Types of Earthquakes: Tectonic, Volcanic & Collapse

The 4 main types of earthquakes are: tectonic earthquakes (caused by fault movement), volcanic earthquakes (caused by magma activity), collapse earthquakes (caused by underground collapses), and induced earthquakes (caused by human activities). Most earthquakes are tectonic in origin.

Earthquakes are caused by sudden releases of energy in Earth's crust. The four main types — tectonic, volcanic, collapse, and induced — each have different causes and characteristics.

Tectonic Earthquakes

Tectonic earthquakes are the most common and powerful type, caused by the sudden release of stress that accumulates along geological faults where tectonic plates interact. When friction is overcome, the plates slip suddenly, releasing energy as seismic waves. About 90% of all earthquakes are tectonic.

How it forms: Occur at plate boundaries — convergent, divergent, and transform — where plates collide, pull apart, or slide past each other. Stress builds up along faults until it exceeds the rock's strength.

Examples: 2011 Tōhoku earthquake (Japan, M9.1), 2010 Haiti earthquake (M7.0), 1906 San Francisco earthquake (M7.9)

Volcanic Earthquakes

Volcanic earthquakes are triggered by the movement of magma beneath or within a volcano. As magma forces its way through rock, it generates tremors that seismologists monitor to predict eruptions. These earthquakes are generally weaker than tectonic ones but serve as critical warning signs.

How it forms: Caused by magma rising through fractures in rock, creating pressure. Also caused by the collapse of volcanic structures or explosion of volcanic gases.

Examples: Earthquakes before Mount St. Helens eruption (1980), Kilauea tremors (Hawaii), Eyjafjallajökull (Iceland, 2010)

Collapse Earthquakes

Collapse earthquakes occur when underground caverns or mines cave in. The collapse sends shock waves through the ground, but these earthquakes are typically small and highly localized. They pose a danger mainly to miners and people living above old mine workings.

How it forms: Underground voids — whether natural caves or human-made mines — become unstable. The roof or walls collapse, generating seismic waves.

Examples: Mining-induced collapses in South African gold mines, limestone cavern collapses in karst regions

Induced (Human-Caused) Earthquakes

Induced earthquakes are triggered by human activities such as mining, reservoir filling, wastewater injection, hydraulic fracturing (fracking), and nuclear explosions. Oklahoma, USA experienced a dramatic increase in earthquakes due to wastewater injection from oil and gas operations.

How it forms: Human activities change the stress distribution in the crust. Injecting fluid underground lubricates faults; the weight of large reservoirs can trigger nearby faults; mining removes support from rock above.

Examples: Oklahoma earthquake swarms (2009-2016), earthquakes near reservoirs like Zipingpu Dam (China), nuclear test-induced quakes

Explosion Earthquakes

Explosion earthquakes are caused by the detonation of nuclear or chemical explosives. Underground nuclear tests produce detectable seismic waves that can be distinguished from natural earthquakes. The Comprehensive Nuclear-Test-Ban Treaty uses seismic monitoring to detect clandestine nuclear tests.

How it forms: Massive underground explosions send shockwaves through the rock. Seismologists can identify explosion earthquakes by their characteristic wave patterns (strong P-waves, weak S-waves).

Examples: Soviet Tsar Bomba test (1961), US underground nuclear tests in Nevada, North Korean nuclear tests detected seismically

Key Facts

• About 500,000 detectable earthquakes occur each year; about 100,000 can be felt.
• The largest recorded earthquake was the 1960 Valdivia earthquake in Chile (M9.5).
• Earthquakes can trigger secondary hazards: tsunamis, landslides, fires, and liquefaction.
• Most tectonic earthquakes occur along the Pacific Ring of Fire.

Fun Facts

• Animals often behave strangely before earthquakes — dogs howl, fish jump, and snakes emerge from burrows.
• The 2011 Japan earthquake was so powerful it shifted Earth's axis by about 17 cm.
• Moonquakes occur on the Moon, triggered by tidal forces from Earth.

Summary

Understanding earthquake types helps seismologists predict hazards and engineers design safer structures. While tectonic earthquakes dominate, volcanic and human-induced earthquakes are increasingly important to monitor.