Why do earthquakes occur? Where and why they are most common is explained by a geologist.

Earthquakes occur daily across various regions, resembling the seams on a baseball. The majority of individuals do not cause any inconvenience to others, therefore their actions do not receive media attention.

 Occasionally, unfortunate events occur where devastating earthquakes strike, causing widespread destruction and immense suffering for those affected. 

According to estimates, a devastating earthquake with a magnitude of 6.3 struck near the historic city of Herat, Afghanistan on Oct. 7, 2023, resulting in the tragic loss of over 1,000 lives in the rubble. Two additional earthquakes, of similar magnitude, occurred on October 11th and October 15th.

 In the Atlas Mountains of Morocco, ancient villages were tragically devastated by a powerful 6.8 magnitude earthquake on Sept. 8, resulting in the loss of nearly 3,000 lives. In February 2023, a significant portion of Turkey and Syria experienced severe devastation due to two major earthquakes occurring in rapid succession. 

As a geologist, I am dedicated to studying the forces that contribute to the occurrence of earthquakes. Allow me to explain the reasons behind the varying levels of seismic activity in different zones. It is worth noting that while some areas experience frequent seismic events, others may remain relatively quiet for extended periods before experiencing a catastrophic event due to accumulated stress. 

The Earth's crust undergoes collisions and separations. 

Earthquakes are a natural occurrence that is inherent to the Earth's behavior. Earthquakes happen due to the movement of tectonic plates, which make up the Earth's outer layer. One can consider the plates as a relatively inflexible outer shell that must move in order for the Earth to release its internal heat. The plates that carry the continents and the oceans are constantly engaged in gentle collisions with one another. 

 In the process called subduction, the oceanic plates gracefully descend beneath the continental plates and return to Earth's mantle. When an oceanic plate sinks, it gently pulls everything along with it and creates a rift elsewhere, which is then filled by hot material rising from the mantle and subsequently cooling. These rifts consist of long chains of underwater volcanoes, commonly referred to as mid-ocean ridges. 

Earthquakes are commonly observed in areas where subduction and rifting occur. Indeed, that is how the plate boundaries were initially discovered. During the 1950s, a global seismic network was established to monitor nuclear tests. Geophysicists made an interesting observation that most earthquakes tend to occur along specific bands. These bands either border the edges of ocean basins, like in the Pacific, or run through the middle of basins, as seen in the Atlantic. 

It has been observed that earthquakes along subduction zones exhibit a shallower depth on the oceanic side, while becoming deeper beneath the continent. When earthquakes are plotted in 3D, they reveal distinct slablike features that correspond to the plates descending into the mantle. A little experiment: Understanding the mechanics of an earthquake 

If you would like to gain a better understanding of what occurs during an earthquake, you may try placing the palms of your hands together and applying a gentle but firm pressure. It appears that you are observing a plate boundary fault. Every hand represents a plate, and the surface of your hands is the flaw. Your muscles can be compared to the plate tectonic system. 

Could you please apply some forward force to your right hand? Eventually, you may notice a sudden forward movement when the force pushing forward becomes stronger than the friction on your palms. Excuse me, but that sudden forward jerk you felt could possibly be an earthquake. Scientists provide an explanation for earthquakes through the elastic rebound theory. 

Plates move at a rather brisk pace of up to 8 inches (20 centimeters) per year, primarily due to the sinking of oceanic slabs at subduction zones. Over time, they gradually adhere to one another due to the friction at the plate boundary. The motion being attempted causes the plate boundary zone to deform elastically, similar to a loaded spring. Eventually, the accumulated elastic energy surpasses the friction, resulting in a sudden forward movement of the plate, which in turn leads to an earthquake. However, the plate-driving forces continue unabated, leading to the accumulation of elastic energy along the plate boundary. This energy may potentially trigger another earthquake, whether it occurs in the near future or further down the line. 

Plate boundaries in the oceans are characterized by their narrow and well-defined nature, which can be attributed to the stiffness of the underlying rocks. However, within the continents, plate boundaries typically consist of extensive areas of rugged mountainous terrain that are intersected by numerous faults. It is possible for those faults to persist for a very long time, even if the plate boundary becomes inactive. That is the reason why earthquakes can sometimes happen in areas that are far from plate boundaries. 

Earthquakes, both rapid and gradual 

Seismologists are able to estimate earthquake risks statistically due to the cyclic behavior of faults. Plate boundaries with rapid motions, like those along the Pacific rim, quickly build up elastic energy and can experience frequent, high-magnitude earthquakes. 

Plate boundary faults that move at a slower pace require more time to reach a critical state. Considerable periods of time, spanning hundreds or even thousands of years, may elapse between significant earthquakes along certain fault lines. This provides ample time for towns to develop and for individuals to gradually forget the collective memory of previous earthquakes. The earthquake in Morocco serves as an example. Morocco is situated on the boundary between the African and the Eurasian plates, which are gradually colliding with each other. 

The vast range of mountains stretching from the Atlas of North Africa to the Pyrenees, Alps, and many other mountains throughout southern Europe and the Middle East is a result of the collision between tectonic plates. However, due to the gradual plate motions near Morocco, the occurrence of large earthquakes is relatively infrequent. 

It appears that Afghanistan has a higher susceptibility to earthquakes. There are several faults that have been caused by the collision of India against Eurasia. The Indian Plate, with its mature and resilient nature, has been steadily colliding with the southern margin of Eurasia for the past 40 million years. One can observe the evidence of this gradual collision by examining the way the mountain chains and earthquakes are positioned on either side of India. 

Getting ready for the major event 

It is worth noting that in the majority of cases, it is not the earthquakes themselves that cause fatalities, but rather the collapse of buildings. 

Many Americans are familiar with California's San Andreas Fault and the potential seismic danger it poses to San Francisco and Los Angeles. In 1989, there was a significant earthquake along the San Andreas Fault at Loma Prieta, located in the San Francisco Bay area. The magnitude of the earthquake, measuring 6.9, was similar to the one in Morocco, but fortunately, the loss of life was significantly lower with only 63 casualties compared to the thousands in Morocco. 

 That's mainly because the building codes in these U.S. cities, which are prone to earthquakes, are now focused on ensuring that structures remain intact during seismic activity. One should note that tsunamis are caused by the shifting of the seafloor during an earthquake, resulting in the displacement of water and the formation of massive waves. The tsunami that struck Japan in 2011 had devastating consequences, regardless of the level of engineering in coastal towns. 

Regrettably, earthquake scientists are unable to provide an exact prediction of when an earthquake may occur; they can only offer an estimation of the potential hazard. 

This article has been updated to include information about another powerful earthquake in Afghanistan. The original publication date was Sept. 13, 2023. 

A Pleasant Discussion Hello, I am Jaime Toro, a Professor of Geology at West Virginia University. This article has been republished from The Conversation under a Creative Commons license. Please take a moment to read the original article. 

Source: citinewsroom.com 

Post a Comment