Summary

•  Different kinds of seismic sources

•  Green’s function and Representation Theorem

•  GFs for several important cases –  Acoustic, homogeneous whole space, explosion

–  Elastic homogeneous whole space, point forces

Stokes, 1849

Earthquake as shear dislocation

Difficulties for “Internal” Sources

•  Wave equation not satisfied everywhere –  Discontinuity of displacement

–  Boundary conditions unknown

•  Kinematic description –  Distributed slip along fault, u(x, t)

1920s~1960s

Can we find body forces that are equivalent to earthquake faulting, in terms of producing the same seismic responses everywhere?

YES!!!

Seismic Moment Tensor

Moment and Moment Rate Function

Response for a force couple

Displacement due to M0(t)

Radiation Pattern

Displacement due to M0(t)

Static deformation