triangulation finding earthquake’s epicenter using seismograms! in class activity (working with...
TRANSCRIPT
Triangulation
Finding earthquake’s epicenter using seismograms!
In Class Activity (working with shoulder partner is A – OK!)
• Focus – the place deep in the crust where the earthquake begins (source of primary and secondary waves)
• Epicentre – the surface location directly above the focus (source of surface waves)
Let’s say station #1 knows the earthquake happened 200 kms away.
But 200 kms in what direction?
If a second station reports it as 75 kms away, they can draw a circle and see where it
intercepts the first circle.
But that still doesn’t pinpoint the location – it could have happened at either spot where the
two circles touch.
But a third station removes all doubt as to where it happened.
Three seismographs are needed to pin- point the source of an earthquake.
• Nomograph
Finding Magnitude
In class activity
• We’re going to find an epicentre of an earthquake in San Francisco
• Lesson 12 http://maccallum.wikispaces.com• Paper and Pencil activity• Let’s do 1st one together! Walk through it.• You and shoulder partner can quietly work on
the last 2 seismograms• What is the average magnitude of this San
Francisco earthquake? • Please raise hand when finished.• If I saw your work, you can try the links at the
bottom of wikispace (Virtual Earthquake)