1. How DO they actually locate earthquakes? Alternatives to S-P Triangulation Hubenthal, M. Taber, M.

2. An Inverse Problem We know the end product; arrival times We have a velocity model for Earth and we want to calculate the original event – Location – Origin time Forward Problem = Model parameters → Data Inverse Problem = Data → Model parameters

3. The bisector method P arrivals are much easier to pick Assumes an extremely simple velocity model Which station of this record section was closest? 1 2 3 4 5 6

4. Bisector Steps 1.Mark and measure path between TATO/WAKE 2.Find midpoint of path 3.Draw bisector perpendicular to path 4.Label Bisector with station names 5.Determine which side of the bisector was close to the event. 6.Repeat with TATO/YAK 7.Repeat with WAKE/YAK 8.Repeat with additional stations of your choice

5. Path Bisector TATO WAKE X

6. Bisector Steps 1.Mark and measure path between TATO/WAKE 2.Find midpoint of path 3.Draw bisector perpendicular to path 4.Label Bisector with station names 5.Determine which side of the bisector was close to the event. 6.Repeat with TATO/YAK 7.Repeat with WAKE/YAK 8.Repeat with additional stations of your choice

7. Solution

8. Compare to regional seismicity

9. Earth is Complex PREM Model

10. Earth is Complex PREM Model

11. Solution to complexity Iterative approach – Solution through the model provides result – Result is run back through the model to see if it matches the observations (forward problem) – Differences used to refine the model to compute a new solution. – Process continues until some condition is met

12. In reality More data More complex models Iterative approach