Earthquakes are one of the most violent forces of nature in existence. It has caused the fall of both structures and infrastructures around the world, forcing a state of calamity in mere minutes. There are no known preventions for these violent tremors of the Earth. Governments and societies all over the globe have only learned to prepare their civilizations for its inevitable occurrence.
What causes these natural yet cataclysmic phenomenons? With nothing to do beyond preparation to counteract this calamity, understanding these forces of nature is vital – especially to citizens who live near fault lines.
What are Earthquakes?
Earthquakes are a natural phenomenon that results from the sudden movement among faults and their lines inside the Earth. Such movement within the Earth unleashes stored energy called ‘elastic strain’ that unravels into the world in the form of seismic waves. These waves circulate throughout the Earth and cause the ground surfaces to shake. Generally, most movements that occur on faults are a response to long-term erosion and deformation and the generation of stress.
Earthquakes are the result of sudden movement along faults within the Earth. The movement releases stored-up ‘elastic strain’ energy in the form of seismic waves, which propagate through the Earth and cause the ground surface to shake. Such movement on the faults is generally a response to long-term deformation and the accumulation of stress.
What Causes Earthquakes?
Whenever a sudden slip happens on faults, it causes earthquakes. The tectonic plates underneath the earth constantly move at a sluggish rate. However, it often happens that they get stuck together due to friction. The hindrance causes a buildup of stress on its edges. When the tectonic movement finally overcomes this friction, the energy is released through an earthquake, causing the waves to move towards the crust that produces the shaking of the ground on the surface.
As seismic waves pass throughout the Earth from powerful earthquakes, seismologists and experts can extract vital information about the internal structure of the planet. It is through these earthquakes the seismic waves are produced. The waves refract and bend as they move to the surface of the earth, similar to the way light interacts with glass prisms. Through the speed at which seismic waves reach the surface and their travel time, scientists were able to discover that the Earth consists of several layers.
Studies on Earthquakes and their Causes
The outermost layer, as discovered by the world’s best minds, is segmented into 15 primary slabs – these are the tectonic plates. The slabs that make up the tectonic plates constitute the lithosphere. The lithosphere consists of the crust – made by continental and oceanic elements – and the upper part of the mantle. The movement of the tectonic plates is relatively slow. However, despite its sluggish movement, usually measured to be only moving a few centimeters a year, still results in massive deformation at the plate boundaries – this causes earthquakes.
Beneath the tectonic plates is the Earth’s asthenosphere. The asthenosphere has a fluid-like behavior over extended scales. A mystery till this very day, there are a variety of competing theories that hope to uncover what exactly it is that causes the movement of tectonic plates. Here are some of the most notable drivers of plate movement:
Mantle Convection Currents – Mantle currents that have heightened temperatures carry the plates of the lithosphere around, similar to the way conveyor belts function.
Ridge Push – When newly developed plates are formed in oceanic ridges, they are warm. This makes them have a higher elevation at the oceanic ridge compared to the colder and denser plate material that is farther in proximity; gravity, then, causes the higher plate at the ridge to push down on the lithosphere that rests further from the ridge.
Slab Pull – This theory explains that older and colder plates sink at subduction zones because, as their temperatures drop, they become increasingly denser compared to the mantle below. These cooler sinking plates pull the warmer ones along as they descend.
Observation of the Earth’s layers has revealed that the majority of earthquakes are connected to tectonic plate boundaries. Through the theory of plate tectonics, field experts have been able to explain the global distribution of earthquakes.
As earthquakes occur, the rock positioned on one side of a fault slips onto or under the other. The fault surfaces are formed in various ways, they can be horizontal, vertical, or even some arbitrary angle in between. Because of the variety in form, faults are classified according to the angle of the fault about the surface – known as the dip – and the direction of slip along the fault.
Earthquakes in the US
Two such plates are located in the area of California — the Pacific Plate and the North American Plate. The Pacific Plate covers the majority of the Pacific Ocean floor and many areas in the California Coastline. The North American Plate encompasses most of the North American Continent and various parts of the Atlantic Ocean floor.
The San Andreas fault is the primary geographical boundary that separates these two faults. This fault extends for over 650 miles and reaches up to 10 miles in depth. There are, however, many more known – albeit smaller – faults in the area. The Hayward fault is in Northern California and the San Jacinto fault branch from San Andreas Fault Zone and enjoins it as well.
The Pacific Plate stretches northwestward, extending past the North American Plate at a rate of approximately two inches every year. Various parts of the San Andreas fault system exhibit the same tendencies through constant creeping that results in several small tremors and a few moderate geological jolts. In areas where this creeping does not produce small earthquakes frequently, the stress on the tectonic plates build-up for years and years on end, eventually producing strong earthquakes when it finally unravels,
The presence of these fault lines results in a higher probability of earthquakes in surrounding areas. It is in these areas where preparation is most needed. In this respect, preparation comes with research. A better understanding of these natural calamities is essential in societies’ preparation efforts.