On January 1, 2008, the Southern California Seismic Network began using an updated method of measuring local magnitude (Ml). To ensure consistency in the Southern California Earthquake Catalog, we will begin recalibrating the Ml magnitudes for events between January 1, 1992 to January 1 2008 using this same method.

The processing will be starting with events in December 2007, and going back one month at a time. These recalibrated magnitudes will be seen in the catalog search page. Processing begins May 1, 2009.

If you wish to view historical data with the legacy magnitudes, text files of the catalogs can be found here:
http://www.data.scec.org/ftp/catalogs/SCSN_pre2008/

Information on the revised Ml calculation is given the publication:
R. A. Uhrhammer, M. Hellweg, K. Hutton, P. Lombard, A. W. Walters, E. Hauksson and D. Oppenheimer; California Integrated Seismic Network (CISN) Local Magnitude Determination in California (to be submitted) to BSSA, 2009