A Guide of Earthquakes

By Yufan Hu

What happens in an earthquake

An earthquake occurs when there's a sudden release of energy in the Earth's crust, creating seismic waves. This release of energy usually results from the movement of tectonic plates - either sliding past each other, moving away, or colliding. The point where this energy is released underground is called the focus, while the point directly above it on the surface is the epicenter. Earthquakes can cause the ground to shake vigorously, leading to the collapse of buildings, landslides, tsunamis, and other catastrophic events depending on their magnitude and proximity to populated areas. The intensity and damage of an earthquake depend on factors such as the depth of the focus, the geological conditions that may amplify ground motion, and the structures' design and resilience on the surface.

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The Science of Earthquakes

How and Why Earthquakes Occur:

Earthquakes are the Earth's natural way of releasing stress that accumulates at tectonic plate boundaries. When plates slide past, collide, or move away from each other, the energy released can cause the ground to shake.

3 Types of Waves

  • Primary (P) Waves: Fast-moving waves that compress and expand the ground.
  • Secondary (S) Waves: Slower waves that move the ground up and down or side-to-side.
  • Surface Waves: These waves travel along the Earth's surface and cause most of the shaking felt during an earthquake.

Measuring Earthquakes

The Richter Scale and the Moment Magnitude Scale: The Richter Scale, though historically significant, has been largely replaced by the Moment Magnitude Scale, which more accurately measures the energy released by an earthquake.

Seismographs: Instruments that detect and record the vibrations caused by earthquakes, providing crucial data for understanding their strength and origin.

Major Earthquakes Throughout History

Here is a more comprehensive map!

Where do earthquakes usually occur?

Earthquakes primarily occur along the boundaries of the Earth's tectonic plates, especially in the following eight zones:

Japan Case Study

Japan was hit by an earthquake with a magnitude of 8.9 in March 2011. The subduction zone was along the Pacific Plate and the Eurasian Plate and they moved 5-8km. This happened 130km off the coast of Japan. It was a shallow focus earthquake and it caused a 10m tsunami. The coast became a muddy swamp, 27,000 people were killed and there was damage to the nuclear plant at Fukashima. 160,000 people were left homeless

Earthquake Prediction

Seismic gaps, Tiltmeters, Radon gas, Lasers, Animal behavior, Levels of water in wells

Earthquake Early Warning Systems (EEWS)

EEWS are real-time systems that detect the initial energy release of an earthquake, providing precious seconds to minutes of warning before the more destructive waves arrive. Countries like Japan, Mexico, and the United States have implemented these systems to trigger alarms, halt trains, and manage utilities, potentially saving lives and reducing damage.

Here is what you SHOULD do to protect yourself in an earthquake

Drop, Cover, and Hold On - Protect Yourself During an Earthquake