Focal Mechanism Inversion

Notebooks: codes/focal_mechanism.ipynb

Fault plane

Focal Mechanism Beachball

Radiation pattern

Kumar et al. (2016)

How to determine focal mechanism?

Review: Inverse Problems in Geophysics

  • Forward function: last lecture
  • Objective/Loss function
  • Gradient
  • Optimizer
Kumar et al. (2016)

Focal mechanism from first motion polarity

  • FPFIT

Objective/Loss function:

are the observed and theoretical first-motion polarity (0.5 for compression, -0.5 for dilatation).
is the square root of the normalized theoretical P-wave radiation amplitude of earthquake recorded at the station for source model .

Reasenberg (1985)

Focal mechanism from first motion polarity

  • HASH
Hardebeck and Shearer (2002)

![](./assets/Screenshot%202023-10-29%20at%2014.49.33.png)