Today classes turned in homework and had some questions answered, then we jumped into applying yesterday's notes on how to find distance from an epicenter to a seismic station based on looking at a seismograph:
By knowing approximate speeds of P & S waves (we used 8km/s and 4km/s), we came up with a basic equation to explain distance from an epicenter:
P-S arrival time delay * 8 km/s = distance in km from earthquake epicenter.
Today we used this knowledge to find distances from an earthquake to three different seismic stations, then drew circles around each station to show where the earthquake could have originated. The first circle wasn't very specific, but when a second circle overlapped, two points could have possibly been the source of the earthquake. A third station's data confirmed which of the two points was the location of the epicenter.
This is a process called triangulation. It is the same technique used by GPS units; they must be within range of 3 satellites to determine the unit's distance from each, which pinpoints a location.
Tomorrow, classes will work to complete the assignment and we'll finish notes on plate tectonics. If you finish early, I will ask some people to help their peers understand/complete the assignment - otherwise you may get started on your assignment for Friday; Read p. 373-378, and p. 378 #2-7. Our Exam will be next Friday.
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