Some of the most catastrophic natural dangers – tsunamis, earthquakes, and volcanic eruptions – are usually connected with tectonic plate boundaries (Duarte and Schellart 1). Their emergence has caused a debate in the scientific world about their physical origins and their allocation within time and space dimensions.
The 1755 great Lisbon earthquake was the first prompt for studying the internal structure of Earth and the advancement of seismology (Duarte and Schellart 1). However, at that time the scientists did not have the appropriate knowledge and equipment to check their theories of plate boundaries. Only two hundred years later, the notion of “rigid plates” and “associated plate boundaries” appeared (Duarte and Schellart 1). The theories of Wegener (1912), Holmes (1931), and Wilson (1963) represented the earliest ideas of the continental drift (Duarte and Schellart 1). Wilson’s further contribution was correlating the earthquake types with the kinds of motion along the tectonic plate boundaries. In 1967, Jason Morgan represented a global tectonic model comprising twelve plates. A few months later, Le Pichon proposed a reduced model of just six plates (Duarte and Schellart 1). At that period another significant opening was made. The scientists identified three kinds of plate boundaries: “normal, thrust, and transform” (Duarte and Schellart 1).
The present-day understanding of plate tectonics is reflected via the Earth’s surface consisting of rigid lithospheric plates. These plates include the “crust” and the “upper portion of the mantle,” and they move consistently related to each other over the asthenosphere. At the plates’ boundaries, seismicity, deformation, and volcanism may appear (Duarte and Schellart 1). The asthenosphere is the high-temperature, low-thickness part of the uppermost mantle which produced a little mechanical obstruction to the plate movement. Usually, plates are a hundred-kilometer thick, and their movement is limited to just a few centimeters each year (Duarte and Schellart 1). The rigid plate type was used to estimate the present and past plate movement.
However, soon the scientists learned that plate boundaries differ in various areas. While in some places, plate boundaries are narrow, in other regions they may be represented by deformation spreading for hundreds of kilometers (Duarte and Schellart 1). The plate rigidity is still applied by the scientists, but the modern space geodetic methods make it possible to calculate the intraplate strain. Thus, it is possible not only to measure the corresponding movement of the tectonic plates inside and outside of the boundary zones but also to estimate their deformation (Duarte and Schellart 1).
Plate boundaries comprise fifteen percent of the surface of Earth, and they are classified into three kinds: “divergent, convergent, and transform” (Duarte and Schellart 1). Within the divergent type, plates drift away from one another. These plate boundaries’ volcanic and seismic characteristics are low or moderate (Duarte and Schellart 1). Convergent plate boundaries are represented by the plates moving in the direction towards one another. Within the transform boundaries, two plates drift past each other without any meaningful merging or disparity. In this type, the lapse between the plate boundary defect has a principally horizontal flow (Duarte and Schellart 1-5).
Forty percent of the world’s population lives within the plate boundary zones, which represent the areas of some of the most dangerous natural risks (Duarte and Schellart 6). The tectonic plate boundaries frequently are the causes of geophysical natural hazards, such as earthquakes, tsunamis, and volcanoes.
Work Cited
Duarte, João C., and Wouter P. Schellart. “Introduction to Plate Boundaries and Natural Hazards.” Plate Boundaries and Natural Hazards, edited by João C. Duarte and Wouter P. Schellart, Wiley, 2016, pp. 1-10.