Locating Earthquakes

Solid Inner Core

Fluid Outer Core → magnetic field!

Flexible Mantle

Brittle Crust

What's inside the Earth...

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 surfacedirectly above the focus.

Earthquakes send out seismic waves...

...and seismometers detect them on the surface.

Useful characteristics about the waves:

- shear waves- travel up and down- travel slowly- cannot travel through liquid

S Waves

- pressure waves- travel back and forth- travel quickly- can travel through anything

P Waves

Useful characteristics about the waves:

- shear waves- travel up and down- travel slowly- cannot travel through liquid

S Waves

- pressure waves- travel back and forth- travel quickly- can travel through anything

P Waves

Another useful characteristic about the waves:

Since they travel at different speeds, we canfigure out distance to the earthquake.

Another useful characteristic about the waves:

Since they travel at different speeds, we canfigure out distance to the earthquake.

Another useful characteristic about the waves:

Since they travel at different speeds, we canfigure out distance to the earthquake.

Another useful characteristic about the waves:

Since they travel at different speeds, we canfigure out distance to the earthquake.

With distance data from 3 cities, we canfigure 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.

Distance (km) to focus = δt x _____________________(P speed) x (S speed)

(P speed) – (S speed)

(Don't forget to convert to cm on your map!)

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