NONOGRAM PRACTICE
HOW TO LOCATE
AN EPICENTER
WHAT IS AN EPICENTER?
•  A point on the surface of the Earth directly above the
FOCUS of the earthquake.
• The point within the Earth from which
earthquake waves originate.
Why are P-waves considered primary waves
and S-waves considered secondary?
Miles away from the earthquake’s epicenter,
P-waves are the first to hit (primary) because
they travel faster. S-waves hit slightly later
(secondary) because they’re a little slower.
How can you tell how far away the epicenter really is?
Let’s practice together!
USE THE DATA FROM THE RECORDING STATIONS:
•  Station A: San Francisco, California
P-Wave arrival 3:02:20
S-Wave arrival 3:06:30
What is the time
difference
between P and
S wave arrivals?
USE THE DATA FROM THE RECORDING STATIONS:
•  Station B: Denver, Colorado
P-Wave arrival 3:01:40
S-Wave arrival 3:05:00
What is the time
difference
between P and
S wave arrivals?
USE THE DATA FROM THE RECORDING STATIONS:
•  Station C: Missoula, Montana
P-Wave arrival 3:01:00
S-Wave arrival 3:03:00
What is the time
difference
between P and
S wave arrivals?
DIFFERENCE IN ARRIVAL TIMES (LAG TIME):
San Francisco: 4:10 min.
Denver, Colorado: 3:20 min.
Missoula, Montana: 2:00 min.
Station A: ΔT = 40
seconds
390 km
Distance = ______
Station B: ΔT = 65 seconds
635 km
Distance = ______
Station C: ΔT = 33
seconds
320 km
Distance = ______
DIFFERENCE IN ARRIVAL TIMES (LAG TIME):
San Francisco: 4:10 min.
Denver, Colorado: 3:20 min.
Missoula, Montana: 2:00 min.
2,800km
2,000km
1,100km
USING THE DISTANCE FROM THE STATION TO THE
EPICENTER:
San Francisco: 4:10
= 2,800km
5,000
4,000
3,000
2,000
1,000
Open your compass to
the EXACT distance on
the scale.
USE YOUR CAREFULLY SET COMPASS TO DRAW
A CIRCLE AROUND EACH CITY.
.
.
2,800km
.2,000km