Locating Earthquakes
What's inside the Earth...
Solid Inner Core
Fluid Outer Core
→ magnetic field!
Flexible Mantle
Brittle Crust
Convective motions in Earth’s mantle:
→ heat transfer from the core
→ hot spots on the surface
→ pressure on tectonic plates
Earth’s Tectonic Plates
The focus, which is below the Earth’s surface,
is where an earthquake occurs.
The epicenter is the point on the Earth’s surface
directly above the focus.
Earthquakes send out seismic waves...
...and seismometers detect them on the surface.
Useful characteristics about the waves:
S Waves
- shear waves
- travel up and down
- travel slowly
- cannot travel
through liquid
P Waves
- pressure waves
- travel back and forth
- travel quickly
- can travel through
anything
Useful characteristics about the waves:
S Waves
- shear waves
- travel up and down
- travel slowly
- cannot travel
through liquid
P Waves
- pressure waves
- travel back and forth
- travel quickly
- can travel through
anything
Another useful characteristic about the waves:
Since they travel at different speeds, we can
figure out distance to the earthquake.
Another useful characteristic about the waves:
Since they travel at different speeds, we can
figure out distance to the earthquake.
Another useful characteristic about the waves:
Since they travel at different speeds, we can
figure out distance to the earthquake.
Another useful characteristic about the waves:
Since they travel at different speeds, we can
figure out distance to the earthquake.
With distance data from 3 cities, we can
figure out where the earthquake occurred.
This is called triangulation.
This is good for a shallow earthquake.
What if it's not shallow?
This is good for a shallow earthquake.
What if it's not shallow?
This is good for a shallow earthquake.
Not as good for a deep earthquake.
To calculate distance to the earthquake...
Arrival times are given in hrs:min:sec
For example, 14:35:27.8 and 14:36:19.6
δt is the difference between those times
In the above example, δt = 51.8 seconds
(P speed) x (S speed)
_____________________
Distance (km) to focus = δt x
(P speed) – (S speed)
(Don't forget to convert to cm on your map!)