This supplement contains two figures that provide slightly different views of what is shown in Figures 1d and 6 of the main article, and a software file that includes code and data files to demonstrate the equalization method, though not to make the plots.
The EVC Centennial catalog used here is the global seismicity catalog of Engdahl and Villaseñor (2002), which includes improved locations and a variety of magnitude estimates.
Figure S1. This figure corresponds to Figure 1d in the text, showing the earthquakes (magnitude ≥6.0, depth < 60 km) from the EVC catalog, plotted against time on an equalized magnitude scale: (a) the reduced level of seismicity between 1900 and 1912, magnitudes 6.5–6.7; (b) the reduced level between 1912 and 1922, magnitudes 6.5–6.9; (c) the reduced level from 1922–1952, magnitudes 6.7–6.9; (d) the increased level from 1922–1952, magnitude 6.6; (e) the greatly reduced level from 1922–1952, magnitude 6.5; and (f) the reduced level from 1964–1968, magnitudes 6.3 and 6.4. Colored areas highlight some of the inhomogeneities that appear.
Figure S2. This figure shows the same seismicity as Figure 6 in the main article, namely that for 1992 in southern California, on an equalized magnitude scale but a constant time scale.
Download: Eqldens [gzipped tape archive file; ∼53 KB]. This is a gzipped TAR file containing the source code for three FORTRAN programs: seismodith to provide Gutenberg–Richter dithering of magnitudes; eqldens to create equalized magnitudes; and julcon, a calendar conversion program used in the script doall.sh, which compiles the programs, gets a copy of the EVC catalog from the Web, and processes it to create a file giving equalized magnitudes against time (equalized_centennial) and a file giving the scaled values for specific magnitudes (equalized_scale). The file equalized_test is provided to show what results should be obtained for equalized_centennial.
Engdahl, E. R., and A. Villaseñor (2002). Global Seismicity: 1900–1999, in International Handbook of Earthquake and Engineering Seismology, Part A, W. H. K. Lee, H. Kanamori, P. C. Jennings, and C. Kisslinger (Editors), Elsevier Academic Press, New York, New York, 665–690.
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