Overview
This lecture explains how to locate the epicenter of an earthquake using the triangulation method, applying knowledge about seismic waves and basic map skills.
Seismic Waves Recap
- There are two main types of seismic waves: body waves and surface waves.
- Body waves include Primary (P) waves and Secondary (S) waves.
- Surface waves include Love waves and Rayleigh waves.
- P waves travel faster than S waves and are detected first at seismic stations.
Triangulation Method
- The triangulation method locates an earthquake's epicenter using data from three seismic stations.
- Each station draws a circle with a radius equal to the distance from the station to the epicenter.
- The intersection point of all three circles on a map indicates the epicenter's location.
- Time differences between P and S wave arrivals at stations are used to calculate the distance to the epicenter.
Practical Steps for Triangulation
- Needed tools: drawing compass (or pencil and string), ruler, extra pencil/pen.
- Mark the locations of the three seismic stations on the map (e.g., Iloilo, Naga, Tarlac).
- Convert the real distances to map scale (e.g., 1 cm = 100 km).
- For each station, draw a circle with a radius proportional to the computed distance.
- Find the intersection point of the three circles to identify the epicenter (e.g., Batangas).
Key Terms & Definitions
- Epicenter — the point on Earth's surface directly above the earthquake's origin.
- Triangulation — a method using three points to determine a position by intersection.
- Seismic Station — location equipped to detect and record seismic waves.
- P wave (Primary wave) — fastest body wave, arrives first at seismic stations.
- S wave (Secondary wave) — slower body wave, arrives after P waves.
Action Items / Next Steps
- Practice triangulation using your module's data and map scale.
- Gather required materials (compass, ruler, pencil) for next class.