Types of Earthquakes

Earthquakes, one of the most powerful and awe-inspiring natural phenomena, have been shaping the Earth’s landscape and influencing human history for millennia. These ground-shaking events occur when there is a sudden release of energy in the Earth’s crust, resulting in seismic waves that can cause devastating destruction. The study of earthquakes, seismology, has revealed that there are different types of earthquakes, each with its unique characteristics, causes, and impacts.

Tectonic Earthquakes

Tectonic earthquakes, also known as natural earthquakes, are the most common type and occur due to the movement of tectonic plates. The Earth’s outer shell, known as the lithosphere, is divided into several large and small plates, and these plates are constantly in motion. When these plates interact with each other, they can either collide, move apart, or slide past each other. The boundaries where these interactions take place are known as fault lines, and it is along these faults that most tectonic earthquakes occur.

• Example: The 2011 Tohoku earthquake in Japan is a classic example of a tectonic earthquake. This mega-thrust earthquake occurred along the subduction zone where the Pacific Plate was forced beneath the North American Plate, resulting in a massive magnitude 9.0 earthquake.

Volcanic Earthquakes

Volcanic earthquakes are directly associated with volcanic activity. They occur when magma, which is molten rock beneath the Earth’s surface, moves and creates fractures or when there is an underground movement of fluids associated with volcanic processes. These earthquakes are often relatively shallow and localized around the volcano.

• Example: The earthquake activity around Mount St. Helens in Washington, USA, is considered a volcanic earthquake swarm. These earthquakes were observed before the volcano’s eruption in 1980, indicating the movement of magma beneath the surface.

Induced Earthquakes

Induced earthquakes, as the name suggests, are triggered by human activities. While most earthquakes occur naturally, human activities such as mining, reservoir-induced seismicity (due to the filling of large dams), geothermal energy extraction, and hydraulic fracturing (fracking) for oil and gas can induce earthquakes. These human-induced earthquakes can occur in regions that are otherwise not seismically active.

• Example: In recent years, Oklahoma has experienced a significant increase in seismic activity due to wastewater disposal associated with oil and gas production, leading to numerous induced earthquakes.

Resonance-Related Earthquakes

Resonance-related earthquakes are a rare type of earthquake that occurs when the seismic waves generated by one earthquake trigger another earthquake on a different fault line. This phenomenon happens due to the similarity in the natural frequencies of the Earth’s crust in both locations. The energy transfer from one earthquake to another can amplify the shaking effect in specific areas.

• Example: The 1992 Landers earthquake in California was followed by the 1999 Hector Mine earthquake, which was likely triggered by the passing seismic waves from the Landers earthquake.

Aftershocks

Aftershocks are not distinct types of earthquakes but are seismic events that follow the mainshock (the most significant earthquake in a sequence). They are smaller earthquakes that occur in the same general area as the mainshock and are caused by the adjustments that the Earth’s crust undergoes following the major release of energy. Aftershocks can continue for days, weeks, or even months after the mainshock.

• Example: After the devastating 2010 Haiti earthquake, the region experienced numerous aftershocks, some of which were strong enough to cause additional damage.

The following table presents comparison of different Types of Earthquakes

Earthquakes are a natural consequence of the dynamic and ever-changing nature of the Earth’s crust. Understanding the different types of earthquakes is crucial for assessing seismic hazards and implementing effective measures to mitigate their impact on human lives and infrastructure.