A Focal Mechanism Diagram Generator for Analysis of Earthquake First Motions

Declan G. De Paor, Elizabeth Wilson, and Heather Melanson

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.