Tectonics Project Essay
The Ring of Fire is a major area in the basin of the Pacific Ocean where a high percentage of earthquakes and volcanic eruptions occur. Within a 40,000-km horseshoe shape that is casted upon the perimeter of the Pacific plate, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, volcanic belts, and plate movements (Wikipedia, 2017). Four-hundred-fifty-two volcanoes are in this mountain chain that rests atop the basin of the Pacific (What is the “Ring of Fire?”, 2017), and the reason why a large majority of volcanoes are a part of this volcanic mountain chain is due to the constant subduction of the tectonic plates. In addition, many earthquakes are the result of the constant subduction.
Subduction is a geological occurrence that happens when one plate of oceanic lithosphere (the term lithosphere is used to describe the rigid outer part of the earth, which consists of the crust and upper mantle) is forced under another plate (What is the “Ring of Fire?”, 2017). This then resorts to the release of friction sending tremors in P-waves and S-waves.
When two plates collide, they result in earthquakes. And when an earthquake ensues the contact of two or more plates the first wave that is recorded on a seismograph are P-waves, the “p” meaning primary. P-waves are the fastest and strongest seismic wave being able to travel through solid rock and liquid. They travel by vibrating in a fixed direction of propagation called a longitudinal wave (BRAILE, 2007). S-waves on the other hand travel in a series of undulated motions called transverse waves. These waves are the second waves recorded by the seismograph. They also possess a weaker frequency with it only capable of traveling through solid rock rather than a liquid medium and are the aftershock of the P-waves (BRAILE, 2007). When these waves are recorded down they are categorized into different levels of magnitude. The magnitude is used to describe the intensity and relative size of an earthquake with each level being ten times stronger than the previous level. According to Map #1: Earthquake Locations/Magnitudes in 2012
Earthquakes are produced in the three tectonic plate boundaries being the divergent plate boundary, convergent plate boundary, and the transform plate boundary. A divergent boundary occurs when two tectonic plates move away from each other. Along these boundaries, lava spews from long fissures creating new crust. As the magma solidifies it transforms into a dark, dense rock called Basalt (NOAA, 2013). Convergent plate boundaries happen when two plates collide together. When the plates strike, one plate rises upward while the other down. Typically, when this happens a mountain ridge is parallel to the boundary, to the mountain range, and to the trench. Powerful earthquakes shake a wide area on both sides of the boundary (NOAA, 2013). The phenomenon when two plates slide against one another is known as a transform plate boundary. As the plates alternately press in a propagational direction against each other, earthquakes are produced through a wide boundary zone. In contrast to convergent and divergent boundaries, no magma is formed. Thus, crust is cracked and broken at transform margins, but is not created or destroyed (NOAA, 2013).
When one of the three plates create tension, the focal point of an earthquake is determined. The focal point refers to the depth at which an earthquake is initiated. When the depth is between 70 km and 300 km it commonly is classified as mid-focus or intermediate-depth earthquakes. But in subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths in the mantle, ranging from 300-km up to 700-km.