Tectonic Boundaries Earthquakes
According to the tectonic plate theory, the Earths lithosphere is made up of oceanic and continental plates. Oceanic plates are composed of heavy basalt rocks, while the continental plates that are made of lighter basalt rocks (Edwards, 2005). This is the main reason why the continental plates are assumed to be floating above oceanic plates. The oceanic plates are the ones that sink towards the mantle. The tectonic plate theory is based on the seafloor-spreading phenomenon described by Alfred Wegener during the 1960s (Agarwal and Shrikhande, 2006). According to seafloor spreading, there are ridges on the seafloor or oceanic plates which moves away from each other. Today, the movement was accounted for the convection cycle in the mantle that causes the plates movements. Each plate moves differently from the others. The movement reveals trenches and ridges that expose plate margins or boundaries. If the plates move apart from each other, the boundary is called divergent margin. If instead, the plates collide or move towards each other, then the margin is known as convergent. If the plates shift horizontally past one another (Edwards, 2005), then the plate margin is identified as transform boundary. The different plate may appear to move independently because they move in different directions. Nevertheless, the movement of one plate affects the others as well.
In divergent boundaries, rifts and valleys occur or develop this is because the rocks forms gap between the boundaries. Divergent boundaries are also called constructive boundaries because it is in these areas that molten lava is able to arise. This process eventually leads to the creation of volcanic islands. Mostly, divergent plates occur in oceanic plates. Thus, most ridges are known as mid-oceanic ridges. It also leads to the widening of the oceanic floor. According to Siverstein and colleagues (1998), the plates moves about 2.5 cm. per year. Since new molten rocks filled the ridges, these rocks are noted as younger than the rocks that are far from the ridge are.
The next type of boundary is the convergent margins. These are also known as the destructive boundaries because in these margins two tectonic plates collide. Different tectonic plates converge. When the oceanic and the continental plate converge, the heavier oceanic plates are pushed downwards. The place of convergence is called the subduction trench. The continental plate would form folds of rock or uplift the rock formation and produce mountain ranges. Both oceanic plates could also converge forming deep trenches under the ocean. For example, the convergence between the Pacific oceanic plate and the Philippine plate resulted to the Marianas Trench. Moreover, it could also produce a series of volcanic islands called island arcs.
Continental plates could also converge. Since both are light, the tendency is to push the rocks upward creating highlands like the Himalayas and Tibet (Agarwal and Shrikhande). This is largely due to the fact that the rocks in the boundary were crushed because of the colliding pressure and results to sediments that compressed and uplifted towards the surface. Ulmschneider, highlighted that the creation of mountains through this process in called orogeny.
The last type of boundaries happens when the plates slides horizontally. One plate grinds the other in a sliding motion. This result to high amounts of friction, pressure and strain that could only be released as earthquakes. In California, San Andreas Fault is the plate boundary between the North American plate and the Pacific plate.
Earthquakes are common between plate boundaries because these are the areas where the plates moved due the convection cycle in the Earths mantle. Simon Ross (1998) explained that that earthquakes are sudden release of energy deep underground. The point where the energy was released is called focus. From this particular point, series of shock waves would follow from under the ground. At the surface, directly above the focus or source of shock is the epicenter or the surface center of the earthquake. The shock waves are more commonly known as seismic waves. Seismic waves are either body waves or surface waves. Body waves originated beneath the Earths surface. The other form of seismic wave was the surface waves. Body waves, according to Pankaj Agarwal and Manish Shrikhande (2006) could either be compressional waves (P waves) or shear waves (S waves). The P waves moves in different courses while S waves moves only perpendicularly.
According to the National Research Council, earthquakes could be measured based on the damaged produced by the seismic waves is called seismic intensity. Pankaj Agarwal and Manish Shrikhande also identified magnitude as a way to quantitatively measure an earthquakes size based on the waves showed in the seismograph (2006). The magnitude of the body waves are based on the highest amplitude indicated by the seismograph.
