Tutorial:
Understanding seismic radiation patterns
(with example matlab sources) 

Gunnar Jahnke

 Last change: 08. Nov. 2004

First release.
Screenshot (radiation pattern and seismograms) Motivation:

Radiation patterns of seismic sources are complex 3D structures. It is difficult to derive their properties solely from textbook formulas and 2D diagrams.

The Matlab routine anaseis.m shows the 3D radiation pattern and the corresponding seismograms for various source types.

By interactively rotating the radiation pattern in the 3D window (top right window) features such as nodal plane orientations and directions of maximum amplitudes can be understood.

The radiation patterns with plotted receiver locations in the 3D window together with the seismogram window (bottom right window) link the intuitive radiation patterns with the rather abstract seismogram representations of wave fields.

Download: anaseis.m

Any comments, especially bug reports, are welcome!


Usage:

Copy anaseis.m to your Matlab search path.
Enter anaseis at the matlab prompt.
After a second two windows pop up showing the radiation pattern and seismograms for the default source which is a double couple in the YZ plane.

For different sources type: anaseis(stype) where 'stype' is one of:
'DC_XY' 'DC_XZ' 'DC_YZ' (double couple sources)
'EXPL' (explosion source)
'SF_Z' (single force in Z-direction).

For 3D-rotating the radiation pattern press and hold your left mouse button in the top window and move the pointer. A wire frame box appears showing the actual orientation. After releasing the mouse button the radiation pattern is updated.

If this does not work, the Matlab feature "mouse based 3-D rotation" is disabled. To activate it select the menu entry "Tools->Rotate 3D" or enter "rotate3d on" at the Matlab prompt.

The seismogram window shows the corresponding traces for a Ricker source time function. Besides the x/y/z components the related traces in the ray coordinate system r/theta/phi are shown where r denotes the source-receiver direction, theta is the vertical and phi the horizontal angular direction.

Try also "anaseis help" for additional information.