Earthquakes can be so destructive that it is hard to imagine. Every day, thousands of earthquakes occur all over the world; Usually in the form of mild tremors. Many of them are so small that humans cannot feel them.
But sometimes a big earthquake happens. The most recent of them was an earthquake with a magnitude of 7.8 in southern Turkey and Syria on February 6, 2023 (Bahan 17, 1401), which scientists say could be one of the deadliest of this decade. Here are the essential tips about where an earthquake occurs, how to measure its magnitude, and the damage that the largest earthquakes can cause.
Where do most earthquakes occur?
About 80% of all earthquakes on the planet occur along the edge of the Pacific Ocean; where it is also called “Ring of Fire”; Because there are many volcanic activities there. Most earthquakes occur in fault zones; Where tectonic plates—the large pieces of rock that make up the Earth’s top layer—collide or slide together.
These shocks are usually gradual and not felt on the surface, but large stresses can build up between the plates. When this stress is released quickly, it sends large tremors called seismic waves, often hundreds of kilometers into the rocks and into the crust. Other earthquakes can occur far from fault zones; When the plates are compressed or stretched.
Types of faults
There are different types of faults, including normal dip-slip fault, reverse fault and strike-slip fault. In the following, we will see the meaning of each of these errors.
When parts of the Earth’s crust move sideways, the result is horizontal movement along a fault called “extension.”
A famous example is the San Andres Fault in California, USA, which runs about 1,000 km from southern California to northern San Francisco. The lateral movement of the fault branches is caused by the northwestward movement of the Pacific plate under the North American continental crust.
Up and down movements in earthquakes occur in “slope-slip” faults; Where the ground over the fault zone dips (a normal fault) or collapses (a reverse fault). A normal fault occurs where the deeper part of the crust pulls away from a plate beneath it. In the opposite case, we have a reverse fault.
An example of a typical fault is the 240 km Wasatch fault in parts of the states of Utah and Idaho in the United States, again due to the motion of the Pacific plate beneath Northwest America. An earthquake with a magnitude of 7.0 about 550 years ago pushed the ground down about one meter on one side of the fault. The US Geological Survey sees this fault as carrying the risk of another earthquake with a magnitude of 7.0.
Seismologists call faults that have a combination of lateral and up-down movements as strike-slip. For example, the Santa Clara Valley south of San Francisco is seismically subject to oblique motions, as was observed in the 1999 earthquake.
Magnitude rating of earthquakes
Scientists divide the magnitude of earthquakes based on the strength and duration of seismic waves. An earthquake with a magnitude of 3 to 4.9 on the Richter scale is considered small or light; 5 to 6.9 Richter is mild or strong; 7 to 7.9 big Richter; And 8 Richter and higher.
Earthquakes are always followed by aftershocks, which are smaller aftershocks that can last for weeks, or even years in some cases. According to the US Geological Survey, some earthquakes also have foreshocks; Smaller earthquakes that precede a large earthquake.
The largest recorded earthquake was a magnitude 9.5 earthquake that shook southern Chile in 1960. The Valdivia earthquake — named after the city that suffered the most damage — killed an estimated 1,655 people and displaced two million. It also created a tsunami that spread across the Pacific Ocean, inundating the coasts of Japan, Hawaii, and New Zealand.
On average, an earthquake with a magnitude of 8 occurs somewhere every year, and about 10,000 people die in earthquakes every year. Building collapses are by far the leading cause of death, but destruction is often exacerbated by landslides, fires, floods, or tsunamis. Smaller earthquakes, which usually occur in the days after a large earthquake, can complicate rescue operations and produce more death and destruction.
Deaths can be prevented by crisis planning, education, and building houses that sway instead of collapse under the stress of an earthquake.