According to the tectonic plate theory, the Earths lithosphere is made up of oceanic and continental plates. Oceanic plates are composed of heavy basalt rocks, while the continental plates that are made of lighter basalt rocks (Edwards, 2005). This is the main reason why the continental plates are assumed to be floating above oceanic plates. The oceanic plates are the ones that sink towards the mantle. The tectonic plate theory is based on the seafloor-spreading phenomenon described by Alfred Wegener during the 1960s (Agarwal and Shrikhande, 2006). According to seafloor spreading, there are ridges on the seafloor or oceanic plates which moves away from each other. Today, the movement was accounted for the convection cycle in the mantle that causes the plates movements. Each plate moves differently from the others. The movement reveals trenches and ridges that expose plate margins or boundaries. If the plates move apart from each other, the boundary is called divergent margin. If instead, the plates collide or move towards each other, then the margin is known as convergent. If the plates shift horizontally past one another (Edwards, 2005), then the plate margin is identified as transform boundary. The different plate may appear to move independently because they move in different directions. Nevertheless, the movement of one plate affects the others as well.
In divergent boundaries, rifts and valleys occur or develop this is because the rocks forms gap between the boundaries. Divergent boundaries are also called constructive boundaries because it is in these areas that molten lava is able to arise. This process eventually leads to the creation of volcanic islands. Mostly, divergent plates occur in oceanic plates. Thus, most ridges are known as mid-oceanic ridges. It also leads to the widening of the oceanic floor. According to Siverstein and colleagues (1998), the plates moves about 2.5 cm. per year. Since new molten rocks filled the ridges, these rocks are noted as younger than the rocks that are far from the ridge are.
The next type of boundary is the convergent margins. These are also known as the destructive boundaries because in these margins two tectonic plates collide. Different tectonic plates converge. When the oceanic and the continental plate converge, the heavier oceanic plates are pushed downwards. The place of convergence is called the subduction trench. The continental plate would form folds of rock or uplift the rock formation and produce mountain ranges. Both oceanic plates could also converge forming deep trenches under the ocean. For example, the convergence between the Pacific oceanic plate and the Philippine plate resulted to the Marianas Trench. Moreover, it could also produce a series of volcanic islands called island arcs.
Continental plates could also converge. Since both are light, the tendency is to push the rocks upward creating highlands like the Himalayas and Tibet (Agarwal and Shrikhande). This is largely due to the fact that the rocks in the boundary were crushed because of the colliding pressure and results to sediments that compressed and uplifted towards the surface. Ulmschneider, highlighted that the creation of mountains through this process in called orogeny.
The last type of boundaries happens when the plates slides horizontally. One plate grinds the other in a sliding motion. This result to high amounts of friction, pressure and strain that could only be released as earthquakes. In California, San Andreas Fault is the plate boundary between the North American plate and the Pacific plate.
Earthquakes are common between plate boundaries because these are the areas where the plates moved due the convection cycle in the Earths mantle. Simon Ross (1998) explained that that earthquakes are sudden release of energy deep underground. The point where the energy was released is called focus. From this particular point, series of shock waves would follow from under the ground. At the surface, directly above the focus or source of shock is the epicenter or the surface center of the earthquake. The shock waves are more commonly known as seismic waves. Seismic waves are either body waves or surface waves. Body waves originated beneath the Earths surface. The other form of seismic wave was the surface waves. Body waves, according to Pankaj Agarwal and Manish Shrikhande (2006) could either be compressional waves (P waves) or shear waves (S waves). The P waves moves in different courses while S waves moves only perpendicularly.
According to the National Research Council, earthquakes could be measured based on the damaged produced by the seismic waves is called seismic intensity. Pankaj Agarwal and Manish Shrikhande also identified magnitude as a way to quantitatively measure an earthquakes size based on the waves showed in the seismograph (2006). The magnitude of the body waves are based on the highest amplitude indicated by the seismograph.
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