De Paor, D., Wilson, E. and Melanson, H. 2006.   A Focal Mechanism Diagram Generator for Analysis of Earthquake First Motions. In: (Ed.) Daniel Köhn, and Declan De Paor, General Contributions 2006, Journal of the Virtual Explorer, Electronic Edition, ISSN 1441-8142, volume 21, paper 2, doi:10.3809/jvirtex.2006.00145

A Focal Mechanism Diagram Generator for Analysis of Earthquake First Motions

Declan G. De Paor

Department of Physics, Worcester Polytechnic Institute, Worcester MA 01609

<declan@wpi.edu>

Elizabeth Wilson

Department of Earth Sciences, Boston University, Boston MA 02215

Heather Melanson

Department of Earth Sciences, Boston University, Boston MA 02215

Abstract

We present an interactive method for analyzing earthquake first motions and generating focal mechanism diagrams using Flash Actionscript™. A shockwave flash movie file call FirstMo.swf monitors first arrival data stored in an external data file. Data may be in the form of XML-tagged arrival directions (plunge, trend, and up/down ground motion), or the data may be plotted on a stereographic projection and imported as a jpeg image. Variables under user control include nodal plane orientations, moment magnitude scale, transparency, and background map. Focal depths are color-coded using a standard UGSG look-up table.

Tsunamigenic earthquakes have characteristic moment tensor solutions, thus rapid rendering and enhanced visualization of focal mechanism diagrams may help with the dissemination of critical information to public safety personnel and the general public.

Keywords: XML, geophysics, earthquakes, focal mechanism, first motion, moment tensor solution, geophysical beach ball, visualization, Flash™, ActionScript™