Why does the Earth have an earthquake?

Earthquakes are sudden vibrations of the Earth's surface, often referred to as geodynamic events in ancient times. They are natural phenomena similar to wind, rain, lightning, landslides, and volcanic eruptions, and occur frequently on our planet.

There are multiple causes for the shaking of the Earth’s surface. Based on their origin, earthquakes can be categorized into several types:

1. Collapse earthquakes occur when underground caves or mine roofs collapse. These are usually small and rare, typically found in limestone cavern areas or large mining regions.

2. Induced earthquakes are triggered by human activities such as reservoir impoundment or water injection in oil fields. These happen only in specific locations like reservoirs or oil fields.

3. Artificial earthquakes result from human-induced ground vibrations, such as underground nuclear explosions or controlled blasting.

4. Tectonic earthquakes are caused by the movement and rupture of deep rock formations. These are the most common type, responsible for over 90% of global earthquakes and often have significant destructive power.

5. Volcanic earthquakes occur due to volcanic activity, such as magma movement or gas explosions. They are limited to volcanic regions and account for about 7% of all earthquakes.

Throughout history, people have created many myths and legends to explain earthquakes. In the 12th century, Japanese records mentioned "earthquakes," and in 1710, a Japanese text suggested that giant squids beneath the Earth moved their tails, causing tremors. Similarly, Chinese folklore told of a massive squid underground that would turn over, shaking the land.

In ancient Greece, philosophers like Epicurus believed that trapped winds in the Earth's crust caused earthquakes. Others, like Lukcelushi, proposed that sudden forces or air movements entered the Earth's hollow spaces, creating turbulence and cracks. Aristotle also linked earthquakes to underground winds and burning materials.

By the early 20th century, scientific research into seismic waves began, marking a new era in seismology. Three major theories emerged:

First, in 1911, Reid proposed the "Elastic Rebound Theory," suggesting that when strain energy exceeds rock strength, a fault forms, and the energy is released suddenly, causing an earthquake.

Second, in 1955, Matsuzawa introduced the "Magmatic Impact Theory," explaining that uneven thermal conductivity in rocks leads to expansion and surrounding rock bursts.

Third, Bridgeman suggested that earthquakes could result from sudden changes in underground materials under high pressure and temperature, leading to volume shifts.

Although the full mystery of earthquakes remains unsolved, interdisciplinary research in physics, chemistry, geology, and other fields has significantly advanced our understanding of these powerful natural events.