3d visualisation of earthquake focal mechanisms

Introduction

On maps the focal solution of earthquakes is often represented as a stereographic projection of calculated nodal planes with the quadrant shaded where first arrival of seismic waves at the receiving seismometer is compressive. In effect this projection looks like a simple beach ball. In a 3d visualisation environment such as gOcad it becomes desirable to represent focal solution as actual 3d spheres with shaded quadrants. Here I make available a package which provides this functionality and other related tasks for the gOcad environment. It consists of some programs (awk scripts) which create the objects in a gOcad format and a graphical interface to these programs which is implemented as a so-called gOcad wizard. There is an updated version (see below).

Screenshots

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First screen of visualisation wizard. Specify file name and type for import. Example pictures on left shows some beach balls.

(click for full image, 32kb)
Choose type of visualization in wizard. Example picture on left shows nodal planes and P-/T-axes.

(click for full image, 79kb)
Import attribute field of fpfit file as properties. Example picture on left shows a point cloud.

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First screen of Filter and Export wizard. There are fields to specify object, filter values and a file name. Exported files can be reimported with the visualisation wizard.

How to use ?

Please consult the README file which accompanies the package for usage and installation instructions.

Download

I prepared two archives, one for Irix and one for Linux. Except for the scripts and the wizard which should run on any architecture, they contain precompiled binaries of the proj program which is used for conversion of geographic coordinates into UTM coordinates.

Download (free for academic use),

the Linux archive beachball_linux.tar.gz (508kb)
the Irix archive beachball_irix.tar.gz (581kb)

Update

I rewrote the wizard to make it self-contained. The main change that it works now on all platforms, irix, linux and nt. It is self-contained, no external scripts are needed, just load the wizard. The expected file format is the same except now depth is in m instead of km. Another highlight is that besides beachballs just single circular disks with a slip vector can be produced.

Summary of changes:

supports all gocad platforms
much simplified installation, load and use
optimized 100 triangles beach balls (reduced from 414 triangles)
new disk with slip vector representation
use existing vset with properties as input
scaling of balls works now
easy to add other representations
no utm projection support (use other tools, see proj)
no fpfit import (use excel or old awk script and gocad xyzimport)

It is now possible to use an existing vset with defined properties as input. It may often be advantageous to first load a file using the xyzproperty import filter, maybe subset it, and then convert it to beachballs. The names of the properties is fixed (strike or dipdirection, dip, rake, magnitude, name). You can also specify a data file directly.

The wizard writes and loads files. Therefore the directory from which gocad was started ("Start in" in windows shortcut) must be accessible to the user.

You are welcome to look at the wizard source. It is quite instructive and has many tricks which are not in the "Writing Wizards in Gocad" tutorial.

Download (free for academic use) the wizard here .

Comments

If you like this package and use it for your work, please contact the author .

Enjoy,

A. Plesch

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2/11/02