Earthquakes are categorized based on their causes and the tectonic settings where they occur.
1. Tectonic Earthquakes
Tectonic earthquakes are caused by the movement of tectonic plates at fault lines. They are the most common type of earthquakes and occur due to the buildup and release of stress along these faults.
A. Convergent Boundary Earthquakes
At convergent boundaries, plates move towards each other, causing one plate to subduct beneath the other, leading to significant seismic activity.
- Example: 2004 Indian Ocean Earthquake and Tsunami
- Location: Off the west coast of northern Sumatra, Indonesia
- Date: December 26, 2004
- Magnitude: 9.1-9.3 Mw
- Details: This earthquake occurred along the Sunda megathrust, where the Indo-Australian Plate is subducting beneath the Eurasian Plate. It triggered a massive tsunami that affected 14 countries, including India, causing over 230,000 deaths.
B. Divergent Boundary Earthquakes
At divergent boundaries, plates move away from each other, creating new crust as magma rises to fill the gap.
- Example: Earthquakes along the Mid-Atlantic Ridge
- Location: Mid-Atlantic Ridge
- Details: This underwater mountain range is a divergent boundary between the Eurasian Plate and the North American Plate. Earthquakes here are typically less powerful but occur frequently as the plates pull apart.
C. Transform Boundary Earthquakes
At transform boundaries, plates slide past each other horizontally, causing earthquakes due to friction and the release of stress.
- Example: 1906 San Francisco Earthquake, USA
- Location: San Andreas Fault, California, USA
- Date: April 18, 1906
- Magnitude: 7.9 Mw
- Details: This earthquake occurred along the San Andreas Fault, a transform boundary between the Pacific Plate and the North American Plate. It caused widespread destruction in San Francisco and is one of the most significant earthquakes in US history.
D. Intraplate Earthquakes
Intraplate earthquakes occur within a tectonic plate rather than at plate boundaries. They are less common but can be very destructive.
- Example: 1811-1812 New Madrid Earthquakes, USA
- Location: New Madrid Seismic Zone, central USA
- Details: A series of powerful earthquakes struck the central United States, far from any plate boundary. These intraplate earthquakes reactivated old faults and caused significant changes in the landscape.
2. Volcanic Earthquakes
Volcanic earthquakes are associated with volcanic activity and the movement of magma within the Earth. These earthquakes often precede or accompany volcanic eruptions.
- Example: 1980 Mount St. Helens Eruption, USA
- Location: Washington State, USA
- Date: May 18, 1980
- Magnitude: 5.1 Mw (pre-eruption earthquake)
- Details: The earthquake was caused by the movement of magma beneath Mount St. Helens. It triggered a catastrophic eruption that resulted in significant ashfall, pyroclastic flows, and landslides.
3. Induced Earthquakes
Induced earthquakes are caused by human activities such as mining, reservoir-induced seismicity, hydraulic fracturing (fracking), and geothermal energy production.
A. Mining-Induced Earthquakes
Mining activities can destabilize the surrounding rock and cause earthquakes.
- Example: Rockbursts in Mining Areas, South Africa
- Location: Gold mining regions of South Africa
- Details: Deep mining operations have induced seismic activity in South Africa. The sudden collapse of mine roofs can cause rockbursts, which are minor to moderate earthquakes.
B. Reservoir-Induced Seismicity
The filling of large reservoirs behind dams can increase pressure on faults, potentially triggering earthquakes.
- Example: 1967 Koynanagar Earthquake, India
- Location: Koyna Dam, Maharashtra, India
- Date: December 10, 1967
- Magnitude: 6.3 Mw
- Details: This earthquake was induced by the filling of the Koyna Dam reservoir. The increased water pressure reactivated a fault beneath the dam, causing significant seismic activity and damage.
C. Hydraulic Fracturing (Fracking)-Induced Earthquakes
Fracking involves injecting high-pressure fluid into rocks to extract oil and gas, which can induce seismic activity.
- Example: Earthquakes in Oklahoma, USA
- Location: Oklahoma, USA
- Details: Oklahoma has experienced a significant increase in earthquakes attributed to fracking activities and the disposal of wastewater into deep wells. These activities have altered subsurface pressures, triggering earthquakes.
4. Collapse Earthquakes
Collapse earthquakes are small earthquakes that occur due to the collapse of underground caves or mines. These are typically minor and localized.
- Example: Earthquakes in Karst Regions, Slovenia
- Location: Karst regions, Slovenia
- Details: Small earthquakes occur in regions with extensive limestone caves and underground voids, such as Slovenia, where the collapse of these structures can cause minor seismic events.
Conclusion
Earthquakes are caused by various natural and human-induced processes, each with distinct characteristics and impacts. Understanding the different types of earthquakes helps in assessing and mitigating the risks associated with seismic activity. Examples from India, such as the 2004 Indian Ocean earthquake and the 1967 Koynanagar earthquake, and global examples like the 1906 San Francisco earthquake and the 1980 Mount St. Helens eruption, highlight the diverse causes and effects of earthquakes worldwide.
