Seismic Epicenter Triangulation

Overview

This lecture explains how to locate the epicenter of an earthquake using seismic wave data and the triangulation method.

Triangulation uses data from three seismic stations to pinpoint the earthquake epicenter.
Each station records the time difference between primary (P) and secondary (S) wave arrivals.
The distance from the epicenter to each station is calculated using the P-S wave arrival difference.
Circles are drawn on a map around each station with a radius equal to the calculated distance.
The intersection point of the three circles indicates the earthquake's epicenter.

There are two main types of seismic waves: body waves and surface waves.
Body waves travel through the Earth's interior and include primary (P) and secondary (S) waves.
Surface waves travel along the ground and include Love and Rayleigh waves.

Example stations: Iloilo, Naga, and Tarlac.
Distance from epicenter to stations (in km) is calculated based on P-S wave arrival times.
The map scale is 1 cm = 100 km, so distances are converted for accurate circle drawing.
Draw circles for each station using the computed radii to locate the epicenter.

Convert real distances to map scale by dividing km by the scale factor (e.g., 520 km ÷ 100 = 5.2 cm).
Mark station locations accurately on the map.
Use a compass (or improvised tool) to draw each circle with the correct radius.
The intersection of all three circles gives the epicenter location.

Epicenter — The point on Earth's surface directly above where an earthquake originates.
Triangulation — A method using three points to determine an exact location.
Seismic Station — A facility that detects and records earthquake waves.
Body Waves — Seismic waves that travel through Earth's interior (P and S waves).
Primary (P) Waves — The fastest seismic waves, recorded first.
Secondary (S) Waves — Slower than P waves, recorded after P waves.
Surface Waves — Seismic waves that travel along Earth's surface (Love and Rayleigh waves).

Practice locating epicenters using triangulation method in your module using provided data and correct map scale.
Review previous notes on types of seismic waves.