crust.
When the pressure exceeds the rocks there results from a fracture, it is the propagation of these fractures along the rock surfaces along the same direction forming a zone of weakness (Steacy, Gomberg, & Cocco, 2005). The zones of weakness can span along significant landmasses over 500km. With a zone of weakness already formed, the affected landmass then slips into opposite directions. It is the continued pressure along with weak points that lead to irregular movements and the restarting cause vibrations along the fault lines leading to propagated seismic waves (Field, 2015). The fault line rapture releases significant energy along the boundaries of the moving tectonic plates causing a subsequent shift in adjacent landmasses leading to an earthquake along the affected zones.
Volcanism
Volcanism can be credited to tectonic movements and as such the cause of earthquake. Volcanism is related to volcanic activity. Like the movement of tectonic plates, volcanism involves the movement of rocks along fault lines with adjacent rocks slipping to release elastic strain energy stored between the rocks (Steacy, Gomberg, & Cocco, 2005). Unlike the tectonic movement instigated earthquake, volcanism earthquakes may be composed of hydrodynamic energy releasing magma above the crust to form other land features (Field, 2015). Volcanism based on the released pressure from underground magma and pressure may lead to seismic pressure from tectonic processes.
Conclusion
The level of destruction of earthquakes draws significant interest to the need for understanding how adverse earthquake episodes occur. Earthquakes are either natural or human instigated with key triggers being seismic activities, landslides, explosions, floodwater, or collapsing dams. The intensity of earthquakes has always been a key feature in the analysis of earthquakes as it is through the intensity that their destructive impact is measured. The paper has considered a number of factors for the realization of appropriate conditions for the occurrence of earthquake. Important aspects to be considered for earthquake to occur include the presence of fault lines, zones of movement, and underground activity.
References
Field, E. H. (2015). Computing elastic‐rebound‐motivated earthquake probabilities in unsegmented fault models: A new methodology supported by physics‐based simulators. Bulletin of the Seismological Society of America , 105 (2A), 544-559.
Steacy, S., Gomberg, J., & Cocco, M. (2005). Introduction to special section: Stress transfer, earthquake triggering, and time‐dependent seismic hazard. Journal of Geophysical Research: Solid Earth , 110 (B5).
