How DO they actually locate earthquakes?

Alternatives to S-P TriangulationHubenthal, M. Taber, M.

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

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

Bisector Steps

1. Mark and measure path between TATO/WAKE2. Find midpoint of path3. Draw bisector perpendicular to path4. Label Bisector with station names5. Determine which side of the bisector was close to

the event.6. Repeat with TATO/YAK7. Repeat with WAKE/YAK8. Repeat with additional stations of your choice

Path

Bisector

TATO

WAK

E

X

Bisector Steps

1. Mark and measure path between TATO/WAKE2. Find midpoint of path3. Draw bisector perpendicular to path4. Label Bisector with station names5. Determine which side of the bisector was close to

the event.6. Repeat with TATO/YAK7. Repeat with WAKE/YAK8. Repeat with additional stations of your choice

Solution

Compare to regional seismicity

Earth is ComplexPREM Model

Earth is ComplexPREM Model

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

In reality

• More data• More complex models• Iterative approach