Overview
This lesson explains what an earthquake epicenter is, how it is determined, and why it is important for understanding and responding to earthquakes.
Earthquakes and Their Causes
- Earthquakes occur due to sudden movement along faults in the Earth's crust.
- The point where the rocks break underground is called the focus or hypocenter.
- The energy released during an earthquake travels as seismic waves.
Epicenter: Definition and Importance
- The epicenter is the point on the Earth's surface directly above the earthquake's focus.
- The epicenter is usually the location where the earthquake's effects are most strongly felt.
- Knowing the epicenter helps in assessing the impact and directing emergency response.
Seismic Waves and Their Types
- Seismic waves are vibrations that travel through the Earth during an earthquake.
- Body waves travel through the Earth's interior and include primary (P) and secondary (S) waves.
- Surface waves travel along the Earth's surface and cause the most damage.
Locating the Epicenter
- Seismologists use data from multiple seismograph stations to locate an earthquake's epicenter.
- The difference in arrival time between P-waves and S-waves at each station is used to calculate the distance to the epicenter.
- By drawing circles with each station at the center and matching the calculated distances, the epicenter is found where the circles intersect (triangulation).
Key Terms & Definitions
- Earthquake — A sudden shaking of the ground caused by movement of tectonic plates.
- Focus/Hypocenter — The point underground where the earthquake starts.
- Epicenter — The point on Earth's surface directly above the focus.
- Seismic Waves — Vibrations released during an earthquake, including P-waves, S-waves, and surface waves.
- P-waves (Primary waves) — Fastest seismic waves that arrive first and move through solids and liquids.
- S-waves (Secondary waves) — Slower than P-waves and only move through solids.
- Triangulation — A method for finding the epicenter using distances from three or more seismograph stations.
Action Items / Next Steps
- Review how to interpret seismograph data and practice locating epicenters using sample problems.
- Read the next lesson about volcanoes for further understanding of earth processes.