The Geological Engine of South America
South America is one of the most seismically active regions on the planet. Thousands of earthquakes are recorded each year, although most are imperceptible. But why does it shake so much? The answer lies in tectonic plates, enormous blocks of the Earth's crust that move slowly and collide with each other.
In this region, the Nazca Plate moves eastward and slides beneath the South American Plate in a process called subduction. This phenomenon is the main cause of earthquakes and the formation of the Andes mountain range.
What Are Tectonic Plates?
The lithosphere, the Earth's outermost and rigid layer, is fragmented into about 15 major plates that float on the mantle. These plates move at speeds of a few centimeters per year, driven by convection currents in the mantle.
There are three types of plate boundaries:
- Convergent: two plates collide and one sinks beneath the other (subduction).
- Divergent: plates move apart and create new crust.
- Transform: plates slide past each other laterally.
In South America, the convergent boundary between the Nazca and South American plates is the most significant.
Subduction: The Origin of Earthquakes
When the Nazca Plate sinks beneath the South American Plate, enormous stresses build up in the contact zone. The accumulated friction is suddenly released as seismic waves, causing earthquakes. This continuous process explains why the Pacific coast of Colombia, Ecuador, Peru, and Chile is so prone to large-magnitude earthquakes.
A clear example is the 1960 Valdivia earthquake in Chile, the strongest ever recorded at magnitude 9.5. Also, the 2007 Pisco earthquake in Peru, with a magnitude of 8.0, left thousands of victims.
Other Plates Influencing the Region
Although the subduction of Nazca is the main source of earthquakes, other plates also play a role:
- Caribbean Plate: interacts with the South American Plate in northern Colombia and Venezuela, generating earthquakes such as the one in Cúcuta in 1875.
- Scotia Plate: in the far south, near Antarctica, produces seismic activity in Patagonia and the Falkland Islands.
- South American Plate: although it is the main plate, its eastern boundary with the African Plate (divergent) is less seismic.
Why Are Not All Earthquakes the Same?
The magnitude and depth of an earthquake depend on the rupture zone and the type of movement. In subduction zones, earthquakes can be shallow (less than 70 km), intermediate (70-300 km), or deep (more than 300 km).
For example, the 1994 Bolivia earthquake, of magnitude 8.2, occurred at a depth of over 600 km and caused less damage than a shallow earthquake of lower magnitude. Shallow earthquakes are more destructive because they release energy near the surface.
The Threat of Tsunamis
Subduction earthquakes with epicenters in the ocean can displace the seafloor and generate tsunamis. South America has a tragic history: the 1868 tsunami in Arica (Peru/Chile) and the 2010 tsunami in Chile, which devastated coastal areas.
Therefore, early warning systems in countries like Chile and Peru are essential to evacuate the population in time.
How to Measure and Predict Earthquakes?
Seismographs record seismic waves and allow calculation of magnitude (Richter or moment magnitude scale). However, predicting the exact moment of an earthquake remains impossible. What is done instead is to assess the seismic hazard of an area through geological and historical studies.
In South America, countries like Chile, Peru, and Ecuador have monitoring networks and risk maps that aid urban planning and public preparedness.
Tips to Be Prepared for an Earthquake
Living in a seismic zone implies adopting a culture of prevention. Here are some practical tips:
- Identify safe spots in your home, such as under sturdy tables or door frames.
- Prepare an emergency kit with water, non-perishable food, flashlight, radio, and documents.
- Secure shelves and heavy objects to walls to prevent falls.
- Conduct evacuation drills with your family or community.
- Stay informed through apps like Contingencias, which alert you to earthquakes and other phenomena.
Conclusion
South America shakes because the Nazca Plate subducts beneath the South American Plate, an inevitable geological process. Understanding the causes and being prepared is key to reducing the impact of earthquakes. Science advances, but prevention remains our best tool.