Labs / Geography
Locate the Epicenter
Each station's seismogram records a fast P wave, then a slower S wave. The wider that S − P gap, the farther the quake — so every station draws a circle it must sit on. Drag the three stations and watch the circles cross to fix the epicenter, then flip the reveal to see how close you got.
A —B —C —fix —err —
What to try
- Why does one crossing point of three circles pin down the epicenter, when two circles alone leave you guessing between two spots?
- Drag the stations into a tight cluster. Why does the fix get so much shakier than when they surround the quake?
- Line all three stations up in a row. What happens to the estimate, and why is station geometry as important as the readings themselves?
- Crank up the reading noise. How many kilometres of error does a one-second mistake in the S − P time create?
- Which station shows the smallest S − P gap — and is it always the one closest to the hidden epicenter?