OPENING QUESTIONS:
Compare primary (p) waves with secondary (s) waves
Contrast primary (p) waves with secondary (s) waves
LEARNING TARGET: I will be able to calculate the epicenter of an earthquake using seismograph data during today's class
WORDS O' THE DAY:
- Primary (p) waves - Travel through all types of material and arrive first.
- Secondary (s) waves - Only travel through solid rock (not liquids of any sort) and arrive later
- Surface waves - Only travel along the surface of the earth-- they arrive LAST but are most destructive
- focus - The location of an earthquake inside the Earth
- epicenter - The point on the Earth's Surface directly above an earthquake
WORK O' THE DAY:
Please send one of your team up yonder to collect a copy of one each of the following seismic data for each member of your team (and one color graph too, please!):
Finding the arrival of the primary (p) wave is fairly easy. Depending on the actual data, finding the arrival of the secondary (s) wave can be a bit of a chore.
To make life a wee bit easier, I've chose seismographs that make that determination also fairly obvious.
Work with our team to precisely record the arrival time of each of those waves using that data.
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There is a non-linear relationship between the arrival time of primary (p) waves and the arrival time of secondary (s) waves that is well understood. It does change based on the density of the material the earthquake is traveling through.
However a general relationship is often used as shown below (please send another team member to go fetch a copy of two of those per team):
Take a few moments to review that color graph above.
Notice also that I gave you earthquake seismic data from three different locations. "Triangulating" seismic data is no longer done by hand (if in fact it is actually done at all). However understanding the basic method can be *most* helpful.
Work with your team to suggest a method for triangulating the data from those graphs in order to find the epicenter of that earthquake event.
The scale below is approx 1.4 cm = 50. miles
Now let's see how we *might* go about finding the magnitude of such an event.
This method is a nod towards historical methods that were first developed using California quake data. It is generally considered outdated and not particularly reliable but it does help us get an idea of the relationship between various aspects of earthquake waves:
