Variable Star Symbols for Seismicity Plots

Duncan C. Agnew

Published 2014, SCEC Contribution #1931

At least since Mallet (1858) seismicity maps have been a way of showing earthquake activity, but, because earthquake size varies greatly, it is difficult to provide an accurate representation of the spatial variation of total seismic energy or moment release. The most common approach, using for each earthquake a single geometric figure of varying size, creates substantial overlap between large symbols. To reduce overlap and provide a more distinctive gradation, I propose a family of symbols in which size and shape vary together, from polygonal to star-shaped as their size increases. Two functions determine how symbol size and shape vary with value, and even a simple parametrization gives considerable flexibility in symbol design. Tests show that, given an appropriate key, the symbol value can be estimated to within better than 5% of the range covered.

Agnew, D. C. (2014). Variable Star Symbols for Seismicity Plots. Seismological Research Letters, 85(4), 775-780. doi: 10.1785/0220130214.